org.springframework.orm.hibernate4.support.OpenSessionInterceptor

/*
 * Copyright 2002-2014 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
 *
 *      http://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.orm.hibernate4.support;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.hibernate.FlushMode;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.dao.DataAccessResourceFailureException;
import org.springframework.orm.hibernate4.SessionFactoryUtils;
import org.springframework.orm.hibernate4.SessionHolder;
import org.springframework.transaction.support.TransactionSynchronizationManager;

/**
 * Simple AOP Alliance {@link MethodInterceptor} implementation that binds a new
 * Hibernate {@link Session} for each method invocation, if none bound before.
 *简单的aop 绑定，实现绑定一个新的hibernate对象，如果没有绑定,则绑定每一个hibernate方法。
 * <p>This is a simple Hibernate Session scoping interceptor along the lines of
　　这是一个简单的hibernae session 范围之上的拦截器
 * {@link OpenSessionInViewInterceptor}, just for use with AOP setup instead of
　　只是以 AOP 设置代替 MVC 设置。
 * MVC setup. It opens a new {@link Session} with flush mode "MANUAL" since the
　　           它 打开 一个 新的 flush mode="manual" ,因为这个是只读的，                  
 * Session is only meant for reading, except when participating in a transaction.
 *　　　　　　　　　　　　　　　　　　　　　除非加入了事务。
 * @author Juergen Hoeller
 * @since 4.0.2
 * @see OpenSessionInViewInterceptor
 * @see OpenSessionInViewFilter
 * @see org.springframework.orm.hibernate4.HibernateTransactionManager
 * @see org.springframework.transaction.support.TransactionSynchronizationManager
 * @see org.hibernate.SessionFactory#getCurrentSession()
 */
public class OpenSessionInterceptor implements MethodInterceptor, InitializingBean {

    private SessionFactory sessionFactory;


    /**
     * Set the Hibernate SessionFactory that should be used to create Hibernate Sessions.
     */
    public void setSessionFactory(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
    }

    /**
     * Return the Hibernate SessionFactory that should be used to create Hibernate Sessions.
     */
    public SessionFactory getSessionFactory() {
        return this.sessionFactory;
    }

    @Override
    public void afterPropertiesSet() {
        if (getSessionFactory() == null) {
            throw new IllegalArgumentException("Property ‘sessionFactory‘ is required");
        }
    }


    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        SessionFactory sf = getSessionFactory();
　　　　　　//检测当前的SessionFactory是否绑定到当前现场中。
        if (!TransactionSynchronizationManager.hasResource(sf)) {
            // New Session to be bound for the current method‘s scope...
　　　　　　　　//通过后面的openSession,获得当前现场绑定的sessionFactory并打开session，然后将其绑定到当前方法中。（暂时不说太理解这个？）

            Session session = openSession();
            try {
　　　　　　　　//将SessionFactory和session绑定到当前线程。（奇怪，上面的if不是已经检测到sessionFactory绑定到当前的thread了吗，）
                TransactionSynchronizationManager.bindResource(sf, new SessionHolder(session));
                return invocation.proceed();    //继续进行下一个拦截器
            }
            finally {
                SessionFactoryUtils.closeSession(session);
                TransactionSynchronizationManager.unbindResource(sf);   //将sf从当前thread解绑。
            }
        }
        else {
            // Pre-bound Session found -> simply proceed.
            return invocation.proceed();
        }
    }

    /**
     * Open a Session for the SessionFactory that this interceptor uses.
     * <p>The default implementation delegates to the {@link SessionFactory#openSession}
     * method and sets the {@link Session}‘s flush mode to "MANUAL".
     * @return the Session to use
     * @throws DataAccessResourceFailureException if the Session could not be created
     * @see org.hibernate.FlushMode#MANUAL
     */
    protected Session openSession() throws DataAccessResourceFailureException {
        try {
            Session session = getSessionFactory().openSession();
            session.setFlushMode(FlushMode.MANUAL);
            return session;
        }
        catch (HibernateException ex) {
            throw new DataAccessResourceFailureException("Could not open Hibernate Session", ex);
        }
    }

}