Entity Listener: PostLoad : EntityListener « JPA « Java Tutorial

1. Java Tutorial
2. JPA
3. EntityListener

File: EmployeeDebugListener.java

import javax.persistence.PostLoad;
import javax.persistence.PrePersist;
import javax.persistence.PreRemove;
import javax.persistence.PreUpdate;

public class EmployeeDebugListener {

  @PostLoad
  public void postLoad(Employee emp) {
    System.out.println("EmployeeDebugListener.Load called on employee id: " + emp.getId());
  }

}

File: Employee.java

import javax.persistence.Entity;
import javax.persistence.EntityListeners;
import javax.persistence.Id;
import javax.persistence.PostLoad;
import javax.persistence.PostPersist;
import javax.persistence.PostUpdate;
import javax.persistence.PrePersist;
import javax.persistence.PreRemove;
import javax.persistence.PreUpdate;
import javax.persistence.Transient;

@Entity
@EntityListeners({EmployeeDebugListener.class})
public class Employee {
    @Id private int id;
    private String name;
    @Transient private long syncTime;

    @PostPersist 
    @PostUpdate
    @PostLoad 
    private void resetSyncTime() {
        syncTime = System.currentTimeMillis(); 
        System.out.println("Employee.resetSyncTime called on employee id: " + getId());
    }

    public long getCachedAge() {
        return System.currentTimeMillis() - syncTime; 
    }

    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }

    public String toString() {
        return "Employee id: " + getId() ;
    }
}

File: Helper.java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

public class Helper {
  public static void checkData() throws Exception {
    Class.forName("org.hsqldb.jdbcDriver");
    Connection conn = DriverManager.getConnection("jdbc:hsqldb:data/tutorial", "sa", "");
    Statement st = conn.createStatement();

    ResultSet mrs = conn.getMetaData().getTables(null, null, null, new String[] { "TABLE" });
    while (mrs.next()) {
      String tableName = mrs.getString(3);
      System.out.println("\n\n\n\nTable Name: "+ tableName);

      ResultSet rs = st.executeQuery("select * from " + tableName);
      ResultSetMetaData metadata = rs.getMetaData();
      while (rs.next()) {
        System.out.println(" Row:");
        for (int i = 0; i < metadata.getColumnCount(); i++) {
          System.out.println("    Column Name: "+ metadata.getColumnLabel(i + 1)+ ",  ");
          System.out.println("    Column Type: "+ metadata.getColumnTypeName(i + 1)+ ":  ");
          Object value = rs.getObject(i + 1);
          System.out.println("    Column Value: "+value+"\n");
        }
      }
    }
  }
}

File: Main.java

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;

public class Main {
  static EntityManagerFactory emf = Persistence.createEntityManagerFactory("JPAService");

  static EntityManager em = emf.createEntityManager();

  public static void main(String[] a) throws Exception {
    em.getTransaction().begin();

    
    Employee emp = new Employee();
    
    emp.setId(1);
    
    em.persist(emp);


    em.getTransaction().commit();
    em.close();
    emf.close();

    Helper.checkData();
  }
}

File: persistence.xml

<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" version="1.0">
  <persistence-unit name="JPAService" transaction-type="RESOURCE_LOCAL">
    <properties>
      <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
      <property name="hibernate.hbm2ddl.auto" value="update"/>
      <property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/>
      <property name="hibernate.connection.username" value="sa"/>
      <property name="hibernate.connection.password" value=""/>
      <property name="hibernate.connection.url" value="jdbc:hsqldb:data/tutorial"/>
    </properties>
  </persistence-unit>
</persistence>

22.34.EntityListener
	22.34.1.	One Entity With Two Listeners
	22.34.2.	Exclude Super class Listeners In Super Class
	22.34.3.	Entity Listeners PrePersist
	22.34.4.	Entity Listener: PreUpdate
	22.34.5.	Entity Listener: PreRemove
	22.34.6.	Entity Listener: PostLoad
	22.34.7.	Add Entity Listeners To subclasses