title: log4j, nested diagnostic contexts
body: <p>I have a MySession object (a generic Session, not web) that runs in its thread. I want to use NDC class in order to include some data taken from fields of my MySession: user that has created it, starting time etc. etc. I'd like to "render" fields into a message. Is it possible or is it supported only for messages?
  Thanks in advance</p>
  
  <pre><code>public class MySession {
      String userName;
      Date startTime;
  
      public void doSomething() {
          NDC.push(this);                                    //cannot do something like this?
          NDC.push(this.userName 
                    + " " + startTime.toString());          //or should I do this? 
      }
  
  }
  </code></pre>