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In this post, we are going to learn how to create custom generator class in hibernate.
Hibernate supports many built in generator classes like
assigned, sequence, increment, identity, native etc. But some requirements these generator classes we can't use. For example while creating new Employee record, i want to insert employee id is
Emp1, Emp2, etc like that. There is no built in generator classes support this type of primary key generated value. So we need to go for Custom generator classes.
In order to create our own generator class, we need to implement with the org.hibernate.id.IdentifierGenerator interface. This interface is having one method. So this method we need override.
We have already seen the different identifier generators supported by Hibernate. However this does not constrain us to use these generators only. Hibernate very magnanimously allows us to create our own custom generator.
This could have been useful to us in one of the modules in our application. We had an entity wherein the Id was an auto-increment field. However later down the project we were given a requirement that in a certain scenario the id needed to be inserted through code and the auto-increment value was not to be used.
Needless to say we came up with a very complex solution and in hindsight today, I can say that it would have been a lot more simpler (and cleaner) to just implement our own custom id generator.
Here is the example code to test Custom generator functionality :
This is hibernate.cfg.xml file for connecting the postgreSQL database.
<?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">oracle.jdbc.driver.OracleDriver</property>
hibernate word is optional <property name="connection.url">jdbc:oracle:thin:@localhost:1521:ORCL</property>
<property name="hibernate.connection.username">kcv</property> <property name="hibernate.connection.password">kcv</property>
<property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>
<property name="show_sql">true</property> <mapping resource="Employee.hbm.xml"/>
</session-factory> -->
<session-factory>
<property name="hibernate.current_session_context_class">thread</property>
<property name="hbm2ddl.auto">create</property>
<property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>
<property name="connection.url">jdbc:postgresql://localhost:5432/hibernate</property>
<property name="connection.username">postgres</property>
<property name="connection.password">password</property>
<property name="connection.driver_class">org.postgresql.Driver</property>
<property name="show_sql">true</property>
<property name="format_sql">true</property>
<property name="use_sql_comments">true</property>
<mapping resource="EmployeeBean.hbm.xml" />
</session-factory>
</hibernate-configuration>
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This is EmployeeBean.hbm.xml mapping file for map the Entity(POJO) class to columns.
<?xml version="1.0" encoding="utf-8"?>
<!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.cv.hibernate.algorithm.model.EmployeeBean"
table="EMPLOYEE_CustomGenerator">
<id name="id" type="java.lang.Long">
<column name="EID" precision="10" scale="0" />
<generator class="com.cv.hibernate.algorithm.CustomGenerator">
</generator>
</id>
<property name="firstName" type="java.lang.String">
<column name="FIRSTNAME" length="29" not-null="true" />
</property>
<property name="lastName" type="java.lang.String">
<column name="LASTNAME" length="29" not-null="true" />
</property>
<property name="email" type="java.lang.String">
<column name="EMAIL" length="39" not-null="true" />
</property>
</class>
</hibernate-mapping>
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This is CustGenTest.java main class having the application business logic.
package com.cv.hibernate.algorithm;
import org.apache.log4j.Logger;
import org.hibernate.Session;
import com.cv.hibernate.algorithm.model.EmployeeBean;
import com.cv.hibernate.algorithm.util.HibernateUtil;
/**
* @author Chandra Vardhan
*/
public class CustGenTest {
/**
* @param args
*/
private final static Logger logger = Logger.getLogger(CustGenTest.class);
public static void main(String[] args) {
Session ses = HibernateUtil.getSession();
EmployeeBean eb = new EmployeeBean();
eb.setFirstName("chandra");
eb.setLastName("vardhan");
eb.setEmail("meetkodam@gmail.com");
ses.beginTransaction();
Long io = (Long) ses.save(eb);
logger.info("Saved successful and Id is : "+io);
ses.getTransaction().commit();
HibernateUtil.closeSession();
}
} |
This is CustomGenerator.java main class having the application business logic.
package com.cv.hibernate.algorithm;
import java.io.Serializable;
import java.util.Random;
import org.hibernate.HibernateException;
import org.hibernate.id.IdentifierGenerator;
/** @author Chandra Vardhan */
public class CustomGenerator implements IdentifierGenerator {
public Serializable generate(
org.hibernate.engine.spi.SessionImplementor arg0, Object arg1)
throws HibernateException {
Random random = new Random();
int value = random.nextInt(100000);
Long value2 = Long.valueOf(value);
return value2;
}
} |
This is EmployeeBean.java Entity(POJO) class having the fields needs to be configured in mapping file.
package com.cv.hibernate.algorithm.model;
/**
* @author Chandra Vardhan
*/
public class EmployeeBean {
private Long id;
private String firstName;
private String lastName;
private String email;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
} |
This is HibernateUtil.java utility class for getting the database connection.
package com.cv.hibernate.algorithm.util;
import org.apache.log4j.Logger;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import com.cv.hibernate.algorithm.model.EmployeeBean;
/**
* Configures and provides access to Hibernate sessions, tied to the current
* thread of execution. Follows the Thread Local Session pattern, see
* {@link http://hibernate.org/42.html }.
