FromDev

5 Excellent Opensource Database Change Management tool for complex projects

noreply@blogger.com (Sachin) — Sat, 21 Jan 2012 16:55:00 +0000

Database change management tools are of great help to developers and database administrators. These tools increase the efficiency of their work. Earlier database administrators used command lines to delete, create and edit databases. However now with the introduction of Database Change Management tools, the work load of the DBA’s has reduced considerably.

Below are given 7 different types of open source database change management tools which are of great help to the DBA’s:

LIQUIBASE

Key Features

Efficiently manage multiple databases
Extensible to make changes
Able to keep a track record of database changes
Execution can take place through Maven, command line, Ant etc.

http://www.liquibase.org/download

DBDeploy

Key Features

Simple to use
Works well with Ant

http://code.google.com/p/dbdeploy/downloads/list

Ruckusing

Key Features

Portability: The migration files are initially written in PHP5 which are further translated to appropriate SQL during runtime. Thus providing an option of supporting any RDBMS with a single migration file.
The ability to move (up and down) to particular migration state

https://github.com/ruckus/ruckusing-migrations/downloads

DBSource Tools

Key Features

Can be used to compare schemas
Strong database scripter

http://dbsourcetools.codeplex.com/

Nextep Open Designer

Key Features

Ease of merging database during development
Helps in integrating deployment processes

http://www.nextep-softwares.com/index.php/products

Tasks like maintaining and updating the relational databases are done by these tools very quickly and efficiently. These tools also help in maintaining the complex projects thus making the task easier for developers. Thus if you wish to increase your efficiency then these Database Management Tools are highly recommended.

Hope you found this list useful! What are the tools you have used for database management? Please don't forget to share with us in comments.

8 Best Software Requirements Analysis Books Every Business Analyst Must read

noreply@blogger.com (Sachin) — Sun, 15 Jan 2012 04:55:00 +0000

Every aspiring business analyst in software development field must be aware of the software requirements analysis methods, tools and techniques to ensure timely and easy implementation of software projects. Below is given the list of eight best software requirement analysis books which should be read by every business analyst.

Software Requirements 2

Writing Effective Use Cases

The Software Requirements Memory Jogger: A Pocket Guide to Help Software And Business Teams Develop And Manage Requirements (Memory Jogger)

Agile Software Requirements: Lean Requirements Practices for Teams, Programs, and the Enterprise (Agile Software Development Series)

Software Requirements and Specifications: A Lexicon of Practice, Principles and Prejudices (ACM Press)

More About Software Requirements: Thorny Issues and Practical Advice

Seven Steps to Mastering Business Analysis

The Business Analyst's Handbook

The above given books ensure to provide the knowledge which will be helpful to both experienced and inexperienced project team members and business analysts.

Hope you found this list useful! What are the best books you have read? Please don't forget to share with us in comments.

25 Best Free Eclipse Plug-ins for Java Developer to be Productive

noreply@blogger.com (Sachin) — Sat, 07 Jan 2012 17:57:00 +0000

Eclipse offers an integrated development environment having an extensible plug-in system. This enables Eclipse to provide all functionality on the top of its runtime system. It’s also different from other applications (where the functionalities provided by plug-ins are mostly hard coded). Having the appropriate Eclipse plug is important, since it facilitates the Java developers to seamlessly develop and implement applications which are J2EE and service-based. Eclipse plug-ins also helps them to implement their application on several types of application infrastructures.

Below is the list of 25 best free Eclipse plug-ins for a developer to be more productive -

Code Quality Plugins

FindBugs

Checkstyle

ECLemma

JDepend4Eclipse

PMD

http://pmd.sourceforge.net/eclipse/

SourceHelper

Structure101

Text Editor Plugins

AnyEdit Tools

Eclim

Eclipse-rbe

Dependency Management

Apache IvyDE

M2eclipse (Maven Plugin)

Version Control Integration Plugins

Subclipse

EGit

MercurialEclipse

P4Eclipse

Framework Development

Spring Tool Suite

Spring IDE

Hibernator

JbossTools

Other Utility Plugins

ASM - Bytecode Outline plugin

http://download.forge.objectweb.org/eclipse-update/

Mylyn - Task Management

Eclipse Launcher

FileSync

Log4E

All in all, plug-ins allows Eclipse to be coded in other languages. Eclipse plug-ins is indispensable nowadays, since it greatly streamlines Java applications and reduces the complexity of Java. However, installing too many plug-ins can slow down Eclipse. Hence you require selecting the plug-ins judiciously.

There are a number of other productivity plug-ins too, besides the ones mentioned. Checkstyle, JBoss Tools and Jadclipse are three of them. Do let us know if you have used some other plug-ins which you were impressed with.

9 Excellent Books Product Managers must read to Create Great Products

noreply@blogger.com (Sachin) — Sun, 25 Dec 2011 08:19:00 +0000

A product manager’s role involves designing, operating, building and maintaining a good service. The role of product manager differs from one project to another which involves working on directing market strategies and products, and also educating executives about the related strategies. The below list of books covers almost all the topics related to product management, presentations and Agile, and are highly recommended to entry and mid- level product managers -

42 Rules of Product Management: Learn the Rules of Product Management from Leading Experts "from" Around the World

Inspired: How To Create Products Customers Love

The Product Manager's Desk Reference

Take Charge Product Management: Take Charge of Your Product Management Development; Tips, Tactics, and Tools to Increase Your Effectiveness as a Product Manager

Agile Excellence for Product Managers: A Guide to Creating Winning Products with Agile Development Teams

Agile Product Management with Scrum: Creating Products that Customers Love (Addison-Wesley Signature Series (Cohn))

Product Strategy for High Technology Companies

The Product Managers Handbook

The Art of Product Management: Lessons from a Silicon Valley Innovator

A product manager has to manage a number of activities, departments and provide tools and information to meet the requirements of various departments in an organization. The above given list of books helps a product manager to assess the requirements, situations and handle the various circumstances efficiently.

Hope you found this list useful! What are the best books you have read? Please don't forget to share with us in comments.

10 Excellent OpenSource VPN Solutions for your Business

noreply@blogger.com (Sachin) — Sun, 18 Dec 2011 00:17:00 +0000

VPN connections are important for business establishments because of the sensitivity of the data that are being transmitted across the web. It is quite easy to use snooping software to crack the connection and trap the packets that are being transmitted through the web. Both wired and Wi-Fi connections don’t allow the basic security of the data. VPN systems thus allow a secure connection which encrypts the data and ensures that it cannot be tapped into.

OpenVPN

The Securepoint TERRA

Tunnelblick

Tomato VPN

iPIG

LogMeIn Hamachi

Shrew Soft’s VPN

LiliVPN

KOVpn

OAST

A Virtual Private Network (VPN) Solution denotes the hardware, software, encryption and authentication protocols used to ensure that users across two physical locations separated by a few miles or a few thousand or more, can securely exchange data and access all network data without any third party interfering or accessing the same. VPN uses an internet connection for transmitting the information packets to and fro. It uses encryption to ensure that the packets which are transmitted over the internet cannot be deciphered or read by third party software or humans. It also uses authentication protocols to ensure that only computers which are given access to the network, can access it.

Hope you found this list useful, What is the VPN solution you have use? Please don't forget to share with me in comments.

11 Most Influential Books Every Programmer / Developer Must Read

noreply@blogger.com (Sachin) — Thu, 01 Sep 2011 01:09:00 +0000

Every programmer needs to learn new and updated programming methods as per the changes in technology to tackle complex situations. You should make use of clean code and latest programming methods to design efficient, scalable and accurate programs. The 11 most influential books which provide enormous information for a computer programmer are –

Code Complete

Pragmatic Programmer

The book “The Pragmatic Programmer” explains the mechanics of programming which helps you to write flexible and adaptable code. It provides guidelines to use tools and test codes effectively. Moreover, it provides many concepts to develop high quality code, and uses the pragmatic approach towards programming.

Author Site: The Pragmatic Programmer

Structure and Interpretation of Computer Programs

Professors Abelson and Sussman offer researched material for students to learn complex programming languages in the book “Structure and Interpretation of Computer Programs”. This provides answers to many difficult questions of programming. Additionally, the book provides simple solutions to complex programming. The book further explains the four trends of programming languages – imperative, object-oriented, logic based and applicative programming.

C Programming Language (2nd Edition)

The book by Kernighan and Ritchie provide classic programming structures for hardcore C programmers, which includes- the use of data types, if/else, for, printf, while, functions, arrays, variables etc. It even touches upon good programming methods and code reuse.

Introduction to Algorithms

A series of mathematical operations and algorithm is provided by the book which is required for core programming. The lessons on introduction to algorithm provide programming courses designed specifically for college students learning programming courses. The book is written by Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest and Clifford Stein.

Refactoring: Improving the Design of Existing Code

The book written by Martin Fowler, Kent Beck, John Brant, William Opdyke and Don Roberts deals with refactoring, principles of refactoring, smell codes, building test scripts, composing methods, organizing data, designing methods, generalization and using tools. It is a good book on UML, COM related technology, and provides different approaches for software development. The book explains numerous refactoring methods to eliminate smell (code).

The Mythical Man-Month

The book by Frederick P. Brooks provides information into the various developments in software tools and environment for the last 21 years. It also details man-month system, second system effect, the conceptual integrity, pilot plant, documentation, communication, code freezing, system versioning and tools.

The Art of Computer Programming

The book is written by Donald Knuth and it provides chapters on fundamental algorithm, sorting & searching, semi-numerical algorithm, syntactic algorithms, combinatorial algorithm, compilers and the theory of context free languages. The book can be used as a reference by a programmer.

Clean Code: A Handbook of Agile Software Craftsmanship

The book “Clean Code: A Handbook of Agile Software Craftsmanship” by Robert C. Martin tells about clean code practices and suggests the Boy Scout Rule to write clean code. The code examples explained in the books are mostly in Java but the guidelines have also been explained in other languages. It is a great book for object orientated coding.

Coders at Work: Reflections on the Craft of Programming

The book “Coders at Work: Reflections on the Craft of Programming” written by Peter Seibel is based on conversation with computer scientists and great programmers. The whole concept is based on the series of 15 interviews which is written with an introduction in the format of transcripts. The Q & A part explains how programmers learn programming and practice it, and what their views of expert programmers regarding future programming are.

CODE: The Hidden Language of Computer Hardware and Software

The book “CODE: The Hidden Language of Computer Hardware and Software” by Charles Petzold deals with a number of programming concepts starting from number systems - decimal, octal, binary to high level languages. The book explains packet based communication protocols and TCP. Many chapters are about hardware concepts and five chapters are devoted for software and explain about the operating system, floating point arithmetic and GUIs.

