Today I run again into my old problem with the PortletStateHolder. While he is under fire he throws a lot of ConcurrentModificationExceptions.

Here is one of these Exceptions:

Caused by: java.util.ConcurrentModificationException
at java.util.LinkedHashMap$LinkedHashIterator.nextEntry(LinkedHashMap.java:373)
at java.util.LinkedHashMap$KeyIterator.next(LinkedHashMap.java:384)
at de.koelnerwasser.portlet.bridge.MyPortletStateHolder
         .removeSessionStates(MyPortletStateHolder.javaa:198)

Because I synchronized every write access to the class variable “states” eg.:

public void addWindowState(StateId stateId, PortletWindowState state) {
  // prevent concurrent access
  synchronized (states) {
    states.put(stateId, state);
  }
 }

I wonder about the exceptions.  So I investigated the read access to “states” in the “getWindowState()” method:

public PortletWindowState getWindowState(StateId stateId) {
 PortletWindowState state = null;
  if (null != stateId) {
   state = states.get(stateId);
  }
  return state;
 }

I found that states.get() calls a put on the org.apache.commons.collections.LRUMap. Here is the code:

public Object get(Object key)
{
  if(!containsKey(key))
  {
    return null;
  } else {
    Object value = remove(key);
    super.put(key, value);
    return value;
  }

The put() call causes the ConcurrentModificationException. The solution is to synchronize every call on the state LRUMap.