Interview Questions On Java,Java EE

Core Java Interview Questions

noreply@blogger.com (Deepun) — Fri, 03 Apr 2015 15:38:00 +0000

Every year many thousand technocrats choose Java careers across the globe,after formally taking Java training classes,courses and/or Java certifications like SCJP etc.While appearing for technical interviews,these budding Java programmers face variety of technical questions, are asked to write code snippets to prove their mettle in relevant topics of Java.They are not only assessed on language basics but also on their familiarity with Java development tools, coding standards and guidelines,optimization of Java code,load tests,securing code through Java obfuscation and many more. It is their performance in these interviews which decides their career fate and is highly dependent on to-the-point and not too verbose answers.

Apart from technical questions, an interviewee faces a spate of personal questions as well.In post, Personal Interview Questions you will find variety of questions asked on personal front.In wired world, it is very important to know where your resources are lying and how credible are they.

This blog intends to provide a consolidated knowledge base for all netizens,budding Java Engineers or experienced ones, interested in Java technology.This blog will primarily focus on 'Core Java' related questions and later on advanced topics in Java EE space,Open source technologies and frameworks and more.At this point this is a nice idea to put a roadmap right away to put all these questions in an organized fashion. In order to access questions list on a particular topic,please click the links associated with it.It will open the questions list in the same browser window and in order to comeback to this page, while going through various posts, you have to click back button in your bowser window.Each answer for a question on various topics will open in a fresh window,while you are through with reading an answer,close the open window in order to comeback to the questions list.If you want to access Master List of Core Java Interview Questions then click here.In order to jump to recent posts straightaway, you can view a list of these in a widget box as shown below:

Java Language Fundamentals (Click Link To Access Questions' List)

Packages and their classes (Click Link To Access Questions' List)

Java and Database Access
JFC Swing
Collection APIs

Check more miscellaneous short questions on Core Java with short answers,here.

If you starve for more knowledge on Core Java,you may like to check out online e-books and other resources on Core Java or access all Online Java and Java EE resources. All suggestions,comments are welcome in order to make this space more productive and useful for all its audiences.

Read more on Core Java:
- Short Questions On Core Java
- Interview Questions on Java 5

Java EE,Open Source,Advanced Technologies Interview Questions

noreply@blogger.com (Deepun) — Thu, 02 Apr 2015 10:00:00 +0000

In continuation of earlier post on Java Interview Questions this post is focussed on interview questions in several Java EE technologies(erstwhile J2EE).Apart from Java EE, interview questions on most widely used open source technologies like Struts,Hibernate,Spring and Velocity and more will also be covered.

On constant requests by readers to put something on personal interview questions, consequently, you may like to read post on personal interview questions , prior talking about Java Enterprise Edition.

Sun Microsystems introduced Java EE 5 specification under JSR 244 and the final release was made public on May ,2006.Java EE has become a cornerstone technology for enterprise level web based solution development.It has more than three million downloads and more than twenty six vendors' application servers support this specification.It is significant to go through an introduction of Java EE 5 before jumping to questions list straightaway.You can capture essence of Java EE 5 here in detail.

If you directly want to access Master List of Java EE Interview Questions then click here.

The list of questions on various topics covered under Java EE hood is as follows(on the basis of different technologies covered under Java EE umbrella) :

Java EE 5(Click To Access Questions' List)
Java Servlets
Java Server Pages and JSP Standard Tag Libraries
Enterprise Java Beans
Java Message Services
Java APIs for XML Parsing
Java Connector Architecture
Java Mail
Java Transaction APIs

Open Source Technologies/Emerging Frameworks:
Struts
Hibernate Framework
Spring Framework
Velocity
Apache AXIS
Annotations or attributes based programming (xdoclet etc).
Aspect Oriented Programming (AOP).
EJB 3.0.
Inversion of Control (IOC) (Also known as Dependency Injection).
JavaServer Faces (JSF) framework.
Test Driven Development (TDD).

Architectures:
Service Oriented Architecture

Others
Java Design Patterns

If anyone of you has come across a very unique experience in terms of technical and personal questions asked, feel free to share your experience.

Keep sharing your resources for ongoing learning...

Learn more about Java EE, here.

Master List Of Core Java Questions

noreply@blogger.com (Deepun) — Mon, 02 Mar 2015 08:54:00 +0000

OOPS

What is an Object?

What is a Class?

What is OOAD?

What is Data Abstraction ?

What is Data Encapsulation?

What is the difference between Data Abstraction and Information Hiding?

What is Inheritance and what are different types of it?

Why Java uses Singly rooted hierarchy?

Why does Java not support Multiple Inheritance?

Why is Java not 100% pure OOP language?

What is Early Binding?

What is Polymorphism/Late Binding?

What is method overloading?

What is method overriding?

How is Java different from C++?

What is UML and how is it useful in designing large systems?

Is UML useful for procedural programming ?

What are different notations used in UML ?

What is a Use case and an Actor?

How to identify an Actor?

What is Generalization?

What is Association and how it maps into a Java class?

What is Aggregation and how it maps into a Java class?

What is Composition and how it maps into a Java class?

What is Dependency and how it maps into a Java class?

What is the purpose of State machine diagrams?

What are different kinds of Structure diagrams?

What are different kinds of Interaction diagrams?

What are different kinds of Behavior diagrams?

Java Fundamentals

What is a Java Virtual Machine (JVM)?

What is a JVM consisted of?

What is a class loader and what is its responsibilities?

What is heap and stack?

How is your Java program executed inside JVM?

What is Java class file's magic number?

How JVM performs Thread Synchronization?

How JVM performs Garbage Collection?

How to profile heap usage?

What will you do if VM exits while printing "OutOfMemoryError" and increasing max heap size doesn't help?

Should one pool objects to help Garbage Collector?Should one call System.gc() periodically?

An application has a lot of threads and is running out of memory, why?

If your program is I/O bound or running in native methods, do these activities engage JVM?

What is the difference between interpreted code and compiled code?

Why Java based GUI intensive program has performance issues?

What is 64 bit Java ?

What is the difference between JVM and JRE?

What are different primitive datatypes in Java?

What are expressions,statements and blocks in Java?

What is a transient variable?

What is the difference between the '&' operator and the '&&' operator?

Why main method of Java has public static void?

If you have static block, constructor and main method in Java file then what will be the sequence of method calls?

What are the command line arguments?

Does Java support multi dimensional arrays?

What are the restrictions for static method?

Why a abstract method cannot be static?

Is 'sizeof' a keyword?

What is the precedence of operators in Java?

How is an argument passed in Java methods?

What is the difference between class variable, member variable and automatic(local) variable?

When are static and non static variables of a class initialized?

Can shift operators be applied to float types?

What are different Java declarations and their associated rules?

What are Java Modifiers?

Explain final modifier.

Can you change the reference of the final object?

Can abstract class be instantiated?

When does the compiler insist that the class must be abstract?

Where can static modifiers be used?

What is static initializer code?

Can an anonymous class implement an interface and extend a class at the same time?

What are volatile variables?

Can protected or friendly features be accessed from different packages?

How many ways can one write an infinite loop?

When do you use 'continue' and 'break' statements?

What is the difference between 'while' and 'do while' loop?

What is an Assertion and why using assertion in your program is a good idea ?

Explain Assertions with a code exmaple.

How many forms of assertions we have?

When assertions should be avoided?

What situations are best suitable for implementing assertions?

What is Exception ?

What is a user-defined exception?

What do you know about the garbage collector?

Why Java does not support pointers?

Does garbage collection guarantee that a program will not run out of memory?

What is finally in Exception handling?

What can prevent the execution of the code in finally block?

