基于JDK动态代理和CGLIB动态代理的实现Spring注解管理事务（@Trasactional）到底有什么区别。

一、基础工作

首先修改我们上一次做的 SpringMVC + spring3.1.1 + hibernate4.1.0 集成及常见问题总结，如下所示：

    将xml声明式事务删除

 

 

java代码：

<aop:config expose-proxy="true">
        <!-- 只对业务逻辑层实施事务 -->
        <aop:pointcut id="txPointcut" expression="execution(* cn.javass..service..*.*(..))" />
        <aop:advisor advice-ref="txAdvice" pointcut-ref="txPointcut"/>
    </aop:config>

<aop:config expose-proxy="true">
        <!-- 只对业务逻辑层实施事务 -->
        <aop:pointcut id="txPointcut" expression="execution(* cn.javass..service..*.*(..))" />
        <aop:advisor advice-ref="txAdvice" pointcut-ref="txPointcut"/>
    </aop:config>

 

    并添加注解式事务支持：

 

 

java代码：

<tx:annotation-driven transaction-manager="txManager"/>

<tx:annotation-driven transaction-manager="txManager"/>

 

    在我们的BaseService接口上添加 @Transactional 使该方法开启事务

 

 

java代码：

package cn.javass.common.service;
public interface IBaseService<M extends java.io.Serializable, PK extends java.io.Serializable> {
@Transactional   //开启默认事务
    public int countAll();
}

package cn.javass.common.service;
public interface IBaseService<M extends java.io.Serializable, PK extends java.io.Serializable> {
@Transactional   //开启默认事务
    public int countAll();
}  

 

在我们的log4j.properties中添加如下配置，表示输出spring的所有debug信息

 

java代码：

log4j.logger.org.springframework=INFO,CONSOLE

log4j.logger.org.springframework=INFO,CONSOLE

 

在我们的resources.properties里将hibernate.show_sql=true 改为true，为了看到hibernate的sql。

 

 

单元测试类：

 

java代码：

package cn.javass.ssonline.spider.service.impl;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.test.context.transaction.TransactionConfiguration;

import cn.javass.demo.service.UserService;
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"classpath:spring-config.xml"})
public class UserServiceTest2 {

    @Autowired
    private UserService userService;
    @Test
    public void testCreate() {
       userService.countAll();
    }
}

package cn.javass.ssonline.spider.service.impl;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.test.context.transaction.TransactionConfiguration;

import cn.javass.demo.service.UserService;
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"classpath:spring-config.xml"})
public class UserServiceTest2 {
    
    @Autowired
    private UserService userService;
    @Test
    public void testCreate() {
       userService.countAll();
    }
}

 

基础工作做好，接下来我们详细看看 Spring基于 JDK动态代理 和 CGLIB类级别代理到底有什么区别。

 

 

二、基于JDK动态代理：

 

java代码：

<tx:annotation-driven transaction-manager="txManager"/>

<tx:annotation-driven transaction-manager="txManager"/>

   该配置方式默认就是JDK动态代理方式

 

运行单元测试，核心日志如下：                                     

 

java代码：

2012-03-07 09:58:44 [main] DEBUG org.springframework.orm.hibernate4.HibernateTransactionManager - Creating new transaction with name [cn.javass.common.service.impl.BaseService.countAll]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT; ''      //开启事务
2012-03-07 09:58:44 [main] DEBUG org.springframework.orm.hibernate4.HibernateTransactionManager - Opened new Session

2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.support.TransactionSynchronizationManager - Bound value [org.springframework.orm.hibernate4.SessionHolder@1184a4f] for key [org.hibernate.internal.SessionFactoryImpl@107b56e] to thread [main] //绑定session到ThreadLocal
2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.support.TransactionSynchronizationManager - Initializing transaction synchronization
2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.interceptor.TransactionInterceptor - Getting transaction for [cn.javass.common.service.impl.BaseService.countAll]
2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.support.TransactionSynchronizationManager - Retrieved value [org.springframework.orm.hibernate4.SessionHolder@1184a4f] for key [org.hibernate.internal.SessionFactoryImpl@107b56e] bound to thread [main]
2012-03-07 09:58:44 [main] DEBUG org.springframework.orm.hibernate4.HibernateTransactionManager - Found thread-bound Session

2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.support.TransactionSynchronizationManager - Retrieved value [org.springframework.orm.hibernate4.SessionHolder@1184a4f] for key [org.hibernate.internal.SessionFactoryImpl@107b56e] bound to thread [main]
Hibernate:
    select
        count(*) as col_0_0_
    from
        tbl_user usermodel0_

2012-03-07 09:58:44 [main] DEBUG org.springframework.orm.hibernate4.HibernateTransactionManager - Committing Hibernate transaction on Session    //提交事务

2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.support.TransactionSynchronizationManager - Removed value [org.springframework.orm.hibernate4.SessionHolder@1184a4f] for key [org.hibernate.internal.SessionFactoryImpl@107b56e] from thread [main] //解除绑定session到ThreadLocal

