code: public synchronized void addServletReferenceListener(ServletReferenceListener listener) {
          if (this.cacheWrappers == null) {
              cacheWrappers = new ArrayList();
          }
          this.cacheWrappers.add(listener);
      }
docs: /*
  (non-Javadoc)
  
  @seecom.ibm.ws.webcontainer.util.CacheTarget#addCacheWrapper(com.ibm.ws.
  webcontainer.util.CacheWrapper)