Explain 'try','catch' and 'finally' blocks?

Define Checked and Unchecked exception.

What is the difference between an abstract class and an interface?

What is the use of interface?

What is serializable interface?

Does a class inherit constructors from its superclass?

What's the difference between constructors and other methods?

If the method to be overridden has access type 'protected', can subclass have the access type as 'private'?

If you use super() or this() in a constructor where should it appear in the constructor?

What modifiers may be used with an inner class that is a member of an outer class?

Can an inner class be defined inside a method?

What is an anonymous class?

What is a thread?

What is the difference between process and threads?

What are two types of multitasking?

What are two ways of creating threads in Java and why so?

How does multithreading take place on a computer with a single CPU?

How a Java object be locked for exclusive use by a given thread?

What is Synchronization?

Explain wait(),notify(), and notifyAll() methods?

What is a Daemon thread?

How a dead thread can be started?

What is the difference between String and StringBuffer?

How is '==' different from .equals() method in case of String objects?

Explain StreamTokenizer?

What is Collection?

Explain List,Set and Map.

What is the serialization?

What is the difference between Serializable and Externalizable interface?

What is memory leak?

Difference between ArrayList and Vector class?

What is the difference between Hashtable and HashMap?

What is JFC?

What is the difference between JFC Swing and AWT?

What is the base class for all swing components?

What are lightweight and heavyweight components ?

How can a GUI component handle its own events?

What is a Layout Manager and what are its different types and their advantages?

How are the elements of a GridBagLayout organized?

What are the problems faced by Java programmers in absence of layout managers?

Where the CardLayout is used?

What is the difference between GridLayout and GridBagLayout?

How will you add a panel to a frame?

What is the difference between Application and Applet?

Explain Lifecycle of the Applet and what is the order of method invocation in an applet?

What is the difference between Java class and bean?

What is difference between trusted and untrusted applet?

How do you set Java Library path programmatically?

Explain the usage of java.util.Date and more classes and APIs for date handling in Java?

JDBC

What is JDBC ?

What are four drivers available in JDBC?

How do you establish database connection using JDBC?

How do you connect to a MySql Database using JDBC?

What are the different types of Statements?

What is PreparedStatement and how is different from Statement?

What is the difference between executeQuery () and execute() ?

What is the difference between executeQuery () and executeUpdate()?

How do you call a stored procedure in Java?

What are new features from JDBC2.0 onwards?

How can a cursor move in scrollable result sets?

Differentiate TYPE_SCROLL_INSENSITIVE and TYPE_SCROLL_SENSITIVE?

How will you differentiate the following two ways of loading a database driver?

How can you display a particular web page from an applet?

How can you get the hostname on the basis of IP addres ?

How can you get an IP address of a machine from its hostname?

How do you know who is accessing your server?

What are different socket options?

What should I use a ServerSocket or DatagramSocket in my applications?

Master List Of Java EE,Open Source,Advanced Technologies Questions(Release I )

noreply@blogger.com (Deepun) — Sun, 01 Mar 2015 16:32:00 +0000

Servlets

What is a servlet? Explain its lifecycle.

What is the difference between CGI and servlets?

What is a middleware and what is the functionality of Webserver?

Can there be more than one instance of a servlet at one time ?

Why there are no constructors in servlets?

What is a Servlet Context?

What is meant by Session tell me something about HttpSession?

What is the difference between GenericServlet and HTTPServlet?

What is the difference between doGet and doPost methods of HttpServlet class?

Why do GenericServlet and HttpServlet class implement Serializable interface?

How will you pass values from HTML to the servlet?

Can you use System.exit in your servlet end code?

If my browser does not support Cookie and my server sends a Cookie instance what will happen?

Can you use System.exit in your servlet end code?

What is the difference in between encodeRedirectURL and encodeURL?

How do you make servlet thread-safe?

How do you communicate between applet and servlet?

JSP

What is the difference between Java Servlets and Java ServerPages (JSP)?

What is the difference between page directive 'include' and 'jsp include' action command?

What is the difference between 'jsp:forward' and HttpResponse.sendRedirect()?

What is the difference between 'include file=".."' and 'jsp:include page = ... '?

What are implicit objects in JSP?

Explain the life-cycle methods of JSP

Explain different constituents of JSP like comments,expressions,declarations,scriptlets.

Does JSP support XML pages creation?

How can I show various kind of documents to a web client from JSP's and/or servlets?

How will you handle runtime exceptions in your JSPs?

How can you prevent caching in JSP?

EJB

How EJB evolved over the years?

What are Entity Bean and Session Bean?

How is container managed entity bean created?

What is the difference between Container managed persistent and Bean managed persistent

What is the difference between ejbCreate() and ejbPostCreate() in EntityBean?

What are the services provided by the EJB container ?

What are new features of EJB3?

What is Connection Pooling? Is it advantageous?

What's difference between Servlet/JSP session and EJB session?

How is JDO(Java Data Object) different from VO(Value Object) ?

What is session facade?

EJB Transactions

What are Bean-Managed Transactions?

What are some tips for using bean-managed transaction demarcation?

What is JTS ?

What are transaction properties?

What are transaction attributes ? Which transaction attributes should I use in which situations?

How can you handle transaction isolation?

Struts Framework

What is Struts and how it helps in web development?

Explain Struts1.x in a nutshell?

What are the methods in Action class?

How you will handle errors and exceptions in Struts?

How does Validator framework work in Struts?

What is DispatchAction?

How to handle duplicate submits in Struts?(new)

Spring Framework

What is Spring framework

Why is Spring Framework needed anyway?

What do you understand by Inversion of Control/Dependency Injection?

What is BeanFactory?

Explain ApplicationContext in Spring framework.

What is Aspect Oriented Programming and how is it related with Spring?

What are the problems you have with JDBC and how does Spring framework help to resolve them?

Explain typical Bean life cycle in Spring Bean Factory Container

What are ORMs supported by Spring and how it integrates with Hibernate?

Java Message Service APIs

What is messaging and how is it different from RMI?

When is JMS needed?

How Does the JMS API Work with the Java EE Platform?

Explain JMS API Architecture.

Explain Point-to-Point Messaging Domain.

Explain Publish/Subscribe Messaging Domain.

Java Design Patterns

What are Design Patterns and why one needs them?

What are different types of design patterns?

What is Singleton Design Pattern?

What is difference between Abstract Factory and Factory Method design patterns?

Explain Adapter Design Pattern in Java

Explain Decorator Design Pattern in Java

Explain Facade Design Pattern in Java

Miscellaneous Core Java Questions With Short Answers

noreply@blogger.com (Deepun) — Sun, 01 Feb 2015 16:43:00 +0000

In a Java program, how can you divert program messages to the system console, but error messages, say to a file?

A. The class 'System has a variable out that represents the standard output, and the variable err that represents the standard error device. By default, they both point at the system console. This how the standard output could be re-directed:
```
Stream stream = new Stream(new FileOutputStream("error.txt"));
System.setErr(stream);
System.setOut(stream);
```
How do you know if an explicit object casting is needed?

A. In order to assign a superclass object to a variable of a subclass,one needs to do explicit casting. For example:
```
Person person;
Man man;
man = (Man)person;
```
While automatic casting happens when you typecast a subclass object as parent class object.

What's the difference between the methods sleep() and wait()

A. The code sleep(1000); puts thread aside for exactly one second. The code wait(1000), causes a wait of up to one second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.

Why would you use a synchronized block vs. synchronized method?

A. A synchronized blocks place locks for shorter periods than synchronized methods.

Can you write a Java class that could be used both as an applet as well as an application?

