My Cute Blog

Convert Java LocalDateTime to ZonedDateTime

Sadupa Wijeratne — Fri, 17 Feb 2023 15:02:27 +0000

Here is how you can convert Java LocalDateTime to ZonedDatime.

Java LocalDateTime store only date time information without any timezone information. You can convert it to a ZonedTime with time zone information.

ZonedDateTime zonedDateTime = localDateTime.atZone(ZoneId.systemDefault())
          .withZoneSameInstant(ZoneOffset.UTC);

My Cute Blog.

Fix for hibernate Legacy-style query parameters no longer supported

Sadupa Wijeratne — Thu, 23 Jan 2020 07:08:18 +0000

You may have encountered following error if you are migrating hibernate to version 5.x from an older version,

org.hibernate.QueryException: Legacy-style query parameters (`?`) are no longer supported; use JPA-style ordinal parameters (e.g., `?1`) instead

This happens due to changes in hibernate HQL parameters of latest versions. Here is a quick fix to overcome this issue

Simply replace ‘?’ with ‘?0’ in your HQL query. For example consider following query,

from Customer where id= ?

You may fix this query as below,

from Customer where id= ?0

My Cute Blog.

How to setup Lets Encrypt SSL on Amazon Linux

Sadupa Wijeratne — Tue, 20 Aug 2019 12:56:10 +0000

Here is a step by step guide on how to setup Lets Encrypt free SSL certificate on an AWS EC2 instance with Amazon linux OS. Cerbot client is used to generate the certificates.

Currently Lets Encrypt does not officially supports for Amazon Linux OS. But you can use Certbot client in debug mode to install a free SSL certificate on your AWS EC2 instance.

Installing Certbot client

Execute following commands to install Certbot client

wget https://dl.eff.org/certbot-auto
sudo mv certbot-auto /usr/local/bin/certbot-auto
sudo chown root /usr/local/bin/certbot-auto
sudo chmod 0755 /usr/local/bin/certbot-auto

Generating a SSL certificate from Lets Encrypt using Certbot

Execute following command to generate a SSL certificate from Lets Encrypt. Make sure to replace your website path and domain.

sudo /usr/local/bin/certbot-auto certonly --debug --webroot -w /var/www/html/ -d

First of all this command installs a set of libraries in your AWS EC2 instance which are required to generate SSL certificates.

Make sure to provide a valid email address during the process to ensure you get email alerts from Lets Encrypt regarding the status of your SSL certificate.

Finally certbot will generate certificate files required to enable SSL on your website. You may find them in following path,

/etc/letsencrypt/live//

privkey.pem : the private key for your certificate.
fullchain.pem: the certificate file used in most server software.
chain.pem : used for OCSP stapling in Nginx >=1.3.7.
cert.pem : server certificate

Configuring Apache web server to use SSL certificates

Next we have to configure Apache web server to use generated SSL certificates.

First of all make sure you have installed mod_ssl in your AWS instance. Use following command to install mod_ssl,

sudo yum install mod24_ssl

Then add following lines in your Apache configuration file(httpd.conf) to enable SSL.


     DocumentRoot /var/www/
     ServerName 
     
     SSLEngine on
     SSLCertificateFile /etc/letsencrypt/live//cert.pem
     SSLCertificateKeyFile /etc/letsencrypt/live//privkey.pem
     SSLCertificateChainFile /etc/letsencrypt/live//chain.pem

Restart Apache web server using following command

sudo service httpd restart

Opening 443 port in AWS EC2 instance for HTTPS

Then we have to make sure port 443 of the EC2 instance is opened in your AWS security settings.

Log in to AWS console
Go to Services > EC2
On the left navigation, under Network & Security go to Security Groups.
Select the appropriate security group which governs your EC2 instance.
Select Inbound tab
Add a rule to open 443 port for TCP traffic

Test SSL certificate

Visit https:// to verify the SSL enabled website

Add cron to auto renew Lets Encrypt SSL certificate

You can use Certbot to automatically renew Lets Encrypt SSL certificate. Edit linux crontab and add following line. This would setup a crontab to check and renew SSL certificate if required.

crontab -e

15 0,12 * * * /usr/local/bin/certbot-auto renew >/dev/null 2>&1

My Cute Blog.

