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     */
016    package org.kuali.rice.ksb.messaging;
017    
018    import org.apache.commons.lang.StringUtils;
019    import org.apache.commons.lang.exception.ExceptionUtils;
020    import org.apache.log4j.Logger;
021    import org.kuali.rice.core.api.resourceloader.GlobalResourceLoader;
022    
023    import javax.xml.namespace.QName;
024    import java.lang.reflect.InvocationHandler;
025    import java.lang.reflect.InvocationTargetException;
026    import java.lang.reflect.Method;
027    import 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     */
037    public class KSBClientProxy implements InvocationHandler {
038    
039    private 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    }