It is very important for a programmer to write clean and reusable code that can easily handle complex programming and system requirements. Thus these eleven books provide you in-depth information which can be used to improve coding practices.

Hope you found this list useful, What are the most influential books you have read? Please don't forget to share with me in comments.

Top 10 RSS Feeds a Java Developer Must Subscribe to be on Cutting-Edge Technologies

noreply@blogger.com (Sachin) — Fri, 29 Jul 2011 19:07:00 +0000

RSS feed gives web readers the freedom to choose from bulk of information spread across the World Wide Web. Though there are ways to choose, its not easy to decide what RSS feed you must subscribe and/or NOT subscribe.

For choosing the correct feeds, it's important that you search the internet extensively. Below are the Top ten feeds we think perfectly fits the need of a Java Developer to be up to date on cutting edge technologies and related news.

MartinFowler.com

MortinFowler.com RSS Feed

Coding Horror

Codinghorror RSS Feed

DZone

DZone Front Page RSS Feed

Webappers

WebAppers RSS Feed

TechCrunch

TechCrunch RSS Feed

Digg.com

Digg Technology RSS Feed

Oracle Technology Network for Java Developers [formerly known as Sun Developer Network (SDN) ]

Sun Developer Network RSS Feed

IBM's DeveloperWorks

DeveloperWorks RSS Feed

O' Reilly OnJava

OnJava RSS Feed

Reddit Programming

OnJava RSS Feed

It's quintessential for a Java developer to subscribe to some of the best RSS feeds, in order to be in sync with latest developments in technology, and consequently utilize the knowledge of the latest software breakthroughs for better Java programming and development. At the moment, very few web avenues can match the hassle free and minute by minute updates of RSS feeds.

Really simple syndication or RSS refers to a syndication format which is used to view updated news, headlines, videos and audios in the standard format. An RSS feed contains a channel, a title, link, description and language followed by series of items. The original RSS was 0.90 version designed by Netscape. UserLand later evolved it to form 0.9 x branches, which can be used for metadata rich syndication. RSS feeds prevent the need to individually visit websites to see the latest content or modified content as you automatically get it through feeds anytime, as per your convenience.

Do you subscribe to a RSS feed which is not part of this list? Please don't forget to share it with me in comments section & I will try to include it in the list.

Top 10 Open Source Web Application Firewalls (WAF) for WebApp Security

noreply@blogger.com (Sachin) — Fri, 01 Jul 2011 18:02:00 +0000

Web application firewalls provide security at the application layer. Essentially, WAF provides all your web applications a secure solution which ensures the data and web applications are safe.

A web application firewall applies a set of rules to HTTP conversation to identify and restrict the attacks of cross site scripting, SQL injections etc. You can also get web application framework and web based commercial tools, for providing security to web applications. Web Application Firewalls allows you to customize the rules by identifying and blocking malicious content. Some of the most popular and widely used open source web application firewalls for web application security are –

ModSecurity (Trustwave SpiderLabs)

AQTRONIX WebKnight

ESAPI WAF

WebCastellum

Binarysec

Guardian@JUMPERZ.NET

OpenWAF

Ironbee

Profense

Smoothwall

Internet based protection is also provided by companies which provide security at the network layer with features such as packet filter. Besides, there are some other types of firewalls which are designed to ensure security of the database. Therefore, the criteria for selecting an open source WAF should be the types of vulnerabilities the WAF can prevent and the exact requirements that your company is having. This list of open source web application firewalls would hence assist you in determining the apt WAF for Webapp security.

Hope you found this list useful! What is your experience with WAF? Please don't forget to share with me in comments.

10 Excellent Free Open Source Projects to create your own CDN - Content Delivery Network

noreply@blogger.com (Sachin) — Fri, 24 Jun 2011 17:55:00 +0000

A content delivery network helps to host content such as images, media files, static content and style sheets of a large website by reproducing a copy of data through the various nodes of a network. Additionally, content delivery software helps to reduce load of websites and to improve downloading time of the websites. CDN is not just software; instead, it is a mix of hardware and software which helps to solve the problem of web content downloading and management using synchronization, logging, authentication and load balancing.

Here is the list of open source projects which can be used to create your own CDN –

Cacheboy

Mod CDN - Apache Module

CoralCDN

OpenCDN

Download OpenCDN

Phloem

Download Phloem

P2P-Next

MirrorBrain

CoDeeN

Mediaport.net

Firestarter Content Delivery System

CDN nodes are located in various geographical locations and these nodes work in cooperation with the requests of the client. Content delivery networks distribute the assets and use various techniques such as server load balancing, web caches, dynamic metafile generation, ‘anycasting’ and HTML rewriting to reduce client response time.

It’s essential that the CDN is located near the targeted customer, since that would result in faster page loads and resultantly, the customers browsing experience will be enhanced. If you are planning to set up a geo targeted website, an Opensource software listed in this article would enable you to quickly start a CDN. However, you may require hardware for running these. On the other hand, if you are building a website which has a worldwide presence, you should opt for niche CDN services such as Akamai.

There are a number of popular CDNs, besides the ones mentioned in this list. Please share with us in comments if you have used some other CDNs which you were impressed with.

15 Excellent and Cheaper Content Delivery Network (CDN) Alternatives to Akamai

noreply@blogger.com (Sachin) — Mon, 06 Jun 2011 22:51:00 +0000

A content delivery network system is a collection of internet servers which serves about one third of the most visited websites. The system improves speed of access for download-able data, applications, queries, web objects and media streams, as it increases the access bandwidth and reduces latency.

It contains copies of data located at different nodes of the selected servers, providing service from servers which are located geographically close to the user, hence saving access time. Furthermore, this unique method assists in reducing load on web application and improves scalability. There are several types of Content Deliver Networks which includes third party CDN providers too.

Akamai is one of the most famous CDNs which support many of the Fortune 50 sites. Akamai delivers between 15-30% of all Web traffic. Though Akamai is the leader, if your work is restricted to the US, there is no need to spend on Akamai as you can go for other efficient but cheap alternatives, such as the ones mentioned in this list.

Here is a list of 15 popular CDN alternatives to Akamai–

CoralCDN

Amazon CloudFront

CacheFly

MaxCDN

ProCDN

BitGravity

Limelight

CDNetworks

Swiftway

Edgecast

Cotendo

SoftLayer

GoGrid

CloudLayer

Level 3

There are a number of other popular CDNs, besides the ones mentioned in above list. Do let us know in comments section if you have used some other CDNs which you were impressed with.

10 Best Free Open Source Ecommerce Shopping Cart Applications For Business

noreply@blogger.com (Sachin) — Tue, 31 May 2011 18:09:00 +0000

To design and promote a new ecommerce website, you require deploying efficacious marketing, SEO tools and most importantly, an efficient shopping cart software. Shopping cart software should integrate an easy-to-use interface, safe transaction capability, good PCI security standards and a high speed service during the shopping transaction. Here is a list of the top 10 free open source e-commerce shopping cart applications:

Magento

OsCommerce

Apache OFBiz

KonaKart

PrestaShop

Jentla

Zen Cart

Batavi

DashCommerce

OpenCart

There are a number of other free open source ecommerce shopping cart applications for business; however the feature sets and ease of use are not at par with the aforementioned applications. All in all, the 10 ecommerce shopping cart applications discussed above are the most reliable, easy to use and feature rich open source free applications available for your business presently.

Hope you find this list useful, What is the best eCommerce shopping cart application you are using? Please don't forget to share with me in comments.

Guest Post by: Soumik Mukherjee

5 Best Core Java Books you must read as a developer

noreply@blogger.com (Sachin) — Fri, 22 Apr 2011 00:35:00 +0000

If you want success in JAVA, you do not need to enroll in a class. You could save a lot of money by simply reading a good book. When you refer to a good JAVA book, you are also more likely to get detailed and current information than you would from a teacher or from self-education since good JAVA books are written by authorities in the field, authorities with years of experience in JAVA coding and an educational background in the same. The fact that there are many options available is also a big plus. Below are some great options:

Thinking in Java

Java(TM) Puzzlers: Traps, Pitfalls, and Corner Cases

Effective Java (2nd Edition)

Java Concurrency in Practice

Head First Java, 2nd Edition

Hope you found this list useful! What are the best books you have read? Please don't forget to share with us in comments.

Guest Post by: Eunice Nungari

How To Change Company Logo Liferay Portal 6.x

noreply@blogger.com (Sachin) — Mon, 14 Feb 2011 19:27:00 +0000

Liferay bundle (Tomcat) comes with a default company logo for liferay.com. In this post I am going to cover 2 ways to change this logo with your own company logo/picture.

How to change company logo - Administrator Style

Login to Liferay Portal with a admin user id. (The default user id is : test@liferay.com and password is: test)
On the top toolbar go to Manage - Control Panel

On the left navigation bar go to Settings Link in "Portal" Section. Settings page should be displayed.

On Settings page go to "Display Settings" link in Miscellaneous section on right navigation menu.

Click on the "Change" link and select your company logo.
Click on the "Save" button at the right navigation menu.
Now click on the "Back to Liferay" link on top navigation bar.

How to change company logo - Developer Style

Overriding portal default configuration

image.default.company.logo=company_logo.png

Copy Files in server CLASSPATH

\tomcat-\webapps\ROOT\WEB-INF\classes Both of these files needs to be in server CLASSPATH to be read by the portal.

Restart server

Refresh the browser window and changes should be visible on the portal home page.

Watch this Youtube Video to see all steps

24 Interview Questions & Answers for Hadoop MapReduce developers

noreply@blogger.com (Sachin) — Tue, 14 Dec 2010 20:05:00 +0000

A good understanding of Hadoop Architecture is required to understand and leverage the power of Hadoop. Here are few important practical questions which can be asked in a Hadoop Developer interview. This list primarily includes questions related to Hadoop Architecture, MapReduce, Hadoop API and HDFS.

What is a JobTracker in Hadoop? How many instances of JobTracker run on a Hadoop Cluster?

Client applications submit jobs to the Job tracker.
The JobTracker talks to the NameNode to determine the location of the data
The JobTracker locates TaskTracker nodes with available slots at or near the data
The JobTracker submits the work to the chosen TaskTracker nodes.
The TaskTracker nodes are monitored. If they do not submit heartbeat signals often enough, they are deemed to have failed and the work is scheduled on a different TaskTracker.
A TaskTracker will notify the JobTracker when a task fails. The JobTracker decides what to do then: it may resubmit the job elsewhere, it may mark that specific record as something to avoid, and it may may even blacklist the TaskTracker as unreliable.
When the work is completed, the JobTracker updates its status.
Client applications can poll the JobTracker for information.