Amazon S3 sync script

Admin My Cute Blog — Wed, 16 Aug 2017 17:38:31 +0000

Here is a step by step guide on how to backup your data to amazon S3. At end of this tutorial you will be able to create a bash script to sync your data to amazon S3.

Create a S3 bucket

Log in to your AWS account and go to S3.
Create a new bucket providing a unique name (just use the default settings for now).

Create a user for s3 access

For security purpose let’s create a separate user for S3 access.

Go to aws IAM
Go to users
Click ‘Add user’
Enter a name
Chose only ‘Programmatic access’
Next go to permissions and select ‘Attach existing policies directly’
Grant ‘AmazonS3FullAccess’ policy to user
Download credentials.cvs file on the final step

Amazon CLI configuration

Let’s configure an aws profile to use credentials we have created.
First install AWS CLI according to following guide,
http://docs.aws.amazon.com/cli/latest/userguide/installing.html

Issue following command to verify your AWS CLI setup.

aws --version

If you get the CLI version you are ready to go!

Once you have successfully installed, open a command prompt and issue following command to create a AWS CLI profile.

aws configure --profile my-s3

You can use any name for the profile.

You will be asked for your credentials and region. Provide all your details correctly.

Script to backup files to amazon S3

Use following bash script to backup your data to amazon S3.

#!/bin/bash
aws_profile=my-s3
backup_path=/home/me/backup
bucket_name=my-backup

aws s3 sync $backup_path s3://$bucket_name --storage-class=STANDARD_IA --profile=$aws_profile

You can find more details about these options from: http://docs.aws.amazon.com/cli/latest/reference/s3/sync.html

My Cute Blog.

H2 database example using hibernate and Spring Boot

Sadupa Wijeratne — Sun, 13 Nov 2016 17:09:50 +0000

Here is a H2 database example using Hibernate and Spring Boot. This example shows you how to create, read, update and delete a record in H2 database. I have used maven to build the project.

Download full source code >

H2 example source code (11584 downloads )

If you are new to hibernate you can read my Spring Hibernate tutorial.

Introduction to H2 Database

H2 is an open source embedded database built on java ships in a single .jar file. Therefore you can easily embed h2 database into your application. H2 Database has a built in web based console that you can use to interact with the database. You can use H2 database as a in-memory database, embedded database or network database.

You can find more details about H2 Database from H2 Database official website

H2 Database example application

This example application saves request time in a H2 database for each GET request.

.pom file

First of all here are the maven dependencies for spring boot to use H2 Database and Hibernate



    4.0.0

    com.mycuteblog
    spring-boot-example
    1.0-SNAPSHOT

    
        org.springframework.boot
        spring-boot-starter-parent
        1.3.6.RELEASE
    

    
        
            org.springframework.boot
            spring-boot-starter-web
        

        
            org.springframework.boot
            spring-boot-starter-data-jpa
        

        
            com.h2database
            h2
            ${h2.version}
        
    

    
    
        
            
                org.springframework.boot
                spring-boot-maven-plugin

Model Class

ApiRequest.java class to store api request data.

@Entity
@Table(name = "api_request")
public class ApiRequest {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    @Column(name="request_time")
    private Date requestTime;

    public ApiRequest() {
    }

    public ApiRequest(Date requestTime) {
        this.requestTime = requestTime;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Date getRequestTime() {
        return requestTime;
    }

    public void setRequestTime(Date requestTime) {
        this.requestTime = requestTime;
    }
}

DAO class

ApiRequestDao.java class contains methods for CRUD operations with H2 Database

@Repository
public class ApiRequestDao {
 @PersistenceContext
 private EntityManager entityManager;

 
 public void create(ApiRequest apiRequest) {
 entityManager.persist(apiRequest);
 }

 
 public void update(ApiRequest apiRequest) {
 entityManager.merge(apiRequest);
 }

 
 public ApiRequest getApiRequestById(long id) {
 return entityManager.find(ApiRequest.class, id);
 }

 
 public void delete(long id) {
 ApiRequest apiRequest = getApiRequestById(id);
 if (apiRequest != null) {
 entityManager.remove(apiRequest);
 }
 }