A. Yes. Add a main() method to the applet.

Can you call one constructor from another if a class has multiple constructors

A. Yes. Use this() syntax.

How will you convert a String array to an ArrayList object?

A.


String[] stringArray = new String[] {"x", "y", "Z"};
List list = Arrays.asList(stringArray);

Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written?

A. Yes, it does. The FileNoFoundException is inherited from the IOException. Exception's subclasses have to be caught first.

Can an inner class declared inside of a method access local variables of this method?

A. It's possible if these variables are final.

What can go wrong if you replace && with & in the following code:


String a=null;
if (a!=null && a.length()>10) {...}

A. A single ampersand here would lead to a NullPointerException.

When should the method invokeLater()be used?

A. To ensure that Swing components are updated through the event-dispatching thread.

What's the difference between a queue and a stack?

A. Stacks works by last-in-first-out rule (LIFO), while queues use the FIFO rule

You can create an abstract class that contains only abstract methods. On the other hand, you can create an interface that declares the same methods. So can you use abstract classes instead of interfaces?

A. Sometimes. But your class may be a descendant of another class and in this case the interface is your only option.

If you're overriding the method equals() of an object, which other method you might also consider?

A.hashCode()

You are planning to do an indexed search in a list of objects. Which of the two Java collections should you use: ArrayList or LinkedList?

A. ArrayList

How would you make a copy of an entire Java object with its state?

A. Have this class implement Cloneable interface and call its method clone().

How can you minimize the need of garbage collection and make the memory use more effective?

A. Use object pooling and weak object references.

There are two classes: A and B. The class B need to inform a class A when some important event has happened. What Java technique would you use to implement it?

A. If these classes are threads then consider notify() or notifyAll(). For regular classes one can use the Observer interface.

How will you sort a collection object?

A.

  
// Sort
Collections.sort(list);

// Case-insensitive sort
Collections.sort(list, String.CASE_INSENSITIVE_ORDER);

// Reverse-order sort
Collections.sort(list, Collections.reverseOrder  ());

// Case-insensitive reverse-order sort
Collections.sort(list, String.CASE_INSENSITIVE_ORDER);
Collections.reverse(list);

In a Java class, one has 10 variables. One wants to serialize only 3 variables,how can this be achieved?

A.Make variables as 'transient' which are not to be serialized.

Master List Of Code Snippets

noreply@blogger.com (Deepun) — Mon, 26 Jan 2015 14:18:00 +0000

XML Parsing Using SAX

File Operations

Experimenting with java.util.Date.

Using java.lang.reflect.* APIs

Using java.lang.Comparable.* interface

Thread Interruption

Get Locale Specific Date

Write Into An Excel File Using Java

Sending EMail To GMail SMTP Server Using Java Mail APIs

Some commonly used validations like EMail,Phone Number,SSN,Numeric values through Regular Expressions

Simplifying Service Oriented Architecture

noreply@blogger.com (Deepun) — Mon, 12 Jan 2015 05:35:00 +0000

What is SOA?

Why SOA?

What are the constituents of SOA?

Who suits best for SOA?

When to avoid implementation of SOA?

How to avoid risks in SOA implementation?

How SOA makes things better or even worse?

How to develop,test and maintain SOA based solutions?

How to register Web Services with UDDI4j?

Webservices, Apache Axis Way

Webserivces With Apache Axis Continued...

Apache AXIS with IBM's WSAD/RAD

How to persist the java objects using Hibernate ORM framework?

noreply@blogger.com (Deepun) — Wed, 04 Nov 2009 13:59:00 +0000

The answer to this question takes the form of a tutorial, where I will go in details, step by step. Hibernate reduces number of lines of coding/writing SQLs for persisting object into the database considerably. This takes focus from doing repetitive work to focus on implementing business logic to address a business problem.

Hibernate uses a object relation mapping file in form of an XML or properties file. In this file there exists a mapping between a Java object and corresponding database table.First thing first, let us create the needed environment to achieve our objective.

We need following tools and binaries:

1.The IDE used is Eclipse Galileo(latest one while writing this post).
2.Hibernate binaries(Hibernate Core 3.3.2 GA and Hibernate Tools 3.2.4 GA)can be downloaded from here
3.Database HSQLDB 1.9

The next step is unzip Hibernate Tools 3.2.4 GA and put features and plugins contents to features and plugins directory of Eclipse Galileo. Ensure you have closed Eclipse IDE prior to this step and once you are done with copying part then restart the Eclipse Galileo.

You have to ensure following JARs have been included in the project:

-hibernate3.jar(contains all core Hibernate files)

-antlr-2.7.6.jar

-commons-collections-3.1.jar

-dom4j-1.6.1.jar

-javassist-3.9.0.GA.jar

-jta-1.1.jar

-slf4j-api-1.5.8.jar(used for logging purposes)

-hsqldb.jar(used for connecting to HSQL Database)

Once all above steps are over then choose Hibernate perspective in Eclipse IDE.Go to Window-Open Perspective-Other and select Hibernate perspective as show in the image given below:

Next step is to define object relation mapping XML file which has .hbm.xml extension. First create a package named com.iqjava.employee and inside this package we will create a new OR mapping XML named 'employee.hbm.xml'.(Right click on package com.iqjava.employee, select New -Hibernate XML Mapping File)

having contents as given below:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.iqjava.employee.Employee" table="EMP">
<meta attribute="class-description">
This class contains the employee details.
</meta>
<id name="employeeId" type="long" column="EMP_ID">
<generator class="native"/>
</id>
<property name="employeeName" type="string" column="EMP_NAME" not-null="true" />
</class>
</hibernate-mapping>

In this OR Mapping file, class element depicts the class which will be mapped with an underlying table of RDBMS, in this case EMP table.The id element represents primary key of the table wherein attribute name represents a variable(employeeId) in Java class which is mapped with the column (attribute of id element) of the table(EMP_ID).

The type attribute represents the hibernate mapping type which will convert data from Java String type to underlying database String datatype .The generator element is used for automatically generate the primary key values.The native value of class attributes ascertain that hibernate picks either identity, sequence or hilo algorithm depending upon the capabilities of the underlying database. The property element is used to link a property in the Java class to a column in the database table.

The next step is to create Hibernate configuration file.Select 'src' folder, right click and choose New--Hibernate Configuration File menu option.

The following wizard window will appear and you will have to enter the data as shown in the picture given below:

The content of the Hibernate configuration file is shown as below:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">org.hsqldb.jdbcDriver</property>
        <property name="hibernate.connection.url">jdbc:hsqldb:hsql://localhost</property>
        <property name="hibernate.connection.username">sa</property>
        <property name="hibernate.dialect">org.hibernate.dialect.HSQLDialect</property>
        <property name="connection.password"></property>
        <property name="connection.pool_size">1</property>
        <property name="hibernate.dialect"> org.hibernate.dialect.HSQLDialect</property>
        <property name="show_sql">true</property>
        <property name="hbm2ddl.auto">create</property>
        <mapping resource="com/iqjava/employee/employee.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

Once you are done with this step then next step is to create a new a Hibernate console configuration. To do this right click the project folder, select New --- Hibernate Console Configuration.The following Wizard appears:

By default the wizard will load the Hibernate configuration file information. Just click the Finish button to create the Hibernate console configuration.
Once above step is done, you can generate code by selecting the Hibernate Code Generation Configurations option form Run option on toolbar as depicted below:

Once the Wizard shows up, please ensure following tabs have details according to images shown as below:

Once all these settings are ensured then hit Run button and you get Employee.java file being generated from .hbm.xml file and its contents are as shown below:

package com.iqjava.employee;

