/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache 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
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * 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.springframework.ejb.access;

import java.lang.reflect.InvocationTargetException;
import java.rmi.RemoteException;
import javax.ejb.CreateException;
import javax.ejb.EJBObject;
import javax.naming.NamingException;

import org.aopalliance.intercept.MethodInvocation;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.remoting.RemoteLookupFailureException;
import org.springframework.remoting.rmi.RmiClientInterceptorUtils;

/**
 * Basic invoker for a remote Stateless Session Bean.
 * Designed for EJB 2.x, but works for EJB 3 Session Beans as well.
 *
 * <p>"Creates" a new EJB instance for each invocation, or caches the session
 * bean instance for all invocations (see {@link #setCacheSessionBean}).
 * See {@link org.springframework.jndi.JndiObjectLocator} for info on
 * how to specify the JNDI location of the target EJB.
 *
 * <p>In a bean container, this class is normally best used as a singleton. However,
 * if that bean container pre-instantiates singletons (as do the XML ApplicationContext
 * variants) you may have a problem if the bean container is loaded before the EJB
 * container loads the target EJB. That is because by default the JNDI lookup will be
 * performed in the init method of this class and cached, but the EJB will not have been
 * bound at the target location yet. The best solution is to set the "lookupHomeOnStartup"
 * property to "false", in which case the home will be fetched on first access to the EJB.
 * (This flag is only true by default for backwards compatibility reasons).
 *
 * <p>This invoker is typically used with an RMI business interface, which serves
 * as super-interface of the EJB component interface. Alternatively, this invoker
 * can also proxy a remote SLSB with a matching non-RMI business interface, i.e. an
 * interface that mirrors the EJB business methods but does not declare RemoteExceptions.
 * In the latter case, RemoteExceptions thrown by the EJB stub will automatically get
 * converted to Spring's unchecked RemoteAccessException.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 09.05.2003
 * @see org.springframework.remoting.RemoteAccessException
 * @see AbstractSlsbInvokerInterceptor#setLookupHomeOnStartup
 * @see AbstractSlsbInvokerInterceptor#setCacheHome
 * @see AbstractRemoteSlsbInvokerInterceptor#setRefreshHomeOnConnectFailure
 */
public class SimpleRemoteSlsbInvokerInterceptor extends AbstractRemoteSlsbInvokerInterceptor
                implements DisposableBean {

        private boolean cacheSessionBean = false;

        private Object beanInstance;

        private final Object beanInstanceMonitor = new Object();


        /**
         * Set whether to cache the actual session bean object.
         * <p>Off by default for standard EJB compliance. Turn this flag
         * on to optimize session bean access for servers that are
         * known to allow for caching the actual session bean object.
         * @see #setCacheHome
         */
        public void setCacheSessionBean(boolean cacheSessionBean) {
                this.cacheSessionBean = cacheSessionBean;
        }


        /**
         * This implementation "creates" a new EJB instance for each invocation.
         * Can be overridden for custom invocation strategies.
         * <p>Alternatively, override {@link #getSessionBeanInstance} and
         * {@link #releaseSessionBeanInstance} to change EJB instance creation,
         * for example to hold a single shared EJB component instance.
         */
        @Override
        protected Object doInvoke(MethodInvocation invocation) throws Throwable {
                Object ejb = null;
                try {
                        ejb = getSessionBeanInstance();
                        return RmiClientInterceptorUtils.invokeRemoteMethod(invocation, ejb);
                }
                catch (NamingException ex) {
                        throw new RemoteLookupFailureException("Failed to locate remote EJB [" + getJndiName() + "]", ex);
                }
                catch (InvocationTargetException ex) {
                        Throwable targetEx = ex.getTargetException();
                        if (targetEx instanceof RemoteException) {
                                RemoteException rex = (RemoteException) targetEx;
                                throw RmiClientInterceptorUtils.convertRmiAccessException(
                                        invocation.getMethod(), rex, isConnectFailure(rex), getJndiName());
                        }
                        else if (targetEx instanceof CreateException) {
                                throw RmiClientInterceptorUtils.convertRmiAccessException(
                                        invocation.getMethod(), targetEx, "Could not create remote EJB [" + getJndiName() + "]");
                        }
                        throw targetEx;
                }
                finally {
                        if (ejb instanceof EJBObject) {
                                releaseSessionBeanInstance((EJBObject) ejb);
                        }
                }
        }

        /**
         * Return an EJB component instance to delegate the call to.
         * <p>The default implementation delegates to {@link #newSessionBeanInstance}.
         * @return the EJB component instance
         * @throws NamingException if thrown by JNDI
         * @throws InvocationTargetException if thrown by the create method
         * @see #newSessionBeanInstance
         */
        protected Object getSessionBeanInstance() throws NamingException, InvocationTargetException {
                if (this.cacheSessionBean) {
                        synchronized (this.beanInstanceMonitor) {
                                if (this.beanInstance == null) {
                                        this.beanInstance = newSessionBeanInstance();
                                }
                                return this.beanInstance;
                        }
                }
                else {
                        return newSessionBeanInstance();
                }
        }

        /**
         * Release the given EJB instance.
         * <p>The default implementation delegates to {@link #removeSessionBeanInstance}.
         * @param ejb the EJB component instance to release
         * @see #removeSessionBeanInstance
         */
        protected void releaseSessionBeanInstance(EJBObject ejb) {
                if (!this.cacheSessionBean) {
                        removeSessionBeanInstance(ejb);
                }
        }

        /**
         * Reset the cached session bean instance, if necessary.
         */
        @Override
        protected void refreshHome() throws NamingException {
                super.refreshHome();
                if (this.cacheSessionBean) {
                        synchronized (this.beanInstanceMonitor) {
                                this.beanInstance = null;
                        }
                }
        }

        /**
         * Remove the cached session bean instance, if necessary.
         */
        @Override
        public void destroy() {
                if (this.cacheSessionBean) {
                        synchronized (this.beanInstanceMonitor) {
                                if (this.beanInstance instanceof EJBObject) {
                                        removeSessionBeanInstance((EJBObject) this.beanInstance);
                                }
                        }
                }
        }

}