被@Prepersist注解的方法 ，完成save之前的操作。
被@Preupdate注解的方法 ，完成update之前的操作。
被@PreRemove注解的方法 ，完成remove之前的操作。
被@Postpersist注解的方法 ，完成save之后的操作。
被@Postupdate注解的方法 ，完成update之后的操作。
被@PostRemovet注解的方法 ，完成remove之后的操作。

?This page will provide JPA @EntityListeners example with callbacks @PrePersist, @PostPersist, @PostLoad, @PreUpdate, @PostUpdate, @PreRemove, @PostRemove. JPA?@EntityListeners?is used on entity or mapped superclass at class level. JPA provides callback methods for saving, fetching, updating and removing data from database. Here we will use JPA?EntityManager?to interact with database.

JPA @EntityListeners

@EntityListeners?annotation specifies the callback listener classes . This annotation can be used for an entity or mapped superclass.?
1. To configure single callback listener class, we can do as follows.

@EntityListeners(UserListener.class) public class User {}

2. To configure multiple callback listener classes, we can do as follows.

@EntityListeners({UserListener1.class, UserListener2.class}) public class User { }

JPA Callbacks Method

JPA provides callback methods to listen saving, fetching, updating and removing data from database. These callback methods annotated in a listener bean class must have return type?void?and accept?one argument.?

@PrePersist: The method annotated with?@PrePersist?in listener bean class is called before persisting data by entity manager?persist()?method.?

@PostPersist: The method annotated with?@PostPersist?is called after persisting data.?

@PostLoad: The method annotated with?@PostLoad?is called after fetching data using entity manager?find()?method in persistence context or refreshing it with database by using?refresh()?method. If the entity instance is already loaded in persistence context, then calling of?find()?method will not call?@PostLoad.?

@PreUpdate: The method annotated with?@PreUpdate?in listener bean class is called before updating data.?

@PostUpdate: It is called after updating data.?

@PreRemove: The method annotated with?@PreRemove?in listener bean class is called before removing data by using entity manager?remove()?method.?

@PostRemove: It is called after removing data.

Database Schema

For the demo we are using a table with following schema created in MySQL.?
Table: user

CREATE TABLE `user` (`id` INT(11) NOT NULL,`name` VARCHAR(255) NULL DEFAULT NULL,PRIMARY KEY (`id`) ) COLLATE='latin1_swedish_ci' ENGINE=InnoDB;

Gradle File

Find the gradle file.?
build.gradle

apply plugin: 'java' apply plugin: 'eclipse' archivesBaseName = 'HibernateJPA' version = '1' repositories {mavenCentral() } dependencies {compile 'org.hibernate:hibernate-entitymanager:5.0.7.Final'compile 'mysql:mysql-connector-java:5.1.31' }

Create Listener Class

Find the listener class which consist callback methods annotated with @PrePersist, @PostPersist, @PostLoad, @PreUpdate, @PostUpdate, @PreRemove and @PostRemove.?
UserListener.java

package com.concretepage; import javax.persistence.PostLoad; import javax.persistence.PostPersist; import javax.persistence.PostRemove; import javax.persistence.PostUpdate; import javax.persistence.PrePersist; import javax.persistence.PreRemove; import javax.persistence.PreUpdate; public class UserListener {@PrePersistpublic void userPrePersist(User ob) {System.out.println("Listening User Pre Persist : " + ob.getName());}@PostPersistpublic void userPostPersist(User ob) {System.out.println("Listening User Post Persist : " + ob.getName());}@PostLoadpublic void userPostLoad(User ob) {System.out.println("Listening User Post Load : " + ob.getName());} @PreUpdatepublic void userPreUpdate(User ob) {System.out.println("Listening User Pre Update : " + ob.getName());}@PostUpdatepublic void userPostUpdate(User ob) {System.out.println("Listening User Post Update : " + ob.getName());}@PreRemovepublic void userPreRemove(User ob) {System.out.println("Listening User Pre Remove : " + ob.getName());}@PostRemovepublic void userPostRemove(User ob) {System.out.println("Listening User Post Remove : " + ob.getName());} }

Create Entity annotated with @EntityListeners

Now find the entity annotated with?@EntityListeners.?
User.java

package com.concretepage; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.EntityListeners; import javax.persistence.Id; import javax.persistence.Table; @Entity @EntityListeners(UserListener.class) @Table(name="user") public class User {@Id@Column(name="id")private int id;@Column(name="name")private String name;public User() {}public User(int id, String name) {this.id = id;this.name = name;}public int getId() {return id;} public String getName() {return name;}public void setName(String name) {this.name = name;} }

persistence.xml

Find the persistence.xml file.

<?xml version="1.0" encoding="UTF-8" ?> <persistence xmlns="http://java.sun.com/xml/ns/persistence"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"version="2.0"><persistence-unit name="com.concretepage"><description>JPA Demo</description><provider>org.hibernate.ejb.HibernatePersistence</provider><properties><property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/><property name="hibernate.hbm2ddl.auto" value="update"/><property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/><property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost/concretepage"/><property name="javax.persistence.jdbc.user" value="root"/><property name="javax.persistence.jdbc.password" value=""/></properties></persistence-unit> </persistence>

Run Application

First find the JPA utility singleton class that will provide the instance of?EntityManager.?
JPAUtility.java

package com.concretepage; import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; public class JPAUtility {private static final EntityManagerFactory emFactory;static {emFactory = Persistence.createEntityManagerFactory("com.concretepage");}public static EntityManager getEntityManager(){return emFactory.createEntityManager();}public static void close(){emFactory.close();} }

Find the class to test the application.?
JPAListenerDemo.java

package com.concretepage; import javax.persistence.EntityManager; public class JPAListenerDemo {public static void main(String[] args) {EntityManager entityManager = JPAUtility.getEntityManager(); entityManager.getTransaction().begin();//persist userUser user = new User(1, "Mahesh");entityManager.persist(user);entityManager.getTransaction().commit();//refresh userentityManager.refresh(user);//update userentityManager.getTransaction().begin(); user.setName("Krishna");entityManager.getTransaction().commit();//remove userentityManager.getTransaction().begin(); entityManager.remove(user);entityManager.getTransaction().commit(); entityManager.close();JPAUtility.close(); } }

Find the output.

Listening User Pre Persist : Mahesh Listening User Post Persist : Mahesh Listening User Post Load : Mahesh Listening User Pre Update : Krishna Listening User Post Update : Krishna Listening User Pre Remove : Krishna Listening User Post Remove : Krishna

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