// Generated Nov 3, 2009 6:02:21 PM by Hibernate Tools 3.2.4.GA

/**
 * This class contains the employee details.
 */
public class Employee implements java.io.Serializable {

    private long employeeId;
    private String employeeName;

    public Employee() {
    }

    public Employee(String employeeName) {
        this.employeeName = employeeName;
    }

    public long getEmployeeId() {
        return this.employeeId;
    }

    public void setEmployeeId(long employeeId) {
        this.employeeId = employeeId;
    }

    public String getEmployeeName() {
        return this.employeeName;
    }

    public void setEmployeeName(String employeeName) {
        this.employeeName = employeeName;
    }

}

Now we create HibernateUtil.java file which creates a SessionFactory from the Hibernate configuration file. The implementation of HibernateUtil.java is given as below:

package com.iqjava.util;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
    private static final SessionFactory sessionFactory;
    static {
        try {
            sessionFactory = new Configuration().configure()
                    .buildSessionFactory();
        } catch (Throwable ex) {
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

The next step is to create an ExecutionClass.java. The implementation of this class is given as below:

package com.iqjava.employee;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import java.util.List;
import java.util.Iterator;
import com.iqjava.util.HibernateUtil;

public class ExecutionClass {

    public static void main(String[] args) {
        
        ExecutionClass obj = new ExecutionClass();
        Long empId1 = obj.saveEmployee("John");
        Long empId2 = obj.saveEmployee("Paul");
        Long empId3 = obj.saveEmployee("Bill");
        obj.listEmployee();
        System.out.println("Updating emp3....");
        obj.updateEmployee(empId3, "Michael");
        System.out.println("Deleting emp2....");
        obj.deleteEmployee(empId2);
        System.out.println("List employees....");
        obj.listEmployee();
    }
    
    public Long saveEmployee(String employeeName)
    {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = null;
        Long empId = null;
        try {
            transaction = session.beginTransaction();
            Employee emp = new Employee();
            emp.setEmployeeName(employeeName);
            empId = (Long) session.save(emp);
            transaction.commit();
        } catch (HibernateException e) {
            transaction.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }
        return empId;
    }
    
    public void listEmployee()
    {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = null;
        try {
            transaction = session.beginTransaction();
            List emps = session.createQuery("from Employee").list();
            for (Iterator iterator = emps.iterator(); iterator.hasNext();)
            {
                Employee emp = (Employee) iterator.next();
                System.out.println(emp.getEmployeeName());
            }
            transaction.commit();
        } catch (HibernateException e) {
            transaction.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }
    }
    
    public void updateEmployee(Long empId, String employeeName)
    {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = null;
        try {
            transaction = session.beginTransaction();
            Employee emp = (Employee) session.get(Employee.class, empId);
            emp.setEmployeeName(employeeName);
            transaction.commit();
        } catch (HibernateException e) {
            transaction.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }
    }
    
    public void deleteEmployee(Long empId)
    {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = null;
        try {
            transaction = session.beginTransaction();
            Employee emp = (Employee) session.get(Employee.class, empId);
            session.delete(emp);
            transaction.commit();
        } catch (HibernateException e) {
            transaction.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }
    }

}

The code details of the above are self explanatory.The project structure in Eclipse is depicted as shown below:

Before executing the ExecutionClass.java., please ensure you have started the HSQLDB server as depicted in image shown below

Once the code in ExecutionClass.java is executed then console of Eclipse IDE shows following output:


31 [main] INFO org.hibernate.cfg.Environment - Hibernate 3.3.2.GA
31 [main] INFO org.hibernate.cfg.Environment - hibernate.properties not found
47 [main] INFO org.hibernate.cfg.Environment - Bytecode provider name : javassist
47 [main] INFO org.hibernate.cfg.Environment - using JDK 1.4 java.sql.Timestamp handling
219 [main] INFO org.hibernate.cfg.Configuration - configuring from resource: /hibernate.cfg.xml
219 [main] INFO org.hibernate.cfg.Configuration - Configuration resource: /hibernate.cfg.xml
437 [main] INFO org.hibernate.cfg.Configuration - Reading mappings from resource : com/iqjava/employee/employee.hbm.xml
594 [main] INFO org.hibernate.cfg.HbmBinder - Mapping class: com.iqjava.employee.Employee -> EMP
625 [main] INFO org.hibernate.cfg.Configuration - Configured SessionFactory: null
750 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Using Hibernate built-in connection pool (not for production use!)
750 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Hibernate connection pool size: 1
750 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - autocommit mode: false
781 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - using driver: org.hsqldb.jdbcDriver at URL: jdbc:hsqldb:hsql://localhost
781 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - connection properties: {user=sa, password=****}
1140 [main] INFO org.hibernate.cfg.SettingsFactory - RDBMS: HSQL Database Engine, version: 1.9.0
1140 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC driver: HSQL Database Engine Driver, version: 1.9.0
1203 [main] INFO org.hibernate.dialect.Dialect - Using dialect: org.hibernate.dialect.HSQLDialect
1219 [main] INFO org.hibernate.transaction.TransactionFactoryFactory - Using default transaction strategy (direct JDBC transactions)
1219 [main] INFO org.hibernate.transaction.TransactionManagerLookupFactory - No TransactionManagerLookup configured (in JTA environment, use of read-write or transactional second-level cache is not recommended)
1219 [main] INFO org.hibernate.cfg.SettingsFactory - Automatic flush during beforeCompletion(): disabled
1219 [main] INFO org.hibernate.cfg.SettingsFactory - Automatic session close at end of transaction: disabled
1219 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC batch size: 15
1219 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC batch updates for versioned data: disabled
1219 [main] INFO org.hibernate.cfg.SettingsFactory - Scrollable result sets: enabled
1219 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC3 getGeneratedKeys(): enabled
1219 [main] INFO org.hibernate.cfg.SettingsFactory - Connection release mode: auto
1219 [main] INFO org.hibernate.cfg.SettingsFactory - Default batch fetch size: 1
1219 [main] INFO org.hibernate.cfg.SettingsFactory - Generate SQL with comments: disabled
1219 [main] INFO org.hibernate.cfg.SettingsFactory - Order SQL updates by primary key: disabled
1219 [main] INFO org.hibernate.cfg.SettingsFactory - Order SQL inserts for batching: disabled
1219 [main] INFO org.hibernate.cfg.SettingsFactory - Query translator: org.hibernate.hql.ast.ASTQueryTranslatorFactory
1234 [main] INFO org.hibernate.hql.ast.ASTQueryTranslatorFactory - Using ASTQueryTranslatorFactory
1234 [main] INFO org.hibernate.cfg.SettingsFactory - Query language substitutions: {}
1234 [main] INFO org.hibernate.cfg.SettingsFactory - JPA-QL strict compliance: disabled
1234 [main] INFO org.hibernate.cfg.SettingsFactory - Second-level cache: enabled
1234 [main] INFO org.hibernate.cfg.SettingsFactory - Query cache: disabled
1234 [main] INFO org.hibernate.cfg.SettingsFactory - Cache region factory : org.hibernate.cache.impl.NoCachingRegionFactory
1234 [main] INFO org.hibernate.cfg.SettingsFactory - Optimize cache for minimal puts: disabled
1234 [main] INFO org.hibernate.cfg.SettingsFactory - Structured second-level cache entries: disabled
1250 [main] INFO org.hibernate.cfg.SettingsFactory - Echoing all SQL to stdout
1250 [main] INFO org.hibernate.cfg.SettingsFactory - Statistics: disabled
1250 [main] INFO org.hibernate.cfg.SettingsFactory - Deleted entity synthetic identifier rollback: disabled
1250 [main] INFO org.hibernate.cfg.SettingsFactory - Default entity-mode: pojo
1250 [main] INFO org.hibernate.cfg.SettingsFactory - Named query checking : enabled
1359 [main] INFO org.hibernate.impl.SessionFactoryImpl - building session factory
1797 [main] INFO org.hibernate.impl.SessionFactoryObjectFactory - Not binding factory to JNDI, no JNDI name configured
1812 [main] INFO org.hibernate.tool.hbm2ddl.SchemaExport - Running hbm2ddl schema export
1812 [main] INFO org.hibernate.tool.hbm2ddl.SchemaExport - exporting generated schema to database
1812 [main] INFO org.hibernate.tool.hbm2ddl.SchemaExport - schema export complete
Hibernate: insert into EMP (EMP_ID, EMP_NAME) values (null, ?)
Hibernate: insert into EMP (EMP_ID, EMP_NAME) values (null, ?)
Hibernate: insert into EMP (EMP_ID, EMP_NAME) values (null, ?)
Hibernate: select employee0_.EMP_ID as EMP1_0_, employee0_.EMP_NAME as EMP2_0_ from EMP employee0_
John
Paul
Bill
Updating emp3....
Hibernate: select employee0_.EMP_ID as EMP1_0_0_, employee0_.EMP_NAME as EMP2_0_0_ from EMP employee0_ where employee0_.EMP_ID=?
Hibernate: update EMP set EMP_NAME=? where EMP_ID=?
Deleting emp2....
Hibernate: select employee0_.EMP_ID as EMP1_0_0_, employee0_.EMP_NAME as EMP2_0_0_ from EMP employee0_ where employee0_.EMP_ID=?
Hibernate: delete from EMP where EMP_ID=?
List employees....
Hibernate: select employee0_.EMP_ID as EMP1_0_, employee0_.EMP_NAME as EMP2_0_ from EMP employee0_
John
Michael