Service class

ApiRequestService.java acts between DAO and our controller

@Transactional
public class ApiRequestService {

@Autowired
 private ApiRequestDao apiRequestDao;

 public void create(ApiRequest apiRequest) {
 apiRequestDao.create(apiRequest);
 }
}

Controller class

ApiRequestController.java is the spring web controller which receives the http GET request an process.

@RestController
@EnableAutoConfiguration
public class ApiRequestController {

    @Autowired
    private ApiRequestService apiRequestService;

    private static final Logger logger = LoggerFactory.getLogger(ApiRequestController.class);

    @RequestMapping(value = "/", produces = MediaType.APPLICATION_JSON_VALUE)
    public Map&lt;String, String&gt; getHome() {
        logger.info("Api request received");

        Map&lt;String, String&gt; response = new HashMap&lt;String, String&gt;();
        try {
            ApiRequest apiRequest = new ApiRequest(new Date());
            apiRequestService.create(apiRequest);
            response.put("status", "success");
        } catch (Exception e) {
            logger.error("Error occurred while trying to process api request", e);
            response.put("status", "fail");
        }

        return response;
    }
}

Main method

We use main method in WebApplication.java to run the application

@SpringBootApplication
public class WebApplication {

    public static void main(String[] args) {
        SpringApplication.run(WebApplication.class, args);
    }
}

Property file

application.properties file contains all the required configurations to connect h2 database and run Spring Boot

server.port = 8080
java.version=1.7

#spring.datasource.url = jdbc:h2:mem:app_db;DB_CLOSE_ON_EXIT=FALSE
spring.datasource.url = jdbc:h2:file:~/h2/app_db;DB_CLOSE_ON_EXIT=FALSE
spring.datasource.username = sa
spring.datasource.password =
spring.datasource.driverClassName = org.h2.Driver
spring.jpa.hibernate.ddl-auto = update

H2 Database console

This is an optional step. Add this class if you wish to enable the h2 database console within your app. Once you add this, H2 database console will be available at http://localhost:8080/console.

@Configuration
public class WebConfiguration {
    @Bean
    ServletRegistrationBean h2servletRegistration(){
        ServletRegistrationBean registrationBean = new ServletRegistrationBean( new WebServlet());
        registrationBean.addUrlMappings("/console/*");
        return registrationBean;
    }
}

That’s all. Build the project and run using mvn spring-boot:run command. Visit following url from your browser to record a api call.
http://localhost:8080

Download full source code >

H2 example source code (11584 downloads )

My Cute Blog.

Spring task scheduler (cron job) example

Sadupa Wijeratne — Mon, 09 Feb 2015 18:33:47 +0000

Spring framework has built in support for scheduled tasks. Here are some examples of spring cron jobs using both annotations and xml configurations.

Download full example >

spring cron example (10127 downloads )

@Scheduled Annotation

You can use @Scheduled annotation to schedule a task very easily. Below are four simple examples to show how to run cron jobs using spring annotations.

Annotation.java

package com.mycuteblog.spring.schedule;

import org.springframework.scheduling.annotation.EnableScheduling;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Service;

import java.util.Date;

@Service
@EnableScheduling
public class Annotation {
 @Scheduled(fixedDelay = 5000)
 public void fixedDelayTask() {
 System.out.println(new Date() + " This runs in a fixed delay");
 }

 @Scheduled(fixedRate = 6000)
 public void fixedRateTask() {
 System.out.println(new Date() + " This runs in a fixed rate");
 }

 @Scheduled(fixedRate = 7000, initialDelay = 2000)
 public void fixedRateWithInitialDelayTask(){
 System.out.println(new Date() + " This runs in a fixed delay with a initial delay");
 }