How JobTracker schedules a task?

What is a Task Tracker in Hadoop? How many instances of TaskTracker run on a Hadoop Cluster

What is a Task instance in Hadoop? Where does it run?

How many Daemon processes run on a Hadoop system?

Following 3 Daemons run on Master nodes

Following 2 Daemons run on each Slave nodes

What is configuration of a typical slave node on Hadoop cluster? How many JVMs run on a slave node?

Single instance of a Task Tracker is run on each Slave node. Task tracker is run as a separate JVM process.
Single instance of a DataNode daemon is run on each Slave node. DataNode daemon is run as a separate JVM process.
One or Multiple instances of Task Instance is run on each slave node. Each task instance is run as a separate JVM process. The number of Task instances can be controlled by configuration. Typically a high end machine is configured to run more task instances.

What is the difference between HDFS and NAS ?

Following are differences between HDFS and NAS

In HDFS Data Blocks are distributed across local drives of all machines in a cluster. Whereas in NAS data is stored on dedicated hardware.
HDFS is designed to work with MapReduce System, since computation are moved to data. NAS is not suitable for MapReduce since data is stored seperately from the computations.
HDFS runs on a cluster of machines and provides redundancy usinga replication protocal. Whereas NAS is provided by a single machine therefore does not provide data redundancy.

How NameNode Handles data node failures?

Does MapReduce programming model provide a way for reducers to communicate with each other? In a MapReduce job can a reducer communicate with another reducer?

Can I set the number of reducers to zero?

Where is the Mapper Output (intermediate kay-value data) stored ?

What are combiners? When should I use a combiner in my MapReduce Job?

not guaranteed

What is Writable & WritableComparable interface?

org.apache.hadoop.io.Writable is a Java interface. Any key or value type in the Hadoop Map-Reduce framework implements this interface. Implementations typically implement a static read(DataInput) method which constructs a new instance, calls readFields(DataInput) and returns the instance.
org.apache.hadoop.io.WritableComparable is a Java interface. Any type which is to be used as a key in the Hadoop Map-Reduce framework should implement this interface. WritableComparable objects can be compared to each other using Comparators.

What is the Hadoop MapReduce API contract for a key and value Class?

The Key must implement the org.apache.hadoop.io.WritableComparable interface.
The value must implement the org.apache.hadoop.io.Writable interface.

What is a IdentityMapper and IdentityReducer in MapReduce ?

org.apache.hadoop.mapred.lib.IdentityMapper Implements the identity function, mapping inputs directly to outputs. If MapReduce programmer do not set the Mapper Class using JobConf.setMapperClass then IdentityMapper.class is used as a default value.
org.apache.hadoop.mapred.lib.IdentityReducer Performs no reduction, writing all input values directly to the output. If MapReduce programmer do not set the Reducer Class using JobConf.setReducerClass then IdentityReducer.class is used as a default value.

What is the meaning of speculative execution in Hadoop? Why is it important?

When is the reducers are started in a MapReduce job?

If reducers do not start before all mappers finish then why does the progress on MapReduce job shows something like Map(50%) Reduce(10%)? Why reducers progress percentage is displayed when mapper is not finished yet?

What is HDFS ? How it is different from traditional file systems?

HDFS is highly fault-tolerant and is designed to be deployed on low-cost hardware.
HDFS provides high throughput access to application data and is suitable for applications that have large data sets.
HDFS is designed to support very large files. Applications that are compatible with HDFS are those that deal with large data sets. These applications write their data only once but they read it one or more times and require these reads to be satisfied at streaming speeds. HDFS supports write-once-read-many semantics on files.

What is HDFS Block size? How is it different from traditional file system block size?

What is a NameNode? How many instances of NameNode run on a Hadoop Cluster?

What is a DataNode? How many instances of DataNode run on a Hadoop Cluster?

How the Client communicates with HDFS?

How the HDFS Blocks are replicated?

Can you think of a questions which is not part of this post? Please don't forget to share it with me in comments section & I will try to include it in the list.

7 Best Web Design & Development Books you must read

noreply@blogger.com (Sachin) — Fri, 12 Nov 2010 18:58:00 +0000

Are you a web developer and designer? Take a look at the following books which I found really valuable in developing & designing web based applications/sites. I would recommend these books as a must read for people who need to do mix of both Web Design and Development.

Don't Make Me Think: A Common Sense Approach to Web Usability, 2nd Edition

Letting Go of the Words: Writing Web Content that Works (Interactive Technologies)

Letting Go of the Words: Chapter 1

Even Faster Web Sites: Performance Best Practices for Web Developers

blog post

High Performance Web Sites: Essential Knowledge for Front-End Engineers

Eric Meyer on CSS: Mastering the Language of Web Design

JavaScript: The Definitive Guide

JavaScript: The Definitive Guide - PDF Download

jQuery in Action, Second Edition

jQuery In Action: Chapter 1

Hope you found this list useful! What are the best books you have read? Please don't forget to share with me in comments.

How to Debug connection leaks in c3p0 - A PooledConnection that has already signalled a Connection error is still in use

noreply@blogger.com (Sachin) — Fri, 05 Nov 2010 19:09:00 +0000

We saw below exception stack-trace which was randomly appearing on our Glassfish application server logs. The application was randomly being sluggish and not responding to requests.

Stacktrace

[#|2010-11-05T02:21:06.076-0700|WARNING|sun-appserver9.1|javax.enterprise.system.stream.err|_ThreadID=21;_ThreadName=DefaultQuartzScheduler_Worker-5;_RequestID=00530e25-f5e7-4a12-8ee6-7c0d00d649ed;|
org.hibernate.exception.GenericJDBCException: could not insert: [com.fromdev.AlertRecordImpl]
 at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:140)
 at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:128)
 at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
 at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2436)
 at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2856)
 at org.hibernate.action.EntityInsertAction.execute(EntityInsertAction.java:79)
 at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:273)
 at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:265)
 at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:184)
 at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
 at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
 at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1216)
 at com.fromdev.AlertJob.execute(ProductAlertJob.java:83)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:597)
 at org.springframework.util.MethodInvoker.invoke(MethodInvoker.java:276)
 at org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean$MethodInvokingJob.executeInternal(MethodInvokingJobDetailFactoryBean.java:260)
 at org.springframework.scheduling.quartz.QuartzJobBean.execute(QuartzJobBean.java:86)
 at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
 at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
Caused by: java.sql.SQLException: Closed Connection
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112)
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:146)
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:208)
 at oracle.jdbc.driver.PhysicalConnection.prepareStatement(PhysicalConnection.java:868)
 at oracle.jdbc.driver.PhysicalConnection.prepareStatement(PhysicalConnection.java:787)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:597)
 at com.mchange.v2.c3p0.stmt.GooGooStatementCache$1StmtAcquireTask.run(GooGooStatementCache.java:542)
 at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
|#]

[#|2010-11-05T02:21:06.076-0700|INFO|sun-appserver9.1|javax.enterprise.system.stream.out|_ThreadID=21;_ThreadName=DefaultQuartzScheduler_Worker-5;|02:21:06,076 WARN  NewPooledConnection           :486 [c3p0] A PooledConnection that has already signalled a Connection error is still in use!
|#]

[#|2010-11-05T02:21:06.091-0700|INFO|sun-appserver9.1|javax.enterprise.system.stream.out|_ThreadID=21;_ThreadName=DefaultQuartzScheduler_Worker-5;|02:21:06,076 WARN  NewPooledConnection           :487 [c3p0] Another error has occurred [ java.sql.SQLException: Closed Connection ] which will not be reported to listeners!
java.sql.SQLException: Closed Connection
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112)
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:146)
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:208)
 at oracle.jdbc.driver.PhysicalConnection.setAutoCommit(PhysicalConnection.java:1057)
 at com.mchange.v2.c3p0.impl.NewProxyConnection.setAutoCommit(NewProxyConnection.java:881)
 at org.hibernate.transaction.JDBCTransaction.toggleAutoCommit(JDBCTransaction.java:224)
 at org.hibernate.transaction.JDBCTransaction.rollbackAndResetAutoCommit(JDBCTransaction.java:216)
 at org.hibernate.transaction.JDBCTransaction.rollback(JDBCTransaction.java:192)
 at org.springframework.orm.hibernate3.HibernateTransactionManager.doRollback(HibernateTransactionManager.java:625)
 at org.springframework.transaction.support.AbstractPlatformTransactionManager.processRollback(AbstractPlatformTransactionManager.java:800)
 at org.springframework.transaction.support.AbstractPlatformTransactionManager.rollback(AbstractPlatformTransactionManager.java:777)
 at com.fromdev.UnitOfWork.rollback(UnitOfWork.java:45)
 at com.fromdev.AlertJob.execute(ProductAlertJob.java:84)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:597)
 at org.springframework.util.MethodInvoker.invoke(MethodInvoker.java:276)
 at org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean$MethodInvokingJob.executeInternal(MethodInvokingJobDetailFactoryBean.java:260)
 at org.springframework.scheduling.quartz.QuartzJobBean.execute(QuartzJobBean.java:86)
 at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
 at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
|#]

[#|2010-11-05T02:21:06.122-0700|INFO|sun-appserver9.1|javax.enterprise.system.stream.out|_ThreadID=21;_ThreadName=DefaultQuartzScheduler_Worker-5;|02:21:06,122 ERROR JobRunShell                   :212 Job DEFAULT.methodInvokingJobDetail threw an unhandled Exception: 
org.springframework.scheduling.quartz.JobMethodInvocationFailedException: Invocation of method 'execute' on target class [class com.fromdev.AlertJob] failed; nested exception is org.springframework.transaction.TransactionSystemException: Could not roll back Hibernate transaction; nested exception is org.hibernate.TransactionException: JDBC rollback failed
 at org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean$MethodInvokingJob.executeInternal(MethodInvokingJobDetailFactoryBean.java:269)
 at org.springframework.scheduling.quartz.QuartzJobBean.execute(QuartzJobBean.java:86)
 at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
 at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
Caused by: org.springframework.transaction.TransactionSystemException: Could not roll back Hibernate transaction; nested exception is org.hibernate.TransactionException: JDBC rollback failed
 at org.springframework.orm.hibernate3.HibernateTransactionManager.doRollback(HibernateTransactionManager.java:628)
 at org.springframework.transaction.support.AbstractPlatformTransactionManager.processRollback(AbstractPlatformTransactionManager.java:800)
 at org.springframework.transaction.support.AbstractPlatformTransactionManager.rollback(AbstractPlatformTransactionManager.java:777)
 at com.fromdev.UnitOfWork.rollback(UnitOfWork.java:45)
 at com.fromdev.AlertJob.execute(ProductAlertJob.java:84)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:597)
 at org.springframework.util.MethodInvoker.invoke(MethodInvoker.java:276)
 at org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean$MethodInvokingJob.executeInternal(MethodInvokingJobDetailFactoryBean.java:260)
 ... 3 more
Caused by: org.hibernate.TransactionException: JDBC rollback failed
 at org.hibernate.transaction.JDBCTransaction.rollback(JDBCTransaction.java:200)
 at org.springframework.orm.hibernate3.HibernateTransactionManager.doRollback(HibernateTransactionManager.java:625)
 ... 13 more
Caused by: java.sql.SQLException: Closed Connection
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112)
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:146)
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:208)
 at oracle.jdbc.driver.PhysicalConnection.rollback(PhysicalConnection.java:1161)
 at com.mchange.v2.c3p0.impl.NewProxyConnection.rollback(NewProxyConnection.java:855)
 at org.hibernate.transaction.JDBCTransaction.rollbackAndResetAutoCommit(JDBCTransaction.java:213)
 at org.hibernate.transaction.JDBCTransaction.rollback(JDBCTransaction.java:192)
 ... 14 more
|#]