Check if the database schema is created and the data is inserted into the EMP table or not. Simply open a new command prompt, go to the hsqldb installed directory and type the following command.
java -cp ./lib/hsqldb.jar org.hsqldb.util.DatabaseManager
The dialog box as shown below pops up

and here select Type as "HSQL Database Engine Server" and click Ok.You see the HSQL Database Manager window as shown below, type the SQL as shown and press execute button. The result shown depicts data existing in the database.

One can exit from the database by typing 'shutdown' and hitting Execute button.

How is ANT Property Task used?

noreply@blogger.com (Deepun) — Thu, 08 Oct 2009 11:41:00 +0000

In order to to set the Ant properties, the <property> task is used. Once property value is set, it cannot be changed. It means they are immutable.In order to set a property to a specific value, the name and value pair is used.

Example

<property name="project.name" value="IQJava"/>

If you want to set a property to a location then name/location assignment is used.
To use the properties surround them with ${}.

Example

<property location="destination" name="dest.dir"/>
<property name="war.dir" location="${dest.dir}/${project.name}"/>

A build.xml as shown in following code box displays how effectively property tasks can be used within a build.xml:

<project basedir="." default="all">
    <property name="gensrc.dir" value="gen_src"/>
    <property name="release.dir" value="release"/>
    <property name="src.dir" value="../src"/>
    <property name="lib.dir" value="../externals/lib"/>
     <property name="class.dir" value="classes"/>
    <property name="class.dir.lib" value="${class.dir}/lib"/>
    <property name="class.dir.src" value="${class.dir}/src"/>
    
    <import file="one-jar-ant-task.xml"/> 
    <!-- Deletes the directories and files....-->
    <target name="clean">
        <delete dir="${gensrc.dir}"/>
        <delete dir="${class.dir}"/>
        <delete>
            <fileset dir="${lib.dir}" >
                <include name="**/xyz.jar"/>
            </fileset>
            <fileset dir="${release.dir}" >
                <include name="**/abc.jar"/>
            </fileset>
        </delete>    

    </target>
    <!-- Prepare the Directories needed for code generation -->
    <target name="prepare">
        <mkdir dir="${class.dir}"/>
        <mkdir dir="${gensrc.dir}"/>
        <mkdir dir="${class.dir.lib}"/>
        <mkdir dir="${class.dir.src}"/>
    </target>
    
    <!-- Compile the source code available in src folder -->
    <target name="compilesrc">
        <javac srcdir="${src.dir}" destdir="${class.dir.src}" target="1.4" source="1.4"
            debug="off" deprecation="on" optimize="off" encoding="iso-8859-1">
            <classpath >
                 <fileset dir="${lib.dir}" includes="**/*.jar"/>
            </classpath>
        </javac>
        <copy todir="${class.dir.src}">
            <fileset dir="${src.dir}" includes="*.properties"/>
        </copy>
    </target>

    <!-- Generate the lib jar file -->
    <target name="lib">
        <jar manifest="manifest.mf" destfile="${lib.dir}/xyz.jar" includes="**/*.class" basedir="${class.dir.lib}" />
    </target>
</project>

How to integrate ANT tool with Eclipse IDE?

noreply@blogger.com (Deepun) — Thu, 08 Oct 2009 10:21:00 +0000

ANT Eclipse IDE(latest edition of Eclipse IDE is Galileo) integration is a very simple process as summarized in following steps:

1. As a first step, create a Java Project in Eclipse IDE.

2. Associate a build.xml with this project and ensure you put this XML at the same location as shown in package structure in Eclipse IDE :
(Click images to enlarge)

The code of build.xml is as given below:

<?xml version="1.0" ?> 
<project name="IQJava" default="execute">

    <target name="init" depends="clean">
        <mkdir dir="build/classes" />
    </target>

    <target name="compile" depends="init">
        <javac srcdir="src" destdir="build/classes" />
    </target>
    
    <target name="execute" depends="compile">
        <java classname="com.iqjava.ant.AntExample" classpath="build/classes" />
    </target>

    <target name="clean">
        <delete dir="build" />
    </target>
    
</project>

3. Run this build XML

4. The output of this execution will look like as given below:

What is ANT and how can one configure it?

noreply@blogger.com (Deepun) — Wed, 07 Oct 2009 16:38:00 +0000

ANT is a Java based build tool and helps in automating whole of build process of a Java project.
ANT uses an XML build file and by default it looks for a build file named build.xml from the directory it has been executed.

A build.xml contains several targets e.g. creating or deleting directory structure, post compilation creation of jar or ear files, extracting/unzipping jar/ear files etc.One target can depend upon one or more targets and it can contain one or more tasks.

One can download Apace Ant 1.7.1 from here.Once that is done, extract it any of your local drive. Set the system variables as follows:

ANT_HOME =D:\apache-ant-1.7.1 (Here I have extracted the ANT ZIP at D drive)
PATH = %ANT_HOME%\bin

To ensure proper installation of ANT, go to command prompt and execute the command "ant - version", you will see the installed ant version.

The execution of ANT file is done from the directory where build.xml resides and simply typing ant command on console and hit enter will start the execution of build file.

The build.xml looks like as given below:
<?xml version="1.0" ?>

<project name="IQJava" default="compress">

    <target name="compile">
        <javac srcdir="com/iqjava/log4j"/>
        <echo> Compilation Complete! </echo>
    </target>
    
    <target name="compress" depends="compile">
            <jar destfile="IQJava.jar" basedir="." includes="*.class" />
            <echo> Building .jar file Complete! </echo>
    </target>

</project>

In the build.xml,<project> element is the root element, name attribute of this represents the name of the project.

<target> element can exist multiple times within project element and each one of them represents a single stage. In the above build.xml, we have compile target element which contains two tasks, one - <echo> and the other <javac> which builds java files.