 @Scheduled(cron = "10 * * * * *")
 public void cronTask(){
 System.out.println(new Date() + " This runs in a cron schedule");
 }
}

fixedDelay: Run tasks with a fixed delay(in example it’s 5 seconds) between last task end time and next task start time. For example, if task starts at 11:00:00 and it takes 3 seconds to execute next task starts at 11:00:08.

fixedRate: Run tasks with a fixed rate of given time. For example in above example
fixedRateTask() is called every 6 seconds. (ie: 11:00:00, 11:00:06, 11:00:12, …)

initialDelay: This can be used with above examples. This property sets delay for first time run. For example, if program starts at 11:00:00 fixedRateWithInitialDelayTask() will run at 11:00:02, 11:00:09, 11:00:16, …

cron: This can be any cron expression.

output

xml Configuration

A cron job can be set using xml configurations too. Following example shows how you can set above cron jobs using xml.

Xml.java

package com.mycuteblog.spring.schedule;

import java.util.Date;

public class Xml {
public void xmlFixedDelayTask() {
System.out.println(new Date() + " This task runs in fixed delay by xml configuration");
}

public void xmlFixedRateTask() {
System.out.println(new Date() + " This task runs in fixed rate by xml configuration");
}

public void xmlCronTask() {
System.out.println(new Date() + " This task runs in a cron schedule by xml configuration");
}
}

spring.xml

I have used maven to build the project. Here is the pom.xml configuration.



 4.0.0

 com.mycuteblog
 spring-schedule
 1.0-SNAPSHOT

 
 
 org.springframework
 spring-context
 4.0.6.RELEASE

Finally here is the main class to test above examples.

SpringScheduleDemo.java

package com.mycuteblog.spring.schedule;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringScheduleDemo {
 public static void main(String[] args) {
 ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
 }
}

output

Download full example >

spring cron example (10127 downloads )

My Cute Blog.

How to send an email in a bash script

Sadupa Wijeratne — Sat, 15 Nov 2014 16:48:46 +0000

You can send an email in a bash script using mutt command. Here I have explained how you can send an email with an attachment to multiple recipients using a linux shell script.

Here is the format of the script.

echo "" | mutt -s "" -a "" -e "my_hdr From:" --

Below is a sample bash script using the above code format.

subject="Email from bash"
body="This email was sent using a bash script"
from="me@example.com"
to="you@example.com other@example.com"
fileAttachment="/tmp/test.txt"

echo "Sending email..."
echo "$body" | mutt -s "$subject" -a "$fileAttachment" -e "my_hdr From:$from" -- $to
echo "Email sent to: $to"

Additionally you can use following parameters,

-c carbon copy (Cc)
-b blind carbon copy (Bcc)

You can view the full parameter list in official mutt website.

My Cute Blog.

Hibernate4 + spring4 + maven example

Sadupa Wijeratne — Tue, 19 Aug 2014 17:15:36 +0000

Here is an example using hibernate4, spring4 and maven. I have described how you can do simple create, read, update and delete operations using hibernate. I have used hibernate annotations for this example.

Download source code ->

Hibernate4 example source code (7752 downloads )

directory structure

Maven Configuration



    4.0.0

    com.mycuteblog
    hibernate4
    1.0-SNAPSHOT

    
        4.0.6.RELEASE
        4.3.6.Final
        5.1.6
    

    
        
        
            org.springframework
            spring-core
            ${spring.version}
        
        
            org.springframework
            spring-context
            ${spring.version}
        
        
            org.springframework
            spring-orm
            ${spring.version}
        

        
        
            org.hibernate
            hibernate-core
            ${hibernate.version}
        
        
            org.hibernate
            hibernate-c3p0
            ${hibernate.version}
        

        
        
            mysql
            mysql-connector-java
            ${mysql.version}

User Class

This class contains all required fields for the users table. Hibernate will create users table automatically using these fields.