[#|2010-11-05T02:21:06.122-0700|INFO|sun-appserver9.1|javax.enterprise.system.stream.out|_ThreadID=21;_ThreadName=DefaultQuartzScheduler_Worker-5;|02:21:06,122 ERROR ErrorLogger                   :2015 Job (DEFAULT.methodInvokingJobDetail threw an exception.
org.quartz.SchedulerException: Job threw an unhandled exception. [See nested exception: org.springframework.scheduling.quartz.JobMethodInvocationFailedException: Invocation of method 'execute' on target class [class com.fromdev.AlertJob] failed; nested exception is org.springframework.transaction.TransactionSystemException: Could not roll back Hibernate transaction; nested exception is org.hibernate.TransactionException: JDBC rollback failed]
 at org.quartz.core.JobRunShell.run(JobRunShell.java:214)
 at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
* Nested Exception (Underlying Cause) ---------------
org.springframework.scheduling.quartz.JobMethodInvocationFailedException: Invocation of method 'execute' on target class [class com.fromdev.AlertJob] failed; nested exception is org.springframework.transaction.TransactionSystemException: Could not roll back Hibernate transaction; nested exception is org.hibernate.TransactionException: JDBC rollback failed
 at org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean$MethodInvokingJob.executeInternal(MethodInvokingJobDetailFactoryBean.java:269)
 at org.springframework.scheduling.quartz.QuartzJobBean.execute(QuartzJobBean.java:86)
 at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
 at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
Caused by: org.springframework.transaction.TransactionSystemException: Could not roll back Hibernate transaction; nested exception is org.hibernate.TransactionException: JDBC rollback failed
 at org.springframework.orm.hibernate3.HibernateTransactionManager.doRollback(HibernateTransactionManager.java:628)
 at org.springframework.transaction.support.AbstractPlatformTransactionManager.processRollback(AbstractPlatformTransactionManager.java:800)
 at org.springframework.transaction.support.AbstractPlatformTransactionManager.rollback(AbstractPlatformTransactionManager.java:777)
 at com.fromdev.UnitOfWork.rollback(UnitOfWork.java:45)
 at com.fromdev.AlertJob.execute(ProductAlertJob.java:84)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:597)
 at org.springframework.util.MethodInvoker.invoke(MethodInvoker.java:276)
 at org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean$MethodInvokingJob.executeInternal(MethodInvokingJobDetailFactoryBean.java:260)
 ... 3 more
Caused by: org.hibernate.TransactionException: JDBC rollback failed
 at org.hibernate.transaction.JDBCTransaction.rollback(JDBCTransaction.java:200)
 at org.springframework.orm.hibernate3.HibernateTransactionManager.doRollback(HibernateTransactionManager.java:625)
 ... 13 more
Caused by: java.sql.SQLException: Closed Connection
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112)
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:146)
 at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:208)
 at oracle.jdbc.driver.PhysicalConnection.rollback(PhysicalConnection.java:1161)
 at com.mchange.v2.c3p0.impl.NewProxyConnection.rollback(NewProxyConnection.java:855)
 at org.hibernate.transaction.JDBCTransaction.rollbackAndResetAutoCommit(JDBCTransaction.java:213)
 at org.hibernate.transaction.JDBCTransaction.rollback(JDBCTransaction.java:192)
 ... 14 more
|#]

About our application

Our Web Application is regular JEE app using Glassfish v2/Spring/Hibernate with c3p0 connection pooling. We have used quartz scheduler for running our background jobs. One of our background job runs every night and does some intensive data processing which involves getting bulk data from database and processing it and then updating the database for each of the affected records.

How we used c3p0 Connection pooling

We have used c3p0 for connecting to our Oracle database connection pooling. As a added caution to not leak any connections we used one c3p0 config parameter, which allows us to clean unreturned connection for long time. The c3p0 pool has a configuration parameter unreturnedConnectionTimeout.

unreturnedConnectionTimeout defines a limit (in seconds) to how long a Connection may remain checked out. If set to a nozero value, unreturned, checked-out Connections that exceed this limit will be summarily destroyed, and then replaced in the pool. Obviously, you must take care to set this parameter to a value large enough that all intended operations on checked out Connections have time to complete. You can use this parameter to merely workaround unreliable client apps that fail to close() Connections. The Default value for this parameter is 0 Seconds. If set, if an application checks out but then fails to check-in [i.e. close()] a Connection within the specified period of time, the pool will unceremoniously destroy() the Connection. This permits applications with occasional Connection leaks to survive, rather than eventually exhausting the Connection pool. And that's a shame. Zero means no timeout, applications are expected to close() their own Connections. Obviously, if a non-zero value is set, it should be to a value longer than any Connection should reasonably be checked-out. Otherwise, the pool will occasionally kill Connections in active use, which is bad. This is basically a bad idea, but it's a commonly requested feature. Fix your applications so they don't leak Connections!

In our application the "unreturnedConnectionTimeout" value was set to 300 seconds (5 minutes), which is enough time for any web request to be processed. Infact most of our background jobs also completed within this limit. The problem started coming in when we had some enhancements added to the background job and it started taking more then 5 minutes. It was really difficult to debug this issue. Server was randomly not responding or being sluggish and getting OutOfMemory errors. Whenver we restarted the server and problem disappeared but hit us back after few days.

How to Debug this issue

To debug this we used a parameter in c3p0 config called "debugUnreturnedConnectionStackTraces"

If you set debugUnreturnedConnectionStackTraces to true, then a stack trace will be captured each time a Connection is checked-out. Whenever an unreturned Connection times out, that stack trace will be printed, revealing where a Connection was checked out that was not checked in promptly. debugUnreturnedConnectionStackTraces is intended to be used only for debugging, as capturing a stack trace can slow down Connection check-out.

After setting this parameter, we found below exception stacktrace in our logs and realized what could be the problem.

New Stacktrace

[#|2010-11-05T02:21:04.623-0700|INFO|sun-appserver9.1|javax.enterprise.system.stream.out|_ThreadID=20;_ThreadName=Timer-9;|
02:21:04,623 INFO  BasicResourcePool             :1392 A checked-out resource is overdue, and will be destroyed: com.mchange.v2.c3p0.impl.NewPooledConnection@1ee23c7
|#]

[#|2010-11-05T02:21:04.623-0700|INFO|sun-appserver9.1|javax.enterprise.system.stream.out|_ThreadID=20;_ThreadName=Timer-9;|02:21:04,623 INFO  BasicResourcePool             :1395 Logging the stack trace by which the overdue resource was checked-out.
java.lang.Exception: DEBUG ONLY: Overdue resource check-out stack trace.
 at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:506)
 at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525)
 at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
 at org.springframework.orm.hibernate3.LocalDataSourceConnectionProvider.getConnection(LocalDataSourceConnectionProvider.java:82)
 at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)
 at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
 at org.hibernate.jdbc.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:161)
 at org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1700)
 at org.hibernate.loader.Loader.doQuery(Loader.java:801)
 at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
 at org.hibernate.loader.Loader.doList(Loader.java:2533)
 at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)
 at org.hibernate.loader.Loader.list(Loader.java:2271)
 at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:452)
 at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:363)
 at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)
 at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1268)
 at org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
 at com.fromdev.alerts.AlertJob.execute(AlertJob.java:51)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:597)
 at org.springframework.util.MethodInvoker.invoke(MethodInvoker.java:276)
 at org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean$MethodInvokingJob.executeInternal(MethodInvokingJobDetailFactoryBean.java:260)
 at org.springframework.scheduling.quartz.QuartzJobBean.execute(QuartzJobBean.java:86)
 at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
 at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
|#]

The root causes

There were multiple issues in our application:

1. First root cause was poor performance of code. There was a code which was causing the background job to run slower. Due to this the job started taking more 300 seconds, which was greater than unreturnedConnectionTimeout value we had configured.

2. Second reason was not using finally block for releasing resources The root cause for Server being sluggish and going OutOfMemory (at times) was connection leaks. The leak was happening due to the session.close() not being called in a finally block.
I have seen this as most common cause of resource leaks in many java application. Releasing a resource at the end of the method does not gaurantee that it will always be called. Many developers make that mistake (like one of our teammates).

The resolution

We took following steps to resolve this issue
1. We Moved the session.close() call to finally block.
2. As a short term fix, we had to increase the value of unreturnedConnectionTimeout. We had set it to 600 seconds (10 mins).
3. The long term fix, was to identify the code which is taking longer time and split our jobs into shorter tasks. We used VisualVM CPU profiling to identify the bad performing methods and improved them. This also required us to make changes to the background processing logic.

References

Configuring Connection Testing
Hibernate: How To configure C3P0

Hope this helps you in debugging similar issues.

How to install Liferay 6.x on Glassfish v2 Clustered Environment

noreply@blogger.com (Sachin) — Wed, 15 Sep 2010 21:19:00 +0000

We recently started experimenting with Liferay 6.0.5 in Linux machine based Glassfish v2 clustered environment. The Bundled version of Liferay comes with Glassfish V3.0.1 which does not support clustering. So we wanted to experiment and see if this works with the v2 which supports clustering. At high level if you are interested in knowing that Liferay 6.0.5 on Glassfish v2 clustered environment works or not then the answer is YES, it does with flying colors :). You can continue reading if you are interested what are the steps we followed to do this.