The other target element 'compress' is dependent upon compile target element. It creates a jar file which includes all the .class files in current directory.

The echo tasks just display messages on console.

How do you configure log4j with XML?

noreply@blogger.com (Deepun) — Mon, 05 Oct 2009 15:29:00 +0000

This configuration of log4j with XML consists of following files:

a.XMLLog4jExample.java
b.log4j.xml

XMLLog4jExample.java

package com.iqjava.log4j;

import org.apache.log4j.Logger;
import org.apache.log4j.xml.DOMConfigurator;

public class XMLLog4jExample {
    static final Logger logger = Logger.getLogger(XMLLog4jExample.class);
    

    public static void main(String[] args) {
        DOMConfigurator.configure("log4j.xml");
        logger.debug("This is a debug message");
        logger.info("This is an info message");
        logger.warn("This is a warn message");
        logger.error("This is an error message");
        logger.fatal("This is a fatal message");

    }
}

log4j.xml looks like:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j='http://jakarta.apache.org/log4j/'>
    <appender name="CA" class="org.apache.log4j.ConsoleAppender">
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%-4r [%t] %-5p %c %x - %m%n" />
        </layout>
    </appender>
    <root>
        <level value="debug" />
        <appender-ref ref="CA" />
    </root>
</log4j:configuration>

Here goes the output of the program:

0    [main] DEBUG com.iqjava.log4j.XMLLog4jExample  - This is a debug message
2    [main] INFO  com.iqjava.log4j.XMLLog4jExample  - This is an info message
2    [main] WARN  com.iqjava.log4j.XMLLog4jExample  - This is a warn message
2    [main] ERROR com.iqjava.log4j.XMLLog4jExample  - This is an error message
2    [main] FATAL com.iqjava.log4j.XMLLog4jExample  - This is a fatal message

Eclipse project structure is depicted as in diagram given below:

How to log different modules in different log files?

noreply@blogger.com (Deepun) — Fri, 02 Oct 2009 16:35:00 +0000

Logging messages from different modules in different log files are commonly expected in a project.One can create as many loggers specific to different modules/packages inside the log4j properties file.

As for instance, we want to log workflow related log messages into a file named workflow.log while services related logs into a file named services.log.

The log4j.properties file will describe two seperate FileAppenders and each of them is associated with individual package.The log4j.properties file as shown below depicts two FileAppenders:

log4j.rootLogger=DEBUG

# WorkflowFileAppender - logs messages in the workflow.log file.
log4j.appender.WorkflowFileAppender=org.apache.log4j.FileAppender
log4j.appender.WorkflowFileAppender.File=workflow.log
log4j.appender.WorkflowFileAppender.layout=org.apache.log4j.PatternLayout
log4j.appender.WorkflowFileAppender.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

# ServicesFileAppender - logs messages in the services.log file.
log4j.appender.ServicesFileAppender=org.apache.log4j.FileAppender
log4j.appender.ServicesFileAppender.File=services.log
log4j.appender.ServicesFileAppender.layout=org.apache.log4j.PatternLayout
log4j.appender.ServicesFileAppender.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

log4j.logger.com.iqjava.workflow=,WorkflowFileAppender 
log4j.logger.com.iqjava.services=,ServicesFileAppender

Here the root logger is set as 'DEBUG' which is just for information purpose, and not necessary.We have not set any logger level with individual file appenders. They both have been left blank so that rootLogger level would be inherited.We can surely change that if we want.

The code snippet contains two java files:

1. WorkflowExample.java

package com.iqjava.workflow;

import org.apache.log4j.Logger;
import org.apache.log4j.PropertyConfigurator;

public class WorkflowExample {

    static Logger logger = Logger.getLogger(WorkflowExample.class);

    public static void main(String[] args) {

        PropertyConfigurator.configure("log4j.properties");
        logger.debug("Here goes the debug message");
        logger.error("Here goes the error message");
        logger.fatal("Here goes the fatal message");
        logger.info("Here goes the info message");
        logger.warn("Here goes the warn message");

    }

}

2.ServicesExample.java

package com.iqjava.services;

import org.apache.log4j.Logger;
import org.apache.log4j.PropertyConfigurator;

public class ServicesExample {
    
    static Logger logger = Logger.getLogger(ServicesExample.class);

    public static void main(String[] args) {

        PropertyConfigurator.configure("log4j.properties");
        logger.debug("Here goes the debug message");
        logger.error("Here goes the error message");
        logger.fatal("Here goes the fatal message");
        logger.info("Here goes the info message");
        logger.warn("Here goes the warn message");

    }

}

If the individual java appenders are executed then output of workflow.log and services.log will look like as given below:

3.workflow.log

0    [main] DEBUG com.iqjava.workflow.WorkflowExample  - Here goes the debug message
33   [main] ERROR com.iqjava.workflow.WorkflowExample  - Here goes the error message
33   [main] FATAL com.iqjava.workflow.WorkflowExample  - Here goes the fatal message
33   [main] INFO  com.iqjava.workflow.WorkflowExample  - Here goes the info message
34   [main] WARN  com.iqjava.workflow.WorkflowExample  - Here goes the warn message

4.services.log

0    [main] DEBUG com.iqjava.services.ServicesExample  - Here goes the debug message
1    [main] ERROR com.iqjava.services.ServicesExample  - Here goes the error message
1    [main] FATAL com.iqjava.services.ServicesExample  - Here goes the fatal message
2    [main] INFO  com.iqjava.services.ServicesExample  - Here goes the info message
2    [main] WARN  com.iqjava.services.ServicesExample  - Here goes the warn message

If you want to change the logger level for these file appenders, you can always do that in log4j.properties file.

Log4j Configuration With properties file

noreply@blogger.com (Deepun) — Sun, 27 Sep 2009 12:37:00 +0000

Log4j configuration can be done either using an XML or a properties file externally. This makes your code independent of logging related steps to be followed in your code, so no ongoing source code modifications.

All you require to achieve that are logger, appender and layout. The logger object is used to do logging, appender decides where you want to append logging messages, to a console or to a file and finally layout decides on format, the way you want logging messages to be logged.

In the previous post, where BasicConfigurator.configure() is used, the default appender ConsoleAppender and layout PatternLayout are in use.

First of all the contents of log4j.properties file looks like:

log4j.rootLogger=ERROR, CA

log4j.appender.CA=org.apache.log4j.ConsoleAppender

log4j.appender.CA.layout=org.apache.log4j.PatternLayout
log4j.appender.CA.layout.ConversionPattern=%-1r [%t] %-5p %c %x - %m%n

And now the ExampleLog4j.java file:

package com.iqjava.log4j;

import org.apache.log4j.Logger;
import org.apache.log4j.PropertyConfigurator;

public class ExampleLog4j {


    static final Logger logger = Logger.getLogger(ExampleLog4j.class);
    
    public static void main(String[] args) {
        
        PropertyConfigurator.configure("log4j.properties");
        logger.debug("Here goes the debug message");
        logger.error("Here goes the error message");
        logger.fatal("Here goes the fatal message");
        logger.info("Here goes the info message");
        logger.warn("Here goes the warn message");
    }
}

To make things simpler for you, here is a snapshot from my Eclipse Galileo project:

The log4j levels follow the following order.
DEBUG
INFO
WARN
ERROR
FATAL

As the code level mentioned in .properties file is ERROR, it displays ERROR and FATAL messages only in result displayed of the code. If the code level would have been DEBUG then, all the messages would have been displayed on the console.