*/
public class HibernateUtil {
private final static Logger logger = Logger.getLogger(HibernateUtil.class);
/**
* Location of hibernate.cfg.xml file. Location should be on the classpath
* as Hibernate uses #resourceAsStream style lookup for its configuration
* file. The default classpath location of the hibernate config file is in
* the default package. Use #setConfigFile() to update the location of the
* configuration file for the current session.
*/
private static String CONFIG_FILE_LOCATION = "hibernate.cfg.xml";
private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
private static Configuration configuration = new Configuration();
private static SessionFactory sessionFactory;
static {
try {
configuration = configuration.configure(CONFIG_FILE_LOCATION);
StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder()
.applySettings(configuration.getProperties());
sessionFactory = configuration.buildSessionFactory(builder.build());
logger.info("%%%% Connection successful %%%%");
} catch (Exception e) {
logger.error("%%%% Error Creating SessionFactory %%%%");
e.printStackTrace();
}
}
private HibernateUtil() {
}
/**
* Returns the ThreadLocal Session instance. Lazy initialize the
* <code>SessionFactory</code> if needed.
*
* @return Session
* @throws HibernateException
*/
public static Session getSession() throws HibernateException {
Session session = (Session) threadLocal.get();
if (session == null || !session.isOpen()) {
if (sessionFactory == null) {
rebuildSessionFactory();
}
session = (sessionFactory != null) ? sessionFactory.openSession() : null;
threadLocal.set(session);
}
return session;
}
/**
* Rebuild hibernate session factory
*
*/
public static void rebuildSessionFactory() {
try {
configuration = configuration.configure(CONFIG_FILE_LOCATION);
StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder()
.applySettings(configuration.getProperties());
sessionFactory = configuration.buildSessionFactory(builder.build());
logger.info("%%%% Connection successful %%%%");
} catch (Exception e) {
logger.error("%%%% Error Creating SessionFactory %%%%");
e.printStackTrace();
}
}
/**
* Close the single hibernate session instance.
*
* @throws HibernateException
*/
public static void closeSession() throws HibernateException {
Session session = (Session) threadLocal.get();
threadLocal.set(null);
if (session != null) {
session.close();
System.exit(0);
}
}
/**
* return session factory
*
*/
public static SessionFactory getSessionFactory() {
return sessionFactory;
}
/**
* return hibernate configuration
*
*/
public static Configuration getConfiguration() {
return configuration;
}
public static void saveOrUpdate() {
Session ses = getSession();
EmployeeBean eb = new EmployeeBean();
eb.setId(new Long(101));
eb.setFirstName("chandra");
eb.setLastName("vardhan");
eb.setEmail("meetkodam@gmail.com");
ses.beginTransaction();
ses.saveOrUpdate(eb);
logger.info("Saved successful...");
ses.getTransaction().commit();
ses.close();
}
} |
This is log4j.properties file having the entries for logging the information into the console/file.
#By default enabling Console appender
# Root logger option
log4j.rootLogger=INFO, stdout
# Redirect log messages to console
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%-5p [%c]:%L -->> %m%n
# Redirect log messages to a log file
#log4j.appender.file=org.apache.log4j.RollingFileAppender
#log4j.appender.file.File=C:\\servlet-application.log
#log4j.appender.file.MaxFileSize=5MB
#log4j.appender.file.MaxBackupIndex=10
#log4j.appender.file.layout=org.apache.log4j.PatternLayout
#log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n
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This is pom.xml file having the entries of dependency jars and information to build the application .
| <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.cv.hibernate.algorithm</groupId>
<artifactId>algorithms</artifactId>
<version>1.0</version>
<dependencies>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-entitymanager</artifactId>
<version>4.3.5.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-c3p0</artifactId>
<version>4.3.5.Final</version>
</dependency>
<dependency>
<artifactId>hibernate-core</artifactId>
<groupId>org.hibernate</groupId>
<version>4.3.5.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-validator</artifactId>
<version>4.2.0.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate.common</groupId>
<artifactId>hibernate-commons-annotations</artifactId>
<version>4.0.4.Final</version>
</dependency>
<dependency>
<groupId>org.hibernate.javax.persistence</groupId>
<artifactId>hibernate-jpa-2.0-api</artifactId>
<version>1.0.1.Final</version>
</dependency>
<dependency>
<groupId>javax.validation</groupId>
<artifactId>validation-api</artifactId>
<version>1.0.0.GA</version>
provided
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.6.4</version>
</dependency>
<dependency>
<groupId>org.jboss.logging</groupId>
<artifactId>jboss-logging</artifactId>
<version>3.1.0.CR2</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.6.4</version>
</dependency>
<dependency>
<groupId>postgresql</groupId>
<artifactId>postgresql</artifactId>
<version>9.1-901.jdbc4</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.5</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
</project> |
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