This installation of Liferay was fairly simple on our 2 node clustered setup. This post assumes that you already have a Glassfish V2 cluster setup ready and want to run the Liferay war on it. Here are simple steps to do this

Download Liferay Glassfish Bundle

Liferay.com

Extract Liferay war and dependencies from bundle

liferay\liferay-portal-6.0.5\glassfish-3.0.1\domains\domain1\lib

portal-service.jar
portlet.jar
hsql.jar

Deploy Liferay war to Glassfish v2

liferay\liferay-portal-6.0.5\glassfish-3.0.1\domains\domain1\autodeploy

asadmin deploy --target [cluster_name] [war_location]\liferay-portal.war

Restart the cluster
Problems you may face

Out Of Memory Error

Go to Configurations> cluster1-config > JVM Settings > JVM Options (Tab)

Change the value of -Xmx option to maximum available on your system e.g. -Xmx1024m

Save the settings

Restart the cluster.

HSQL DB setup needs write permission on file system

12:29:29,588 INFO  [[/liferay-portal]:646] Initializing Spring root WebApplicationContext
Loading jar:file:/usr/local/tomcat/webapps/liferay-portal/WEB-INF/lib/portal-impl.jar!/portal.properties
12:29:54,699 WARN  [ThreadPoolAsynchronousRunner:608] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@1a0283e -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
12:29:54,708 WARN  [ThreadPoolAsynchronousRunner:624] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@1a0283e -- APPARENT DEADLOCK!!! Complete Status:
        Managed Threads: 3
        Active Threads: 3
        Active Tasks:
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@eeabe8 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2)
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@15837e8 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0)
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@be6108 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1)
        Pending Tasks:
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@d47880
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@1335b86
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@bdec44
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@e29f36
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@429be9
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@10a0d51
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@f04dae
Pool thread stack traces:
        Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2,5,main]
                java.lang.Thread.sleep(Native Method)
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1805)
                com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
        Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1,5,main]
                java.lang.Thread.sleep(Native Method)
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1805)
                com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
        Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0,5,main]
                java.lang.Thread.sleep(Native Method)
                com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1805)
                com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)


12:30:04,272 WARN  [BasicResourcePool:1841] com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@be6108 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception:
java.sql.SQLException: The database is already in use by another process: lockFile: org.hsqldb.persist.LockFile@d7a94b3d[file =/usr/local/data/hsql/lportal.lck, exists=false, locked=false, valid=false, ] method: openRAF reason: java.io.FileNotFoundException: /usr/local/data/hsql/lportal.lck (No such file or directory)
        at org.hsqldb.jdbc.Util.sqlException(Unknown Source)
        at org.hsqldb.jdbc.jdbcConnection.(Unknown Source)
        at org.hsqldb.jdbcDriver.getConnection(Unknown Source)
        at org.hsqldb.jdbcDriver.connect(Unknown Source)
        at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134)
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
        at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:148)
        at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
        at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
        at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
        at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
12:30:04,290 WARN  [BasicResourcePool:1841] com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@eeabe8 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (30). Last acquisition attempt exception:

Hope you found this post useful! What are the issues you faced during this install? Please don't forget to share with me in comments I may try to provide some help/guidance if possible.

12 JDBC Interview Questions & Answers for Java Developers - Java Database Connectivity

noreply@blogger.com (Sachin) — Thu, 19 Aug 2010 18:57:00 +0000

Java Database Connectivity API contains commonly asked Java interview questions. A good understanding of JDBC API is required to understand and leverage many powerful features of Java technology. Here are few important practical questions and answers which can be asked in a Core Java JDBC interview.

What are available drivers in JDBC?

JDBC technology drivers fit into one of four categories:

A JDBC-ODBC bridge provides JDBC API access via one or more ODBC drivers. Note that some ODBC native code and in many cases native database client code must be loaded on each client machine that uses this type of driver. Hence, this kind of driver is generally most appropriate when automatic installation and downloading of a Java technology application is not important. For information on the JDBC-ODBC bridge driver provided by Sun, see JDBC-ODBC Bridge Driver.
A native-API partly Java technology-enabled driver converts JDBC calls into calls on the client API for Oracle, Sybase, Informix, DB2, or other DBMS. Note that, like the bridge driver, this style of driver requires that some binary code be loaded on each client machine.

A net-protocol fully Java technology-enabled driver translates JDBC API calls into a DBMS-independent net protocol which is then translated to a DBMS protocol by a server. This net server middleware is able to connect all of its Java technology-based clients to many different databases. The specific protocol used depends on the vendor. In general, this is the most flexible JDBC API alternative. It is likely that all vendors of this solution will provide products suitable for Intranet use. In order for these products to also support Internet access they must handle the additional requirements for security, access through firewalls, etc., that the Web imposes. Several vendors are adding JDBC technology-based drivers to their existing database middleware products.

A native-protocol fully Java technology-enabled driver converts JDBC technology calls into the network protocol used by DBMSs directly. This allows a direct call from the client machine to the DBMS server and is a practical solution for Intranet access. Since many of these protocols are proprietary the database vendors themselves will be the primary source for this style of driver. Several database vendors have these in progress.

What are the types of statements in JDBC?

Statement

This interface is used for executing a static SQL statement and returning the results it produces.
The object of Statement class can be created using Connection.createStatement() method.

PreparedStatement

A SQL statement is pre-compiled and stored in a PreparedStatement object.
This object can then be used to efficiently execute this statement multiple times.
The object of PreparedStatement class can be created using Connection.prepareStatement() method. This extends Statement interface.

CallableStatement

This interface is used to execute SQL stored procedures.
This extends PreparedStatement interface.
The object of CallableStatement class can be created using Connection.prepareCall() method.

What is a stored procedure? How to call stored procedure using JDBC API?

CallableStatement cs = con.prepareCall("{call MY_STORED_PROC_NAME}");
ResultSet rs = cs.executeQuery();

What is Connection pooling? What are the advantages of using a connection pool?

Connection Pooling is a technique used for sharing the server resources among requested clients. It was pioneered by database vendors to allow multiple clients to share a cached set of connection objects that provides access to a database.

Getting connection and disconnecting are costly operation, which affects the application performance, so we should avoid creating multiple connection during multiple database interactions. A pool contains set of Database connections which are already connected, and any client who wants to use it can take it from pool and when done with using it can be returned back to the pool.

Apart from performance this also saves you resources as there may be limited database connections available for your application.

How to do database connection using JDBC thin driver ?

import java.sql.*;
class JDBCTest {
  public static void main (String args []) throws Exception
  {
        //Load driver class
        Class.forName ("oracle.jdbc.driver.OracleDriver");
         //Create connection
        Connection conn = DriverManager.getConnection
             ("jdbc:oracle:thin:@hostname:1526:testdb", "scott", "tiger");
                             // @machineName:port:SID,   userid,  password
 
        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery("select 'Hi' from dual");
        while (rs.next())
              System.out.println (rs.getString(1));   // Print col 1 => Hi
         stmt.close();
  }
}

What does Class.forName() method do?

- Load the class MyClass.

- Execute any static block code of MyClass.

- Return an instance of MyClass.

Class.forName("org.mysql.Driver");

static {
    try {
        java.sql.DriverManager.registerDriver(new Driver());
    } catch (SQLException E) {
        throw new RuntimeException("Can't register driver!");
    }
}

Which one will you use Statement or PreparedStatement? Or Which one to use when (Statement/PreparedStatement)? Compare PreparedStatement vs Statement.

Statement

PreparedStatement

Since its pre-compiled, Executing the same query multiple times in loop, binding different parameter values each time is faster. (What does pre-compiled statement means? The prepared statement(pre-compiled) concept is not specific to Java, it is a database concept. Statement precompiling means: when you execute a SQL query, database server will prepare a execution plan before executing the actual query, this execution plan will be cached at database server for further execution.)
In PreparedStatement the setDate()/setString() methods can be used to escape dates and strings properly, in a database-independent way.
SQL injection attacks on a system are virtually impossible when using PreparedStatements.

What does setAutoCommit(false) do?

    con.setAutoCommit(false);

    con.setAutoCommit(false);
    PreparedStatement updateStmt =
     con.prepareStatement( "UPDATE EMPLOYEE SET SALARY = ? WHERE EMP_NAME LIKE ?");
    updateStmt.setInt(1, 5000); updateSales.setString(2, "Jack");
    updateStmt.executeUpdate();
    updateStmt.setInt(1, 6000); updateSales.setString(2, "Tom");
    updateStmt.executeUpdate(); 
    con.commit();
    con.setAutoCommit(true);

What are database warnings and How can I handle database warnings in JDBC?

 //Retrieving warning from connection object
 SQLWarning warning = conn.getWarnings();
 
 //Retrieving next warning from warning object itself
 SQLWarning nextWarning = warning.getNextWarning();
 
 //Clear all warnings reported for this Connection object. 
 conn.clearWarnings();

 
 //Retrieving warning from statement object
 stmt.getWarnings();

 //Retrieving next warning from warning object itself
 SQLWarning nextWarning = warning.getNextWarning(); 
 
 //Clear all warnings reported for this Statement object. 
 stmt.clearWarnings();

 
 //Retrieving warning from resultset object
 rs.getWarnings();
 
 //Retrieving next warning from warning object itself
 SQLWarning nextWarning = warning.getNextWarning();
 
 //Clear all warnings reported for this resultset object. 
 rs.clearWarnings();

getWarnings()

SQLWarning.getNextWarning

clearWarnings()

getWarning()

What is Metadata and why should I use it?

 
 DatabaseMetaData md = conn.getMetaData();
 System.out.println("Database Name: " + md.getDatabaseProductName());
 System.out.println("Database Version: " + md.getDatabaseProductVersion());
 System.out.println("Driver Name: " + md.getDriverName());
 System.out.println("Driver Version: " + md.getDriverVersion());

 
     ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
     ResultSetMetaData rsmd = rs.getMetaData();
     int numberOfColumns = rsmd.getColumnCount();
     boolean b = rsmd.isSearchable(1);

What is RowSet? or What is the difference between RowSet and ResultSet? or Why do we need RowSet? or What are the advantages of using RowSet over ResultSet?

RowSet makes it possible to use the ResultSet object as a JavaBeans component. As a consequence, a result set can, for example, be a component in a Swing application.
RowSet be used to make a ResultSet object scrollable and updatable. All RowSet objects are by default scrollable and updatable. If the driver and database being used do not support scrolling and/or updating of result sets, an application can populate a RowSet object implementation (e.g. JdbcRowSet) with the data of a ResultSet object and then operate on the RowSet object as if it were the ResultSet object.

What is a connected RowSet? or What is the difference between connected RowSet and disconnected RowSet? or Connected vs Disconnected RowSet, which one should I use and when?

