/**

  * Copyright 2005-2011 The Kuali Foundation

  *

  * Licensed under the Educational Community License, Version 2.0 (the "License");

  * you may not use this file except in compliance with the License.

  * You may obtain a copy of the License at

  *

  * http://www.opensource.org/licenses/ecl2.php

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package org.kuali.rice.ksb.messaging;

 import org.apache.commons.lang.StringUtils;

 import org.apache.log4j.Logger;

 import org.kuali.rice.core.api.resourceloader.GlobalResourceLoader;

 import javax.xml.namespace.QName;

 import java.lang.reflect.InvocationHandler;

 import java.lang.reflect.Method;

 import java.lang.reflect.Proxy;

 /**

  * This class creates a proxy for services deployed on KSB. A 

  * reference to the service is obtained only upon the first method

  * invocation.

  * 

  * @author Kuali Rice Team (rice.collab@kuali.org)

  *

  */

 public class KSBClientProxy implements InvocationHandler {

 private static final Logger LOG = Logger.getLogger(KSBClientProxy.class);

     private QName serviceName;

     private volatile Object service;

     public static <T> T newInstance(String serviceQName, Class<T> interfaceClass) throws InstantiationException, IllegalAccessException {

         if (StringUtils.isBlank(serviceQName)) {

             throw new IllegalArgumentException("the qname was blank");

         }

         if (interfaceClass == null) {

             throw new IllegalArgumentException("the interfaceClass was null");

         }

         @SuppressWarnings("unchecked")

         final T t = (T)Proxy.newProxyInstance(interfaceClass.getClassLoader(), new Class[] { interfaceClass }, new KSBClientProxy(serviceQName));

         return t;

     }

     public KSBClientProxy(String serviceQName){

         if (StringUtils.isBlank(serviceQName)) {

             throw new IllegalArgumentException("the qname was blank");

         }

         this.serviceName = QName.valueOf(serviceQName);

     }

     public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

         //using DCL idiom

         //see effective java 2nd ed. pg. 71

         Object s = service;

         if (s == null) {

             synchronized (this) {

                 s = service;

                 if (s == null) {

                     service = s = GlobalResourceLoader.getService(serviceName);

                 }

             }

         }

         if (s != null) {

             return method.invoke(s, args);

         }

         LOG.warn("serviceName: " + serviceName + " was not found");

         return null;

     }

 }