@Entity
@Table(name = "users")
public class User {
    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    @Column(name = "user_id")
    private long userId;
    @Column(name = "first_name")
    private String firstName;
    @Column(name = "last_name")
    private String lastName;
    @Column(name = "age")
    private int age;
    @Column(name = "created_date")
    private Date createdDate;

   <-- getters and setters -->
}

Hibernate session factory class

This class is used to get current session from the session factory. Session factory is injected through spring.

public class HibernateSessionFactoryImpl implements HibernateSessionFactory {

    private SessionFactory sessionFactory;

    @Override
    public Session getSession() {
        return this.sessionFactory.getCurrentSession();
    }

    public void setSessionFactory(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
    }
}

User dao

This class contains all CRUD operations for user class.

@Repository
public class UserDaoImpl implements UserDao {

    @Autowired
    HibernateSessionFactory hibernateSessionFactory;

    @Override
    public boolean addUser(User user) {
        Session session = hibernateSessionFactory.getSession();
        session.save(user);
        return true;
    }

    @Override
    public User getUser(long userId) {
        Session session = hibernateSessionFactory.getSession();
        User user = (User) session.createCriteria(User.class)
                .add(Restrictions.eq("userId", userId))
                .uniqueResult();

        return user;
    }

    @Override
    public boolean updateUser(User user) {
        Session session = hibernateSessionFactory.getSession();
        session.update(user);
        return true;
    }

    @Override
    public boolean deleteUser(User user) {
        Session session = hibernateSessionFactory.getSession();
        session.delete(user);
        return true;
    }
}

User Controller

This class handles data using dao class. You can implement your business logic here.

@Transactional
public class UserControllerImpl implements UserController {

    @Autowired
    private UserDao userDao;

    @Override
    public boolean addUser(User user) {
        return userDao.addUser(user);
    }

    @Override
    public User getUser(long userId) {
        return userDao.getUser(userId);
    }

    @Override
    public boolean updateUser(User user) {
        return userDao.updateUser(user);
    }

    @Override
    public boolean deleteUser(User user) {
        return userDao.deleteUser(user);
    }
}

Hibernate configuration

This file contains all required hibernate configurations. I have used cp30 for data pooling.



    
        
        
        
        

        
        
        
        
        
    

    
    
        
            
        

        
            
                org.hibernate.dialect.MySQLDialect
                update

Spring configuration

Here is the main class which tests all we created above.

public class HibernateDemo {

    public static void main(String[] args){

        ApplicationContext context = new ClassPathXmlApplicationContext("spring-beans.xml");

        UserController userController = (UserController) context.getBean("userController");

        User user = new User();
        user.setUserId(100);
        user.setFirstName("Foo");
        user.setLastName("Boo");
        user.setAge(25);
        user.setCreatedDate(new Date());

        userController.addUser(user);

        User savedUser = userController.getUser(100);
        System.out.println(savedUser.toString());

        user.setFirstName("Boo");
        user.setLastName("Foo");
        user.setAge(24);
        userController.updateUser(user);

        User updatedUser = userController.getUser(100);
        System.out.println(updatedUser.toString());

        userController.deleteUser(updatedUser);

        User deletedUser = userController.getUser(100);

        if (deletedUser == null){
            System.out.println("user has been deleted from db");
        }

    }
}

Here is the output

User{id=1, userId=100, firstName='Foo', lastName='Boo', age=25, createdDate=2014-08-19 22:26:55.0}
User{id=1, userId=100, firstName='Boo', lastName='Foo', age=24, createdDate=2014-08-19 22:26:55.0}
user has been deleted from db

Download source code ->

Hibernate4 example source code (7752 downloads )

My Cute Blog.

log4j2 xml configuration example

Sadupa Wijeratne — Sat, 26 Jul 2014 05:19:00 +0000

Here are some sample log4j2 xml configurations.

These configurations should be included in a file named log4j2.xml and placed on the classpath.

Download source code >

log4j2 xml configuration source code (12025 downloads )

Console Appender

Console appender prints all logs to console. Here is a sample output using above configuration.

[INFO ] 2014-07-23 22:04:31.447 [main] LogDemo - Hello world - info log

Daily Rolling File Appender

Daily rolling file appender prints logs to a file. Difference between file appender and daily rolling file appender is, daily rolling file appender creates a log file per day.