Connected RowSet

Example of Connected RowSet:

Disconnected RowSet

Example of Disconnected RowSet:

What is the benefit of having JdbcRowSet implementation? Why do we need a JdbcRowSet like wrapper around ResultSet?

This implementation makes it possible to use the ResultSet object as a JavaBeans component. A JdbcRowSet can be used as a JavaBeans component in a visual Bean development environment, can be created and configured at design time and executed at run time.

It can be used to make a ResultSet object scrollable and updatable. All RowSet objects are by default scrollable and updatable. If the driver and database being used do not support scrolling and/or updating of result sets, an application can populate a JdbcRowSet object with the data of a ResultSet object and then operate on the JdbcRowSet object as if it were the ResultSet object.

Can you think of a questions which is not part of this post? Please don't forget to share it with me in comments section & I will try to include it in the list.

5 Best Software Architecture Books you must read

noreply@blogger.com (Sachin) — Mon, 09 Aug 2010 23:17:00 +0000

Are you looking for the best software architecture books? Take a look at the following books which I found really valuable in understanding and effectively applying software architecture principles in real life. I would recommend these books as a must read for any software architect or developer regardless of language or background. (In addition to the 5 Best Design Pattern Books)

Software Systems Architecture: Working With Stakeholders Using Viewpoints and Perspectives

http://www.viewpoints-and-perspectives.info/

Agile Software Development, Principles, Patterns, and Practices

Working Effectively with Legacy Code

Beyond Software Architecture: Creating and Sustaining Winning Solutions

Enterprise Integration Patterns: Designing, Building, and Deploying Messaging Solutions

Hope you found this list useful! What are the best Software Architecture books you have read? Please don't forget to share with me in comments.

How to solve the Kaptcha error on Glassfish v31 in Linux

noreply@blogger.com (Sachin) — Wed, 23 Jun 2010 22:57:00 +0000

I was trying to run one of my existing web application on recently released Glassfish v31 in Linux environment. This is an early access release that will eventually replace GlassFish 3.0.1 with new clustering and centralized admin features.
In our web application we are using Kaptcha to avoid spamming on few pages, which is really simple to integrate with any java web application. ( A CAPTCHA helps you keep your site clean by automatically blocking spam. CAPTCHA is a contrived acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart.")

This application works perfectly fine with Tomcat 6, therefore ideally the application should run without any problem on any other JEE application server. We deployed the war file and everything started working except for the Kaptcha image. When we hit the Kaptcha URL (which of format http://host:port/app/kaptcha) directly it throws below error on the browser

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: PWC1243: Filter execution threw an exception

root cause

java.lang.NoClassDefFoundError: Could not initialize class sun.awt.X11GraphicsEnvironment

note The full stack traces of the exception and its root causes are available in the GlassFish3.1-b05 logs.
GlassFish3.1-b05

When we checked the server logs we found this exception stack-trace


[#|2010-06-22T16:55:30.908-0700|WARNING|glassfish3.1|javax.enterprise.system.container.web.com.sun.enterprise.web|_ThreadID=143;_ThreadName=Thread-1;|StandardWrapperValve[Kaptcha]: PWC1406: Servlet.service() for servlet Kaptcha threw exception
java.lang.NoClassDefFoundError: Could not initialize class sun.awt.X11GraphicsEnvironment
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:169)
        at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvironment.java:68)
        at java.awt.image.BufferedImage.createGraphics(BufferedImage.java:1135)
        at com.google.code.kaptcha.text.impl.DefaultWordRenderer.renderWord(DefaultWordRenderer.java:41)
        at com.google.code.kaptcha.impl.DefaultKaptcha.createImage(DefaultKaptcha.java:41)
        at com.google.code.kaptcha.servlet.KaptchaServlet.doGet(KaptchaServlet.java:82)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:844)
        at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1518)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:339)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:211)
        at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:211)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:171)
        at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:651)
        at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:591)
        at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:94)
        at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:87)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:158)
        at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:321)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:222)
        at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:165)
        at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:802)
        at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:705)
        at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:986)
        at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:178)
        at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:135)
        at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:102)
        at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:88)
        at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:76)
        at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:53)
        at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:57)
        at com.sun.grizzly.ContextTask.run(ContextTask.java:69)
        at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:526)
        at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:507)
        at java.lang.Thread.run(Thread.java:619)
|#]

[#|2010-06-22T16:54:38.458-0700|WARNING|glassfish3.1|javax.enterprise.system.container.web.com.sun.enterprise.web|_ThreadID=144;_ThreadName=http-thread-pool-8080(5);|StandardWrapperValve[Kaptcha]: PWC1406: Servlet.service() for servlet Kaptcha threw exception
java.lang.InternalError: Can't connect to X11 window server using 'localhost:10.0' as the value of the DISPLAY variable.
        at sun.awt.X11GraphicsEnvironment.initDisplay(Native Method)
        at sun.awt.X11GraphicsEnvironment.access$100(X11GraphicsEnvironment.java:52)
        at sun.awt.X11GraphicsEnvironment$1.run(X11GraphicsEnvironment.java:155)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.awt.X11GraphicsEnvironment.(X11GraphicsEnvironment.java:131)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:169)
        at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvironment.java:68)
        at java.awt.image.BufferedImage.createGraphics(BufferedImage.java:1135)
        at com.google.code.kaptcha.text.impl.DefaultWordRenderer.renderWord(DefaultWordRenderer.java:41)
        at com.google.code.kaptcha.impl.DefaultKaptcha.createImage(DefaultKaptcha.java:41)
        at com.google.code.kaptcha.servlet.KaptchaServlet.doGet(KaptchaServlet.java:82)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:844)
        at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1518)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:339)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:211)
        at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:211)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:171)
        at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:651)
        at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:591)
        at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:94)
        at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:87)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:158)
        at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:321)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:222)
        at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:165)
        at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:802)
        at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:705)
        at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:986)
        at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:178)
        at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:135)
        at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:102)
        at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:88)
        at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:76)
        at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:53)
        at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:57)
        at com.sun.grizzly.ContextTask.run(ContextTask.java:69)
        at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:526)
        at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:507)
        at java.lang.Thread.run(Thread.java:619)

The Root cause

If you look at the log message "Can't connect to X11 window server using 'localhost:10.0' as the value of the DISPLAY variable." This means the JRE abstract Windows toolkit is not able to initialize the graphics in this environment.

How to resolve this issue ?

To avoid this error we need to set headless JVM option to true in the server startup scripts.

-Djava.awt.headless=true

What is Headless mode?

This is extract from Sun Developer Network page

Headless mode is a system configuration in which the display device, keyboard, or mouse is lacking. Sounds unexpected, but actually you can perform different operations in this mode, even with graphic data.

Many methods in the java.awt.Toolkit and java.awt.GraphicsEnvironment classes, with the exception of fonts, imaging, and printing, require the availability of a display device, keyboard, and mouse. But some classes, such as Canvas or Panel, can be executed in headless mode. Headless mode support has been available since the J2SE 1.4 platform.

How to set Headless=true in Glassfish v31 Admin console?

This can be done from the Glassfish administration console.

Login to Glassfish Admin console
Go to - Configurations - Server Config - JVM Settings - JVM Options TAB - Select Add JVM Option
Add "-Djava.awt.headless=true" in the text field.
Hit "Save" button.
Restart the server.
Now the Captcha images should start working.

How to set Headless=true in Glassfish v31 command line?

This can be easily done using below asadmin commands

##Set the JVM option 
asadmin create-jvm-options -Djava.awt.headless=true
## Stop the server
asadmin stop-domain [mydomain]
## Start the server
asadmin start-domain [mydomain]

In general this error can seen on any server and the same solution should be applicable. I hope this post will save you some time on this issue, Let me know if you are facing any problem.

5 Best Design Pattern Books you must read as a Software Developer

noreply@blogger.com (Sachin) — Mon, 07 Jun 2010 18:07:00 +0000

Design patterns provide a structure in which problems can be solved. When solving a real problem, you have to consider many small variations of a solution to that problem to see whether any fits a design pattern.

To understand and get used to design patterns is really difficult. It can be done by studying applications of design patterns, not just the patterns. Reading several books with different perspective is really important.

Are you looking for the best design pattern books? Take a look at the following books which I found really valuable in understanding and effectively applying design patterns. I would recommend these books as must read for any software developer regardless of language or background.

Design Patterns: Elements of Reusable Object-Oriented Software

(By: Erich Gamma, Richard Helm, Ralph Johnson, John M. Vlissides)
As you probably already realized, this book is one of the seminal books on patterns in software development. If you are a professional software developer, you must read this. It isolates 23 of the most common patterns and presents them in detail. This book is popularly known as Gang of Four book (Due to gang of 4 great authors).

This book is not light reading though. The examples are based on heavy-duty design tasks an average programmer doesn't face, like language-parsing, toolkit creation, compiler writing, and the like. It makes one wonder how applicable many of the patterns are to less complex programming tasks.
The PDF version of this book can be downloaded from Gang Of Four eBook
Head First Design Patterns

(By: Elisabeth Freeman, Eric Freeman, Bert Bates, Kathy Sierra)
The Gang of Four book laid out the basics. The Head First book goes a lot further. It shows you good and bad way of applying the pattern. It gives strong reasoning behind the pattern.
While reading the Gang of Four book I found it very complicated to memorize the pattern. After reading this book it will be easy to memorize, reproduce and implement the patterns effectively.

Head First Design Patterns book is not just about design patterns. It's also a great introduction to object-oriented programming.
The PDF version of Chapter 3 can be downloaded from Head First Design Patterns eBook Chapter 3
Pattern Hatching: Design Patterns Applied

(By: John M. Vlissides)
Author John Vlissides is a member of the Gang of Four writers. He has an excellent writing style that is very engaging for this type of material. Besides going into some additional design patterns, and some pattern strengths and pitfalls, you get a fascinating behind the scenes look at what went on in the development stages of the original Design Patterns book.
Chapter 2 of this book is a must read where John develops a file system application. This book talks in great detail about which patterns suit best the needs of the application and which do not.
Refactoring to Patterns

(By : Joshua Kerievsky)

This is a good book for the software maintainer. In other words, it addresses 90% or 99% of the work that real programmers do. Just about every other software text on the market assumes that the project just started - the disks are empty and the compiler shrink-wrap is on the floor. I admit, that kind of programming is the most fun. It's just not realistic, though. Most work is rework, the kind demonstrated in this book. This also helps a lot in understanding anti-patterns.