The result of the code looks like as given below:

0 [main] ERROR com.iqjava.log4j.ExampleLog4j  - Here goes the error message
2 [main] FATAL com.iqjava.log4j.ExampleLog4j  - Here goes the fatal message

What is Log4j and how can it be configured?

noreply@blogger.com (Deepun) — Sun, 27 Sep 2009 09:34:00 +0000

Log4j is a Java based open source logging service by Apache which is available with no cost to the public.The latest edition at the time of writing this post is log4j 2.0 for logging services designed for Java 5 and later.

The insertion of logging comments help in better management of debugging of code specially if the application is distributed and enterprise in nature. The proper usage of logger levels namely DEBUG, INFO, WARN, ERROR and FATAL can help developers analyzing proper functioning of the code.

A simple log4j configuration is explained with a code sample given below, here important is that log4j runtime jar(log4j-1.2.15.jar) is included in the classpath of your application in order to execute the following code:

package com.iqjava.log4j;

import org.apache.log4j.BasicConfigurator;
import org.apache.log4j.Logger;

public class ExampleLog4j {


    static final Logger logger = Logger.getLogger(ExampleLog4j.class);
    
    public static void main(String[] args) {
        BasicConfigurator.configure();
        logger.debug("Here goes the debug message");
        logger.error("Here goes the error message");
        logger.fatal("Here goes the fatal message");
        logger.info("Here goes the info message");
        logger.warn("Here goes the warn message");
    }
}

The output of the above code looks as given below:

0 [main] DEBUG com.iqjava.log4j.ExampleLog4j  - Here goes the debug message
2 [main] ERROR com.iqjava.log4j.ExampleLog4j  - Here goes the error message
2 [main] FATAL com.iqjava.log4j.ExampleLog4j  - Here goes the fatal message
2 [main] INFO com.iqjava.log4j.ExampleLog4j  - Here goes the info message
2 [main] WARN com.iqjava.log4j.ExampleLog4j  - Here goes the warn message

The numbers in the beginning of the output represents time elapsed from the beginning of the execution of the code in milliseconds, thread name, logger level and then log message.

The other logging configuration using log4j is with properties or XML file.Watch out for the next post, it will be related to that.

Velocity With XML

noreply@blogger.com (Deepun) — Wed, 23 Sep 2009 14:34:00 +0000

In this post, a code snippet describing a basic integration of XML with Velocity framework. Please ensure all runtime jar files associated with Velocity and Xerces XML parser are in your build path.

The following files are part of this code snippet;

1.XMLVelocityExample.java
2.xml.vm
3.book.xml

Here goes the Java code i.e. XMLVelocityExample.java:

import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.Velocity;

import org.jdom.Document;

import org.jdom.input.SAXBuilder;

import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.io.Writer;


public class XMLVelocityExample {
    public XMLVelocityExample(String templateFile) {
        Writer writer = null;

        try {
            Velocity.init();

            SAXBuilder builder;
            Document root = null;

            try {
                builder = new SAXBuilder("org.apache.xerces.parsers.SAXParser");
                root = builder.build("book.xml");
            } catch (Exception exception) {
                exception.printStackTrace();
            }

            VelocityContext context = new VelocityContext();
            context.put("root", root);

            Template template = Velocity.getTemplate(templateFile);

            writer = new BufferedWriter(new OutputStreamWriter(System.out));
            template.merge(context, writer);
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            if (writer != null) {
                try {
                    writer.flush();
                    writer.close();
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) {
        XMLVelocityExample test = new XMLVelocityExample("xml.vm");
    }
}

xml.vm looks like:

#macro ( recursive $xml $indent )     
#if( $xml.getChildren().size() > 0 )
$indent <$xml.getName()> 
#foreach ($child in $xml.getChildren() ) 
#recursive( $child "$indent  " )
#end
$indent </$xml.getName()>
#else
$indent <$xml.getName()>
$indent    $xml.getTextTrim()
$indent </$xml.getName()>
#end
#end

#set($i = " ")

Here goes document tree with a recursive Velocity macro :

#recursive( $root.getRootElement() $i )


Now accessing data directly :

email : $root.getRootElement().getChild("properties").getChild("author").getChild("email").getText()
last name :  $root.getRootElement().getChild("properties").getChild("author").getChild("name").getChild("fullname").getText()

book.xml file looks like:

<?xml version="1.0" encoding="UTF-8"?>
<document>
  <properties>
    <author>
    <email>sunnyg@sunnyg.com</email>
    <name>
       <lastname>
        Gavaskar
       </lastname>
       <first>
        Sunil
       </first>
       <fullname>Sunil Gavaskar</fullname>
        
    </name>
    </author>
    <title>
       Sunny Days
    </title>
  </properties>

  <body>
    Sunny within a body.
  </body>
</document>

This is how output looks like:

Here goes document tree with a recursive Velocity macro :

  <document> 
    <properties> 
      <author> 
        <email>
           sunnyg@sunnyg.com
        </email>
        <name> 
          <lastname>
             Gavaskar
          </lastname>
          <first>
             Sunil
          </first>
          <fullname>
             Sunil Gavaskar
          </fullname>
        </name>
      </author>
      <title>
         Sunny Days
      </title>
    </properties>
    <body>
       Sunny within a body.
    </body>
  </document>


Now accessing data directly :

email : sunnyg@sunnyg.com
last name :  Sunil Gavaskar

EMailing Through Velocity Framework

noreply@blogger.com (Deepun) — Thu, 17 Sep 2009 13:50:00 +0000

Velocity Framework helps in creating a pre-formatted template based email response mechanism. The code snippet in this post elaborates how one can use this feature from Velocity framework.

While running this application, ensure you have all required Velocity framework related library classes/jars in you project build path.

Here the code is distributed in following java files:

1.EMailer.java
2.EMailClient.java
3.Customer.java
4.Order.java

Template file:
5.email.vm

Here goes:

1. EMailer.java

import java.io.StringWriter;
import java.util.HashMap;
import java.util.Properties;

import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.VelocityEngine;
import org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader;


public class Emailer
{
    /**
     * Field description
     *
     * @since 1.0
     */
    VelocityEngine engine = new VelocityEngine();

    /**
     * Constructor description.
     *
     * @throws Exception Description
     */
    public Emailer() throws Exception
    {
        configure(engine);
    }

    /**
     * "Sends" (actually writes to System.out for demonstration  purposes) a
     * receipt e-mail for the specified order.
     *
     * @param order Description
     */
    public void sendReceipt(Order order) throws Exception
    {
        Template template = engine.getTemplate("email.vm");
        VelocityContext context = createContext();
        context.put("order", order);

        StringWriter writer = new StringWriter();
        template.merge(context, writer);
        writer.close();
        System.out.println("To: " + order.getCustomer().getEmail());
        System.out.println("Subject: " + context.get("subject"));
        System.out.println(writer.getBuffer());
    }

    /**
     * Configures the engine to use classpath to find templates
     *
     * @param engine Description
     */
    private void configure(VelocityEngine engine) throws Exception
    {
        Properties props = new Properties();
        props.setProperty(VelocityEngine.RESOURCE_LOADER, "classpath");
        props.setProperty("classpath." + VelocityEngine.RESOURCE_LOADER +
                          ".class",
                          ClasspathResourceLoader.class.getName());
        engine.init(props);
    }
    /**
      * Creates a Velocity context and adds a formatter tool
      * and store information.
      */
     private VelocityContext createContext() {
       VelocityContext context = new VelocityContext();
       context.put("formatter", new Formatter());

       HashMap store = new HashMap();
       store.put("name", "Amazon.com Bookstore");
       store.put("url", "http://amazon.comm");

       context.put("store", store);
       return context;
     }
}

2.EMailClient.java

import java.util.ArrayList;


public class EmailClient {
    /**
     * Example usage of Emailer functionality
     *
     * @param args Description
     */
    public static void main(String[] args) throws Exception {
        Emailer emailer = new Emailer();

