Since wiki-page on Liferay.com has out of dated information (not actual for Liferay 6) want to write small reminder how to define model listener in Liferay 6.

What is Model Listener

Model Listener - is a special call-back class, what called then some operation happens with some model - core portal model or any model defined in the portlets.

ModelListener interface looks like

public interface ModelListener<T> {
 public void onAfterAddAssociation(Object classPK, String associationClassName, Object associationClassPK) throws ModelListenerException;

public void onAfterCreate(T model) throws ModelListenerException;

public void onAfterRemove(T model) throws ModelListenerException;

public void onAfterRemoveAssociation(Object classPK, String associationClassName,  Object associationClassPK) throws ModelListenerException;

public void onAfterUpdate(T model) throws ModelListenerException;

public void onBeforeAddAssociation(Object classPK, String associationClassName, Object associationClassPK) throws ModelListenerException;

public void onBeforeCreate(T model) throws ModelListenerException;

public void onBeforeRemove(T model) throws ModelListenerException;

public void onBeforeRemoveAssociation(Object classPK, String associationClassName, Object associationClassPK) throws ModelListenerException;

public void onBeforeUpdate(T model) throws ModelListenerException;
}

It is very close to Hibernate Listener (I think it is based on it) and allow to write reaction on any action with the object. I hope names of methods are clear.

How to implement Model Listener

To implement own listener on some Model (for example User) yin your portlet you need:

1. define property hook in your portlet. In file WEB-INF/liferay-hook.xml you need to have something like:

<hook>

 <portal-properties>portal.properties</portal-properties>

</hook>

2. In file WEB-INF/src/portal.properties define hook for specific model:

value.object.listener.com.liferay.portal.model.User=my.hook.UserListener

3. Implement class by inheriting it from BaseModelListener<T> (in our case BaseModelListener<User>) and implementing only method we want to call-back:

public class GroupListener extends BaseModelListener<Group> {
 @Override
 public void onAfterCreate(Group group) throws ModelListenerException {
   // do something here
 }
}