This book does an excellent job of bringing patterns into coding, rather than relegating them just to design discussions. This includes twenty-seven pattern-directed refactorings with real-world code examples.
A PDF version of same book can be downloaded from Refactoring to Patterns eBook
Patterns of Enterprise Application Architecture

(By: Martin Fowler)

Martin Fowler clearly knows the field of Enterprise Application, he speaks with confidence of development experiences with projects that went live. This book covers the best practices of Enterprise Application Architecture. The first half of the book is a discussion of enterprise architecture in general. This book describes a set of patterns that work with a certain kind of application, business apps, but that are applicable to more than one platform.

This book is useful for both J2EE and .NET developers. This is particularly useful when attempting to gain an understanding of how application architectures differ between .NET and J2EE. I found the discussions on concurrency and transactions very valuable. Also if you have really complex business logic, you will find how the patterns presented in this book are useful.
The PDF version of this book can be downloaded from Patterns of Enterprise Application Architecture eBook

Hope you found this list useful, What are the best design patterns books you have read? Please don't forget to share with me in comments.

10 Simple String Utility Methods for Java Developer

noreply@blogger.com (Sachin) — Tue, 01 Jun 2010 19:49:00 +0000

String operations are common to all kind of programming. Java has many in built operations supported by String class. There are few functions which I observed commonly used and may be helpful to keep handy as StringUtil class with static methods.

Getting Exception Stack Trace to String value

public static String toString(Exception e) {

    StringWriter s = new StringWriter();
    e.printStackTrace(new PrintWriter(s));
    return s.toString(); 
}

Merging two String arrays

 
 /**
  * This String utility or util method can be used to merge 2 arrays of
  * string values. If the input arrays are like this array1 = {"a", "b" ,
  * "c"} array2 = {"c", "d", "e"} Then the output array will have {"a", "b" ,
  * "c", "d", "e"}
  * 
  * This takes care of eliminating duplicates and checks null values.
  * 
  * @param values
  * @return
  */
 public static String[] mergeStringArrays(String array1[], String array2[]) {
 
  if (array1 == null || array1.length == 0)
   return array2;
  if (array2 == null || array2.length == 0)
   return array1;
  List array1List = Arrays.asList(array1);
  List array2List = Arrays.asList(array2);
  List result = new ArrayList(array1List);  
  List tmp = new ArrayList(array1List);
  tmp.retainAll(array2List);
  result.removeAll(tmp);
  result.addAll(array2List);  
  return ((String[]) result.toArray(new String[result.size()]));
 }

Trim List of String

/**
 * This String utility or util method can be used to trim all the String
 * values in list of Strings. For input [" a1 ", "b1 ", " c1"] the output
 * will be {"a1", "b1", "c1"} Method takes care of null values. This method
 * is collections equivalent of the trim method for String array.
 *
 * @param values
 * @return
 */
public static List trim(final List values) {

 List newValues = new ArrayList();
 for (int i = 0, length = values.size(); i < length; i++) {
  String v = (String) values.get(i);
  if (v != null) {
   v = v.trim();
  }
  newValues.add(v);
 }
 return newValues;
}

Trim array of String

/**
 * This String utility or util method can be used to
 * trim all the String values in the string array.
 * For input {" a1 ", "b1 ", " c1"}
 * the output will be {"a1", "b1", "c1"}
 * Method takes care of null values.
 * @param values
 * @return
 */
public static String[] trim(final String[] values) {

 for (int i = 0, length = values.length; i < length; i++) {
  if (values[i] != null) {
   values[i] = values[i].trim();                                
  }
 }
 return values;

}

Unquoting the String

/**
 * This String util method removes single or double quotes
 * from a string if its quoted.
 * for input string = "mystr1" output will be = mystr1
 * for input string = 'mystr2' output will be = mystr2
 *
 * @param String value to be unquoted.
 * @return value unquoted, null if input is null.
 *
 */
public static String unquote(String s) {

 if (s != null
   && ((s.startsWith("\"") && s.endsWith("\""))
   || (s.startsWith("'") && s.endsWith("'")))) {

  s = s.substring(1, s.length() - 1);
 }
 return s;
}
/**
 * Same method as above but using the ?: syntax which is shorter. You can use whichever you prefer.
 * This String util method removes single or double quotes from a string if
 * its quoted. for input string = "mystr1" output will be = mystr1 for input
 *  
 * string = 'mystr2' output will be = mystr2
 *
 * @param String
 *            value to be unquoted.
 * @return value unquoted, null if input is null.
 *
 */
public static String unquote2(String s) {

 return (s != null && ((s.startsWith("\"") && s.endsWith("\"")) || (s
   .startsWith("'") && s.endsWith("'")))) ? s = s.substring(1, s
   .length() - 1) : s;

}

Extracting File Name from Absolute path

/**
* This method extracts the file name from absolute path of file
* As an example :
* 
*
* * For an input "c:\myDir\MyFile.java"
* The output will be : "MyFile"
* 
*
* 
*
* @param absoluteFileName File name with path
* @return FileName minus the path
*/

public static String extractFileName(String absoluteFileName) {

if (!isNullOrEmpty(absoluteFileName)) {

absoluteFileName = absoluteFileName.substring(absoluteFileName
.lastIndexOf(File.separatorChar) + 1, absoluteFileName.lastIndexOf("."));

}
return absoluteFileName;
}

Getting Array/List of tokens from String

/**
* This method is used to split the given string into different tokens at
* the occurrence of specified delimiter
* An example :
* "abcdzefghizlmnop" and using a delimiter "z"
* would give following output
* "abcd" "efghi" "lmnop"
*
* @param str The string that needs to be broken
* @param delimeter The delimiter used to break the string
* @return a string array
*/

public static String[] getTokensArray(String str, String delimeter) {

String[] data;
if(str == null){
    return null;
}

if (delimeter == null || "".equals(delimeter)
|| "".equals(str)) {
    data = new String[1];
    data[0] = str;
    return data;
} else {
    StringTokenizer st = new StringTokenizer(str, delimeter);
    int tokenCount = st.countTokens();
    data = new String[tokenCount];
    for (int i = 0; st.hasMoreTokens(); i++) {
    data[i] = st.nextToken();
}
return data;
}
}

/**
* This method is used to split the given string into different tokens at
* the occurrence of specified delimiter
* An example :
* "abcdzefghizlmnop" and using a delimiter "z"
* would give following output
* "abcd" "efghi" "lmnop"
*
* @param str The string that needs to be broken
* @param delimeter The delimiter used to break the string
* @return a string array
*/
 public static String[] getTokensArray(String str, String delimeter) {
  if (str != null) {
   return str.split(delimeter);
  }
  return null;
 }

/**
* This method is used to split the given string into different tokens at
* the occurrence of specified delimiter
* An example :
* "abcdzefghizlmnop" and using a delimiter "z"
* would give following output
* "abcd" "efghi" "lmnop"
*
* @param str The string that needs to be broken
* @param delimeter The delimiter used to break the string
* @return a instance of java.util.List with each token as one item in list
*/

 public static List getTokensList(String str, String delimeter) {
  if (str != null) {
   return Arrays.asList(str.split(delimeter));
  }
  return new ArrayList();
 }

Checking Starts/Ends with Ignoring the case

/**
* Check a String ends with another string ignoring the case.
*
* @param str
* @param suffix
* @return
*/
public static boolean endsWithIgnoreCase(String str, String suffix) {

    if (str == null || suffix == null) {
        return false;
    }
    if (str.endsWith(suffix)) {
        return true;
    }
    if (str.length() < suffix.length()) {
        return false;
    } else {
        return str.toLowerCase().endsWith(suffix.toLowerCase());
    }
}

/**
* Check a String starts with another string ignoring the case.
*
* @param str
* @param prefix
* @return
*/

public static boolean startsWithIgnoreCase(String str, String prefix) {

    if (str == null || prefix == null) {
        return false;
    }
    if (str.startsWith(prefix)) {
        return true;
    }
    if (str.length() < prefix.length()) {
        return false;
    } else {
        return str.toLowerCase().startsWith(prefix.toLowerCase());
    }
}

Converting String to set of Unique tokens

/**
* This method creates a set of unique string tokens which are separated by
* separator
*
* @param str
* @param separator
* @return
*/
public static Set getUniqueTokens(String str, String separator) {

 StringTokenizer tokenizer = new StringTokenizer(str, separator);
 Set tokens = new HashSet();
 while (tokenizer.hasMoreTokens()) {
     tokens.add(tokenizer.nextToken());
 }
 return tokens;
}

/**
* This method creates a set of unique string tokens which are separated by
* separator
*
* @param str
* @param separator
* @return
*/
public static Set getUniqueTokens(String str, String separator) {
 String [] tmpStr = str.split(separator);
 return new HashSet(Arrays.asList(tmpStr));
}

Masking Null String value

/**
* Return a not null string.
*
* @param s String
* @return empty string if it is null otherwise the string passed in as
* parameter.
*/

public static String nonNull(String s) {

if (s == null) {
    return "";
}
return s;
}

Can you think of a function which is not part of this list? Please don't forget to share it with me in comments section & I will try to include it in the list.

6 Simple ways to automatically update copyright year on a web page

noreply@blogger.com (Sachin) — Mon, 26 Apr 2010 19:11:00 +0000

Automatic update of copyright year would be a real smart thing to do for any website since its such a trivial thing many developer may not remember to update it manually every year.

Recently I observed this with twitter.com when they forgot to update the Copyright year from 2009 to 2010 for few months. Automatic update will avoid any such mistakes on your site. In this tutorial I am trying to capture most common ways where people may need to update copyright year in a website.

Using JSTL (JavaServer Pages Standard Tag Library)

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt"%>

<c:set var="now" value="<%=new java.util.Date()%>" />
Copyright &copy; <fmt:formatDate pattern="yyyy" value="${now}" /> My Company Name

Ant - Update at build time

copyright.xml

<project name="copyright" default="copyright">

<target name="init">
 <property name="application.properties.file" value="application.properties"/>
</target>


<target name="copyright" depends="init">
  <tstamp>
      <format property="copyright.year" pattern="yyyy"/>
  </tstamp>
  <echo>Copyright is: ${copyright.year}</echo>
  <propertyfile file="${application.properties.file}">
 <entry  key="app.copyright" value="Copyright © ${copyright.year} My Company Name"/>
  </propertyfile>
</target>

</project>

application.properties

app.copyright=Copyright © 2009 My Copyright message

#Mon Apr 26 11:15:54 PDT 2010
app.copyright=Copyright © 2010 My Company Name

How to use this script

PHP Application

<p>Copyright &copy; 2007 - <?php echo date('Y'); ?> My Company Name. All Rights Reserved.</p>

JavaScript

<p>Copyright &copy; <script language="JavaScript" type="text/javascript">document.write((new Date()).getFullYear());</script> My Company Name</p>

Wordpress

By PHP

<p>Copyright &copy; 2007 - <?php echo date('Y'); ?> My Company Name. All Rights Reserved.</p>

By JavaScript

<p>Copyright &copy; <script language="JavaScript" type="text/javascript">document.write((new Date()).getFullYear());</script> My Company Name</p>

Blogger

<p>Copyright &copy; <script language="JavaScript" type="text/javascript">document.write((new Date()).getFullYear());</script> My Company Name</p>

Please share your thoughts and suggestions in case you know a better way of doing the same thing.