This configuration is widely used in commercial systems due to following benefits,

Size of a single log file is smaller
Log analysis is easy
Old log files can be archived or deleted

Here is a sample log4j2 configuration for a daily rolling appender.




logs





[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n

Separate log for error logs

Using following configuration you can have a separate log file for error logs.




logs





[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n

log4j2 full example

Here is a sample java code with all above configurations. I have used maven for dependency management.

LogDemo.java

package com.mycuteblog.log4j2;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

/**
* Created by sadupa on 7/26/14.
*/
public class LogDemo {

private static final Logger logger = LogManager.getLogger(LogDemo.class.getName());

public static void main(String[] args){

logger.debug("Hello world - debug log");
logger.info("Hello world - info log");
logger.warn("Hello world - warn log");
logger.error("Hello world - error log");
}
}

log4j2.xml



    
        logs
    
    
        
            
        
        
            
                [%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n
            
            
                
            
        
        
            
                [%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n

pom.xml



    4.0.0

    com.mycuteblog
    log4j2Demo
    1.0-SNAPSHOT
    jar

    
        
            org.apache.logging.log4j
            log4j-api
            2.0
        
        
            org.apache.logging.log4j
            log4j-core
            2.0
        
    

    
        
            
            org.apache.maven.plugins
            maven-jar-plugin
            2.4
            
                
                    
                        true
                        com.mycuteblog.log4j2.LogDemo
                        dependency-jars/
                    
                
            
        
        
            org.apache.maven.plugins
            maven-dependency-plugin
            2.5.1
            
                
                    copy-dependencies
                    package
                    
                        copy-dependencies
                    
                    
                        
                            ${project.build.directory}/dependency-jars/

Download source code >

log4j2 xml configuration source code (12025 downloads )

Here is the output of above code.

 [DEBUG] 2014-07-26 10:12:50.139 [main] LogDemo - Hello world - debug log
 [INFO ] 2014-07-26 10:12:50.142 [main] LogDemo - Hello world - info log
 [WARN ] 2014-07-26 10:12:50.142 [main] LogDemo - Hello world - warn log
 [ERROR] 2014-07-26 10:12:50.142 [main] LogDemo - Hello world - error log

My Cute Blog.

Run multiple mysql servers on single machine

Sadupa Wijeratne — Wed, 02 Jul 2014 16:57:20 +0000

Here is how to run multiple mysql instances on the same machine. This will be helpful when you need to run different mysql version on same computer or have separate mysql servers for each system.

Here I assume you have already installed one instance of mysql. Following steps are for installing another instance of mysql on a linux system.

Download the required mysql version from dev.mysql.com

Create a separate directory for new mysql instance

We will install new mysql instance on a separate directory. Therefore we can make sure current mysql installation is not affected. This directory will hold mysql databases and other files related to this installation.

sudo mkdir /var/lib/mysql2
cd /var/lib/
chown user.user mysql2

replace user with your current user name.

my.conf Configurations

We have to use some custom configurations for new mysql instance. First copy the existing my.conf file to newly created directory (how to find existing my.cnf file?). Update following settings in the newly copied my.cnf file,

port
pid
socket
datadir

Here is a sample configuration,

port=3307
datadir=/var/lib/mysql2/
socket=/var/lib/mysql2/mysql.sock
pid=/var/lib/mysql2/mysql.pid

Make sure to use a separate port number which will not conflict with current system.

Initializing mysql

Once you have done the configurations you have to run the install script to setup required initial data for mysql.

Go to the downloaded mysql directory and execute following command,

scripts/mysql_install_db --user=mysql --datadir=/var/lib/mysql2/

Make sure you don’t run above code with root permissions. That will avoid any permission issue in the future.

If you run the script successfully you will see mysql data files created in /var/lib/mysql2 directory.

Starting mysql server

Start mysql server using following command

bin/mysqld_safe --user=mysql &

Connecting to mysql server

You can connect to mysql server using following command.

mysql -hlocalhost -P3307 -uroot

Now you can use new mysql server as usual.

My Cute Blog.