        ArrayList lineItems = new ArrayList();
        lineItems.add(new Item("Thinking in Java", 24.05f));
        lineItems.add(new Item("Core Java Volume I", 34.30f));

        Customer customer = new Customer("John", "Brown", "jb@gmail.com");

        emailer.sendReceipt(new Order(customer, lineItems));
    }
}

3.Customer.java

public class Customer
{

    private String firstName;

    private String lastName;

    private String email;

    /**
     * Constructor 
     */
    public Customer(String firstName, String lastName, String email)
    {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }
    public String getFirstName()
    {
        return firstName;
    }
    public String getLastName()
    {
        return lastName;
    }
    public String getEmail()
    {
        return email;
    }
    public String getId()
    {
        return "" + firstName.charAt(0) + lastName.charAt(0);
    }
}

4. Order.java

import java.util.Date;
import java.util.Iterator;
import java.util.List;



public class Order
{
    private Customer customer;
    private List lineItems;
    private String orderNumber;

    public Order(Customer customer, List lineItems)
    {
        this.customer = customer;
        this.lineItems = lineItems;

        orderNumber = customer.getId() + "-" + new Date().getTime();
    }

    public Customer getCustomer()
    {
        return customer;
    }

    public List getLineItems()
    {
        return lineItems;
    }

    public String getOrderNumber()
    {
        return orderNumber;
    }

    public float total()
    {
        float total = 0;

        for (Iterator iterator = lineItems.iterator(); iterator.hasNext();)
        {
            Item item = (Item)iterator.next();
            total += item.getCost();
        }

        return total;
    }
}

5. email.vm file

 #set ($customer = ${order.customer})
 #macro(currency $amount)${formatter.currency($amount)}#end
 #macro(pad $string)${formatter.pad($string, 30)}#end
 #macro(description $item)#pad($item.description)#end

 ${customer.firstName},

 Thank you for your purchase.
 Your order number is ${order.orderNumber}.

 #pad("Description") Cost
 #foreach ($item in ${order.lineItems})
 #description($item) #currency(${item.cost})

 #end

 #pad("Total") #currency($order.total())


 Visit us again at ${store.url}!

 #set ($subject="${store.name} receipt")

This is how the result looks like:

To: jb@gmail.com
Subject: Amazon.com Bookstore receipt

 John,

 Thank you for your purchase.
 Your order number is JB-1253195547000.

 Description                    Cost
  Thinking in Java               $24.05
  Core Java Volume I             $34.30

 Total                          $58.35

 Visit us again at http://amazon.comm!

Objects and Java Building Object-Oriented, Multi-Threaded Applications with Java by Bill Venners

noreply@blogger.com (Deepun) — Tue, 08 Sep 2009 10:14:00 +0000

A book which is in HTML format and slight draw back is that you have to be online to go through the contents of the book or you just store all HTML pages of this book.If that does not bog you much, a fascinating book by Bill Venners who has also written 'Inside Java Virtual Machine'.

No PDF is available.

Read online...

Sams Teach Yourself Java 2 in 24 Hours

noreply@blogger.com (Deepun) — Tue, 08 Sep 2009 10:13:00 +0000

Sams Teach Yourself Java in 24 Hours is a step-by-step tutorial that teaches someone with no previous programming experience how to create simple Java programs and applets.

No PDF is available.

Read online...

Thinking In Java by Bruce Eckel,Ist,IInd and IIIrd Editions

noreply@blogger.com (Deepun) — Tue, 08 Sep 2009 10:12:00 +0000

Thinking in Java is a printed version of Bruce Eckel's online materials that provides a useful perspective on mastering Java for those with previous programming experience. The author's take on the essence of Java as a new programming language and the thorough introduction to Java's features make this a worthwhile tutorial.

Thinking in Java begins in a beautiful way to keep an interest of its readers like a suspense thriller...:-), with the author's reflections on why Java is new and better. The author outlines his thoughts on why Java will make you a better programmer, without all the complexity. The book is better when he presents actual language features.

PDF is available.

Download...

The Java Tutorial IIIrd Edition

noreply@blogger.com (Deepun) — Tue, 08 Sep 2009 10:12:00 +0000

Whether you're taking a class or learning on the job, The Java Tutorial, Third Edition, is a hands-on guide that lets you quickly become proficient with the Java programming language. Written by members of the Java Software team at Sun Microsystems, the book uses an interactive approach to help you learn the Java platform by example.
Since it's first online release in 1995, the material in The Java Tutorial has been updated continuously to reflect reader feedback and new releases of the Java platform. This third edition has been thoroughly updated to cover v1.3 of the Java Platform, Standard Edition, as well as preceding versions as early as JDK 1.1.

No PDF is available.

Read online...

The Java Tutorial Continued

noreply@blogger.com (Deepun) — Tue, 08 Sep 2009 10:10:00 +0000

The Java Tutorial Continued provides accurate, up-to-date coverage of features added to the original core Java platform. Written by the experts, The Java Tutorial Continued employs a hands-on, self-paced, example-driven approach. This book concentrates on JDK 1.2 APIs but also contains the information you need to use the JDK 1.1 versions of the APIs.

The tutorial books, including this book and The Java Tutorial, are the definitive programmers' guides to the core JDK. This book covers a broad spectrum of JDK features, including:

-The Java Collections Framework
-Internationalization
-2D Graphics and Sound
-JavaBeans(tm)
-IDL (Interface Definition Language), which adds CORBA capabilities to the Java platform
-Database connectivity through the JDBC(tm)
-RMI (Remote Method Invocation)
-Security
-JNI (Java Native Interface)
-Reflection
-Other topics such as JAR, the Standard Extension Mechanism, and Servlets

No PDF is available.

Read online...

Introduction To Programming Using Java

noreply@blogger.com (Deepun) — Tue, 08 Sep 2009 10:09:00 +0000

A free, on-line textbook on introductory programming, which uses Java as the language of instruction. This book is directed mainly towards beginning programmers, although it might also be useful for experienced programmers who want to learn something about Java. It is certainly not meant to provide complete coverage of the Java language.

The fifth edition covers Java 5.0. You will find many Java applets on the web pages that make up this book, and many of those applets require Java 5.0 or higher to function. Earlier editions, which covered earlier versions of Java, are still available; see the preface for links.

PDF version of this book is available.

Download...

A Java GUI Programmer's Primer

noreply@blogger.com (Deepun) — Tue, 08 Sep 2009 10:06:00 +0000

This book contains an introduction to the systematic development of Graphical User Interfaces (GUIs) using the Java environment. It does not attempt to introduce the Java language and it is assumed that the reader has some familiarity with Object Oriented Development (OOD) and its practical expression in Java.

Read online...

The Java Swing Tutorial

noreply@blogger.com (Deepun) — Tue, 08 Sep 2009 10:05:00 +0000

The Java(tm) Tutorial, is a guide to using the new Swing components, which are provided by the Java Foundation Classes (JFC). Developed and co-written by the lead writer on the Swing team, this book covers everything you need to know to write GUIs that use Swing components. The JFC Swing Tutorial uses a task-oriented, example-driven approach to introduce you to fundamental concepts and applications.
Designed to be read either cover-to-cover or as a quick reference, this book explains how to use each Swing component, perform layout, do basic drawing, and convert 1.1 AWT programs to Swing. This book covers Swing 1.1.1, which is available both as an extension to JDK(tm) 1.1 and as a core part of the Java(R) 2 Platform.

Read Online...