How to pass a parameter to a callback method

Question

I have a requirement where I have to store audit information for every insert/update/delete. Info to be stored will be update time and user id .

I learned from this tutorial that I can use entity listeners and callback methods like @PrePersist .

I know how to handle the update time inside the callback methods but I don't know how I can set the userId in entity inside the callback methods:

@PrePersist
private void prePersist() {
   this.updateTime = new Date();
   this.userId = ???;
}

How can I pass the ID of the current user to callback methods?

Answer 1

You can't pass any information to the callback methods with the Hibernate or JPA API directly.

But there is another common solution: ThreadLocal

A ThreadLocal stores a static variable for the current running thread. And as a request is usually executed in exactly one thread, you can access that information from your callback method / listener. Some UI framework create already a ThreadLocal for you.

For example JSF provides one with FacesContext.getCurrentInstance() . So in JSF you could call:

FacesContext.getCurrentInstance().getExternalContext().getRemoteUser()

Or in Spring with the RequestContextHolder :

((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest().getRemoteUser()

If you've got no such framework you can build your own ThreadLocal :

public final class UserIdHelper {
  // You can add the static ThreadLocal to any class, just as an example
  private static final ThreadLocal<String> userIds = new ThreadLocal<>();

  public static void setCurrentUserId(String userId) {
    userIds.set(userId);
  }

  public static String getCurrentUserId() {
    return userIds.get();
  }

  public static void removeCurrentUserId() {
    userIds.remove();
  }
}

Now you can set the userId in a Filter or just around your JPA calls:

UserIdHelper.setCurrentUserId(request.getRemoteUser());
try {
  // ... Execute your JPA calls ...
} finally {
  UserIdHelper.removeCurrentUserId();
}

It is important to remove the userId in the finally block - otherwise a follow up request running in the same thread could "hijack" your previous userId .

To access that information in your callback method:

@PrePersist
private void prePersist() {
  this.createdBy = UserIdHelper.getCurrentUserId();
}