Trying to run JAX-WS Sample Application in the Metro Environment

noreply@blogger.com (Sachin) — Fri, 22 Jan 2010 20:32:00 +0000

I recently downloaded the Metro 2.0 from https://metro.dev.java.net.

I wanted to install it on my Tomcat 6 (apache-tomcat-6.0.18) with JDK (1.6.0_10)

I followed Java example in the "Getting started with Metro" guide from https://metro.dev.java.net/getting-started/basic.html

Below are the issues I ran into during this process so thought of posting this for others benefit.

Issue #1 : Tomcat endorsed directory location in Ant build.xml

When you run the "server" target in build.xml it throws following error message.

C:\wsit-jaxws-fromjava>ant -Duse.tomcat=true server
Buildfile: build.xml

BUILD FAILED
C:\wsit-jaxws-fromjava\build.xml:129: C:\Tools\apache-tomcat-6.0.18\common\endorsed not found.

Total time: 0 seconds

This issue is due the wrong directory path for lib.endorsed in build.xml to fix this issue open the wsit-jaxws-fromjava\build.xml file and search for following

Change the directory value ${catalina.home}/common/endorsed to ${catalina.home}/endorsed as shown below and save the build.xml file.

Now run the "ant -Duse.tomcat=true server" command again, build should be successful.

Issue #2 : The xendorsed option is required for JDK6

Once the you are done generating the server side for this web service you need to generate the client sources for the same sample service.
When I run the "ant -Duse.tomcat=true client" command I get following error message and build is failed again.

C:\wsit-jaxws-fromjava>ant -Duse.tomcat=true client
Buildfile: build.xml
Trying to override old definition of task apt

setup:

generate-client:

BUILD FAILED
C:\wsit-jaxws-fromjava\build.xml:192: You are running on JDK6 which comes with JAX-WS 2.1 API, but this tool requires JAX-WS 2.2 API. Use the endorsed standards override mechanism (http://java.sun.com/javase/6/docs/technotes/guides/standards/), or set xendorsed="true" on .

Total time: 0 seconds

As the message says it clearly, this problem is due to the JDK6 being shipped with older version of JAX-WS API. To make the tag use a override on this you need to add one more attribute xendorsed="true" in the tag in Ant build.xml file.

Open the build.xml file and look for below tag


                    debug="${debug}"
            verbose="${verbose}"
            keep="${keep}"
            extension="${extension}"
            destdir="${build.classes.home}"
            wsdl="${client.wsdl}">

Now change this to add a new attribute as shown below.


                    debug="${debug}"
            xendorsed="true"
            verbose="${verbose}"
            keep="${keep}"
            extension="${extension}"
            destdir="${build.classes.home}"
            wsdl="${client.wsdl}">

Now run the "ant -Duse.tomcat=true client" command again, and this time it should generate all your client sources properly.

Issue #3 : Using the endorsed directory in JDK6

When I run the client using command "ant -Duse.tomcat=true run", it gives me below error.

C:\wsit-jaxws-fromjava>ant run
Buildfile: build.xml
Trying to override old definition of task apt

run:
     [java] Exception in thread "main" java.lang.NoSuchMethodError: javax.xml.ws.WebFault.messageName()Ljava/lang/String;
     [java]     at com.sun.xml.ws.model.RuntimeModeler.processExceptions(RuntimeModeler.java:1162)
     [java]     at com.sun.xml.ws.model.RuntimeModeler.processDocWrappedMethod(RuntimeModeler.java:898)
     [java]     at com.sun.xml.ws.model.RuntimeModeler.processMethod(RuntimeModeler.java:666)
     [java]     at com.sun.xml.ws.model.RuntimeModeler.processClass(RuntimeModeler.java:420)
     [java]     at com.sun.xml.ws.model.RuntimeModeler.buildRuntimeModel(RuntimeModeler.java:254)
     [java]     at com.sun.xml.ws.client.WSServiceDelegate.createSEIPortInfo(WSServiceDelegate.java:661)
     [java]     at com.sun.xml.ws.client.WSServiceDelegate.addSEI(WSServiceDelegate.java:649)
     [java]     at com.sun.xml.ws.client.WSServiceDelegate.getPort(WSServiceDelegate.java:343)
     [java]     at com.sun.xml.ws.client.WSServiceDelegate.getPort(WSServiceDelegate.java:326)
     [java]     at com.sun.xml.ws.client.WSServiceDelegate.getPort(WSServiceDelegate.java:308)
     [java]     at javax.xml.ws.Service.getPort(Service.java:92)
     [java]     at fromjava.client.AddNumbersImplService.getAddNumbersImplPort(AddNumbersImplService.java:72)
     [java]     at fromjava.client.AddNumbersClient.main(Unknown Source)
     [java] Java Result: 1

BUILD SUCCESSFUL
Total time: 2 seconds

-----------

The error message is due to client using older version of jaxws-ri which already bundled with the JDK6.
The annotation javax.xml.ws.WebFault in the rt.jar that ships with JDK1.6.0_X does not contain a messageName property
where as the javax.xml.ws.WebFault annotation that comes in the webservices-api.jar does contain this property.

To avoid this error you need to copy the \endorsed\webservices-api.jar file to /jre/lib/endorsed directory

if /jre/lib/endorsed directory does not exist in your system create it and copy the webservices-api.jar file here.

For more details on endorsed directory read details at http://java.sun.com/javase/6/docs/technotes/guides/standards/

Now run the command "ant run" you should see the successful output.

C:\Downloads\wsit-jaxws-fromjava\wsit-jaxws-fromjava>ant run
Buildfile: build.xml
Trying to override old definition of task apt

run:
     [java] Invoking addNumbers(10, 20)
     [java] The result of adding 10 and 20 is 30.
     [java]
     [java] Invoking addNumbers(-10, 20)
     [java] Caught AddNumbersException_Exception: Numbers: -10, 20

BUILD SUCCESSFUL
Total time: 1 second

Let me know if you face any other issue while following steps.

Playing with Java String Split Basics

noreply@blogger.com (Sachin) — Tue, 20 Oct 2009 00:06:00 +0000

This is a simple tutorial for java beginners who are struggling on the String split() method. I have seen many students wondering about how to split the string in java with the help of split() method.
In this tutorial I am trying to show some simple exercises which can be used for learning and understanding String split and few other methods.

Understanding the two flavors of split method

public String[] split(String regex) - This method splits the string based on the given regular expression and returns array of strings.

public String[] split(String regex,int limit) - This method splits the string based on the given regular expression and returns array of strings. The limit parameter controls the number of times the pattern is applied and therefore affects the length of the resulting array. If the limit n is greater than zero then the pattern will be applied at most n - 1 times, the array's length will be no greater than n, and the array's last entry will contain all input beyond the last matched delimiter. If n is non-positive then the pattern will be applied as many times as possible and the array can have any length. If n is zero then the pattern will be applied as many times as possible, the array can have any length, and trailing empty strings will be discarded.

So for example if you have a string ["This is a String"] then a) calling a split(" ") method (space as delimiter) on this string will convert it to an array of four strings [1] - This [2] - is [3] - a [4] - String a) calling a split(" ", 2) method on this string will convert it to an array of 2 strings [1] - This [2] - is a String

Simplest thing first - Using the split() method with one character delimiter

public static void  singleCharacterDelimiterTest() {
String str = "This,is,a,String";
String delimiter = ",";
String[] splitStrings = str.split(delimiter);
for (int i = 0; i < splitStrings.length; i++) {
System.out.println(splitStrings[i]);
}
}

How about using another string as a delimiter?

public static void  singleWordDelimiterTest() {
String str = "ThisWORDisWORDaWORDString";
String delimiter = "WORD";
String[] splitStrings = str.split(delimiter);
for (int i = 0; i < splitStrings.length; i++) {
System.out.println(splitStrings[i]);
}
}

[0] This
[1] is
[2] a
[3] String

How about using multiple characters as delimiter?

public static void  multiCharacterDelimiterTest() {
String str = "This,is:a;String";
String delimiter = ",|:|;";
String[] splitStrings = str.split(delimiter);
for (int i = 0; i < splitStrings.length; i++) {
System.out.println("[" + i + "] "+ splitStrings[i]);
}
}

[0] This
[1] is
[2] a
[3] String

How about using multiple words as delimiter?

public static void  multiWordDelimiterTest() {
String str = "ThisWORD1isWORD2aWORD3String";
String delimiter = "WORD1|WORD2|WORD3";
String[] splitStrings = str.split(delimiter);
for (int i = 0; i < splitStrings.length; i++) {
System.out.println("[" + i + "] "+ splitStrings[i]);
}
}

[0] This
[1] is
[2] a
[3] String

Keeping a watch on few special characters

public static void  specialCharaterDelimiterTest() {
String str = "This|is^a$String";
String delimiter = "\\||\\^|\\$";
String[] splitStrings = str.split(delimiter);
for (int i = 0; i < splitStrings.length; i++) {
System.out.println("[" + i + "] "+ splitStrings[i]);
}
}

[0] This
[1] is
[2] a
[3] String

http://www.regular-expressions.info/

String Split using Java 1.1 Style - Using StringTokenizer class

StringTokenizer is a legacy class which is part of JDK since version 1.1. The String Tokenizer class allows an application to break a string into tokens. The set of delimiters (the characters that separate tokens) may be specified either at creation time or on a per-token basis. StringTokenizer's nextToken() method can be used to produce exact same output, See below example code.

public static void splitByTokenizer() {
StringTokenizer st = new StringTokenizer("This,is:a;String",",:;");
while (st.hasMoreTokens()) {
System.out.println(st.nextToken());
}
}

The output of this method will be

This
is
a
String

The split() method has been introduced sice JDK version 1.4 and StringTokenizer use has been discouraged after that. Here is what Sun suggest in JDK 1.6 Javadocs "StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code. It is recommended that anyone seeking this functionality use the split method of String or the java.util.regex package instead." Let me know your comments/feedback on this tutorial.