001/**
002 * Copyright 2005-2012 The Kuali Foundation
003 *
004 * Licensed under the Educational Community License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.opensource.org/licenses/ecl2.php
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016package org.kuali.rice.ksb.messaging;
017
018import org.apache.commons.lang.StringUtils;
019import org.apache.commons.lang.exception.ExceptionUtils;
020import org.apache.log4j.Logger;
021import org.kuali.rice.core.api.resourceloader.GlobalResourceLoader;
022
023import javax.xml.namespace.QName;
024import java.lang.reflect.InvocationHandler;
025import java.lang.reflect.InvocationTargetException;
026import java.lang.reflect.Method;
027import java.lang.reflect.Proxy;
028
029/**
030 * This class creates a proxy for services deployed on KSB. A 
031 * reference to the service is obtained only upon the first method
032 * invocation.
033 * 
034 * @author Kuali Rice Team (rice.collab@kuali.org)
035 *
036 */
037public class KSBClientProxy implements InvocationHandler {
038
039private static final Logger LOG = Logger.getLogger(KSBClientProxy.class);
040    
041    private QName serviceName;
042    private volatile Object service;
043
044
045    public static <T> T newInstance(String serviceQName, Class<T> interfaceClass) throws InstantiationException, IllegalAccessException {
046        if (StringUtils.isBlank(serviceQName)) {
047            throw new IllegalArgumentException("the qname was blank");
048        }
049
050        if (interfaceClass == null) {
051            throw new IllegalArgumentException("the interfaceClass was null");
052        }
053
054        @SuppressWarnings("unchecked")
055        final T t = (T)Proxy.newProxyInstance(interfaceClass.getClassLoader(), new Class[] { interfaceClass }, new KSBClientProxy(serviceQName));
056        return t;
057    }
058
059    public KSBClientProxy(String serviceQName){
060        if (StringUtils.isBlank(serviceQName)) {
061            throw new IllegalArgumentException("the qname was blank");
062        }
063
064        this.serviceName = QName.valueOf(serviceQName);
065    }
066    
067    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
068        //using DCL idiom
069        //see effective java 2nd ed. pg. 71
070        Object s = service;
071        if (s == null) {
072            synchronized (this) {
073                s = service;
074                if (s == null) {
075                    service = s = GlobalResourceLoader.getService(serviceName);
076                }
077            }
078        }
079
080        if (s != null) {
081            try {
082                return method.invoke(s, args);
083            } catch (InvocationTargetException e) {
084                throw ExceptionUtils.getRootCause(e);
085            }
086        }
087
088        LOG.warn("serviceName: " + serviceName + " was not found");
089        return null;
090    }
091}