To implement your own listener, you just need to write extend some existing listener classes. These classes define hooks that are invoked before or after operations are performed on organization model.

public class MyUserListener extends UserEventListener {

  public void preSave(User user, boolean isNew) throws Exception {
    System.out.println("Before " + (isNew?"creating":"updating") + " user " + user.getUserName());
  }

  public void postSave(User user, boolean isNew) throws Exception { 
    System.out.println("After user " + user.getUserName() + (isNew?" created":" updated"));
  }

  public void preDelete(User user) throws Exception {
    System.out.println("Before deleting user " + user.getUserName());
  }

  public void preDelete(User user) throws Exception {
    System.out.println("After deleting user " + user.getUserName());
  }

}

public class MyGroupListener extends GroupEventListener {

  public void preSave(Group group, boolean isNew) throws Exception {
    System.out.println("Before " + (isNew?"creating":"updating") + " group " + group.getName());
  }

  public void postSave(Group group, boolean isNew) throws Exception { 
    System.out.println("After group " + group.getName() + (isNew?" created":" updated"));
  }

  public void preDelete(Group group) throws Exception {
    System.out.println("Before deleting group " + group.getName());
  }

  public void preDelete(Group group) throws Exception {
    System.out.println("After deleting group " + group.getName());
  }
}

public class MyMembershipListener extends MembershipEventListener {

  public void preSave(Membership membership, boolean isNew) throws Exception {
    System.out.println("Before " + (isNew?"creating":"updating") + " membership.");
  }

  public void postSave(Membership membership, boolean isNew) throws Exception { 
    System.out.println("After membership " + (isNew?" created":" updated"));
  }

  public void preDelete(Membership membership) throws Exception {
    System.out.println("Before deleting membership");
  }

  public void preDelete(Membership membership) throws Exception {
    System.out.println("After deleting membership");
  }
}

Registering the listeners is then achieved by using the ExoContainer plugin mechanism. Learn more about it on the Service Configuration for Beginners article.

To effectively register organization service's listeners you simply need to use the addListenerPlugin seer injector.

So, the easiest way to register your listeners is to pack them into a .jar and create a configuration file into it under mylisteners.jar!/conf/portal/configuration.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<configuration>
 <external-component-plugins>
  <target-component>org.exoplatform.services.organization.OrganizationService</target-component>
   <component-plugin>
    <name>myuserplugin</name>
    <set-method>addListenerPlugin</set-method>
    <type>org.example.MyUserListener</type>
    <description></description>      
   </component-plugin>
   <component-plugin>
    <name>mygroupplugin</name>
    <set-method>addListenerPlugin</set-method>
    <type>org.example.MyGroupListener</type>
    <description></description>      
   </component-plugin>
   <component-plugin>
    <name>mymembershipplugin</name>
    <set-method>addListenerPlugin</set-method>
    <type>org.example.MyMembershipListener</type>
    <description></description>      
   </component-plugin>
  </external-component-plugins>
<configuration>

Now, simply deploy the jar under $TOMCAT_HOME/lib and your listeners are ready!

permission java.lang.RuntimePermission "manageListeners"