Creation timestamp and last update timestamp with Hibernate and MySQL

Question

For a certain Hibernate entity we have a requirement to store its creation time and the last time it was updated. How would you design this?

• What data types would you use in the database (assuming MySQL, possibly in a different timezone that the JVM)? Will the data types be timezone-aware?

• What data types would you use in Java (Date, Calendar, long, ...)?

• Whom would you make responsible for setting the timestamps—the database, the ORM framework (Hibernate), or the application programmer?

• What annotations would you use for the mapping (e.g. @Temporal)?

I'm not only looking for a working solution, but for a safe and well-designed solution.

Answer 1

If you are using the JPA annotations, you can use @PrePersist and @PreUpdate event hooks do this:

@Entity
@Table(name = "entities")    
public class Entity {
  ...

  private Date created;
  private Date updated;

  @PrePersist
  protected void onCreate() {
    created = new Date();
  }

  @PreUpdate
  protected void onUpdate() {
    updated = new Date();
  }
}

or you can use the @EntityListener annotation on the class and place the event code in an external class.