JPA @EntityListeners example

Article.java

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.EntityListeners;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Entity
@EntityListeners({
	CreatedAtListener.class,
	UpdatedAtListener.class
})
@Table(name = "articles")
public class Article implements Creatable, Updatable {
	
	@Id
	@GeneratedValue
	private Integer id;
	
	@Column(nullable = false)
	private String title;
	
	@Column(nullable = false)
	private String author;
	
	@Column(name = "created_at", nullable = false)
	@Temporal(TemporalType.TIMESTAMP)
	private Date createdAt;
	
	@Column(name = "updated_at", nullable = false)
	@Temporal(TemporalType.TIMESTAMP)
	private Date updatedAt;
	
	@Override
	public String toString() {
		return "Article [id=" + id + ", title=" + title + ", author=" + author
			+ ", createdAt=" + createdAt + ", updatedAt=" + updatedAt + "]";
	}
	
	// getters and setters ommited
	
}

Creatable.java

import java.util.Date;

public interface Creatable {
	void setCreatedAt(final Date date);
}

CreatedAtListener.java

import java.util.Date;

import javax.persistence.PrePersist;

public class CreatedAtListener {
	
	@PrePersist
	public void setCreatedAt(final Creatable entity) {
		entity.setCreatedAt(new Date());
	}
	
}

EntityListenersExample.java

public void createAndUpdateArticleExample() {
	
	final Article article = new Article();
	article.setAuthor("Test");
	article.setTitle("title");
	
	System.out.println("Before creation: " + article);
	entityManager.persist(article);
	
	System.out.println("After creation: " + article);
	
	try {
		SECONDS.sleep(2);
	} catch (InterruptedException ex) {
		throw new RuntimeException(ex);
	}
	
	article.setAuthor("Test2");
	entityManager.persist(article);
	entityManager.flush();
	
	System.out.println("After flush: " + article);
}

Output.txt

Before creation: Article [id=null, title=title, author=Test, createdAt=null, updatedAt=null]
After creation: Article [id=1, title=title, author=Test, createdAt=Thu Nov 24 16:36:48 NOVT 2011, updatedAt=Thu Nov 24 16:36:48 NOVT 2011]
After flush: Article [id=1, title=title, author=Test2, createdAt=Thu Nov 24 16:36:48 NOVT 2011, updatedAt=Thu Nov 24 16:36:50 NOVT 2011]

Updatable.java

import java.util.Date;

public interface Updatable {
	void setUpdatedAt(final Date date);
}

UpdatedAtListener.java

import java.util.Date;

import javax.persistence.PrePersist;
import javax.persistence.PreUpdate;

public class UpdatedAtListener {
	
	@PrePersist
	@PreUpdate
	public void setUpdatedAt(final Updatable entity) {
		entity.setUpdatedAt(new Date());
	}
	
}

Nice one! Which package Creatable.java and Updatable.java files goes to?

Entities shouldn't implement interfaces if it can be avoided because it gets you into avoidable trouble with targetEntity.

Nice

I don't know why but it didn't work.

Unfortunately this isn't working for me either, when I try to save my entity, I get:

Caused by: org.hibernate.PropertyValueException: not-null property references a null or transient value : com.business.model.Contactable.modifiedDate
	at org.hibernate.engine.internal.Nullability.checkNullability(Nullability.java:92)
	at org.hibernate.action.internal.AbstractEntityInsertAction.nullifyTransientReferencesIfNotAlready(AbstractEntityInsertAction.java:115)
	at org.hibernate.action.internal.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:69)
	at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:626)
	at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:280)
	at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:261)
	at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:306)
	at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:318)
	at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:275)
	at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:182)
	at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:113)
	at org.hibernate.jpa.event.internal.core.JpaPersistEventListener.saveWithGeneratedId(JpaPersistEventListener.java:67)
	at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:189)
	at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:132)
	at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:58)
	at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:782)
	... 30 more

To make this work, I had to remove nullable = false from the Created Date and Updated Date @column annotations.