2012-03-07 09:58:44 [main] DEBUG org.springframework.orm.hibernate4.HibernateTransactionManager - Creating new transaction with name [cn.javass.common.service.impl.BaseService.countAll]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT; ''      //开启事务
2012-03-07 09:58:44 [main] DEBUG org.springframework.orm.hibernate4.HibernateTransactionManager - Opened new Session 

2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.support.TransactionSynchronizationManager - Bound value [org.springframework.orm.hibernate4.SessionHolder@1184a4f] for key [org.hibernate.internal.SessionFactoryImpl@107b56e] to thread [main] //绑定session到ThreadLocal
2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.support.TransactionSynchronizationManager - Initializing transaction synchronization
2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.interceptor.TransactionInterceptor - Getting transaction for [cn.javass.common.service.impl.BaseService.countAll]
2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.support.TransactionSynchronizationManager - Retrieved value [org.springframework.orm.hibernate4.SessionHolder@1184a4f] for key [org.hibernate.internal.SessionFactoryImpl@107b56e] bound to thread [main]
2012-03-07 09:58:44 [main] DEBUG org.springframework.orm.hibernate4.HibernateTransactionManager - Found thread-bound Session 

2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.support.TransactionSynchronizationManager - Retrieved value [org.springframework.orm.hibernate4.SessionHolder@1184a4f] for key [org.hibernate.internal.SessionFactoryImpl@107b56e] bound to thread [main]
Hibernate: 
    select
        count(*) as col_0_0_ 
    from
        tbl_user usermodel0_

2012-03-07 09:58:44 [main] DEBUG org.springframework.orm.hibernate4.HibernateTransactionManager - Committing Hibernate transaction on Session    //提交事务

2012-03-07 09:58:44 [main] DEBUG org.springframework.transaction.support.TransactionSynchronizationManager - Removed value [org.springframework.orm.hibernate4.SessionHolder@1184a4f] for key [org.hibernate.internal.SessionFactoryImpl@107b56e] from thread [main] //解除绑定session到ThreadLocal

 

到此我们可以看到事务起作用了，也就是说即使把@Transactional放到接口上 基于JDK动态代理也是可以工作的。

 

 

三、基于CGLIB类代理：

 

java代码：

<tx:annotation-driven transaction-manager="txManager" proxy-target-class="true"/>

<tx:annotation-driven transaction-manager="txManager" proxy-target-class="true"/>

   该配置方式是基于CGLIB类代理

 

启动测试会报错，No Session found for current thread，说明事务没有起作用

 

java代码：

org.hibernate.HibernateException: No Session found for current thread
    at org.springframework.orm.hibernate4.SpringSessionContext.currentSession(SpringSessionContext.java:97)
    at org.hibernate.internal.SessionFactoryImpl.getCurrentSession(SessionFactoryImpl.java:1024)
    at cn.javass.common.dao.hibernate4.BaseHibernateDao.getSession(BaseHibernateDao.java:63)
    at cn.javass.common.dao.hibernate4.BaseHibernateDao.aggregate(BaseHibernateDao.java:238)
    at cn.javass.common.dao.hibernate4.BaseHibernateDao.countAll(BaseHibernateDao.java:114)
    at cn.javass.common.service.impl.BaseService.countAll(BaseService.java:60)
    at cn.javass.common.service.impl.BaseService$$FastClassByCGLIB$$5b04dd69.invoke(<generated>)
    at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:149)
    at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:618)
    at cn.javass.demo.service.impl.UserServiceImpl$$EnhancerByCGLIB$$7d46c567.countAll(<generated>)
    at cn.javass.ssonline.spider.service.impl.UserServiceTest2.testCreate(UserServiceTest2.java:20)

org.hibernate.HibernateException: No Session found for current thread
    at org.springframework.orm.hibernate4.SpringSessionContext.currentSession(SpringSessionContext.java:97)
    at org.hibernate.internal.SessionFactoryImpl.getCurrentSession(SessionFactoryImpl.java:1024)
    at cn.javass.common.dao.hibernate4.BaseHibernateDao.getSession(BaseHibernateDao.java:63)
    at cn.javass.common.dao.hibernate4.BaseHibernateDao.aggregate(BaseHibernateDao.java:238)
    at cn.javass.common.dao.hibernate4.BaseHibernateDao.countAll(BaseHibernateDao.java:114)
    at cn.javass.common.service.impl.BaseService.countAll(BaseService.java:60)
    at cn.javass.common.service.impl.BaseService$$FastClassByCGLIB$$5b04dd69.invoke(<generated>)
    at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:149)
    at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:618)
    at cn.javass.demo.service.impl.UserServiceImpl$$EnhancerByCGLIB$$7d46c567.countAll(<generated>)
    at cn.javass.ssonline.spider.service.impl.UserServiceTest2.testCreate(UserServiceTest2.java:20)

 

 

如果将注解放在具体类上或具体类的实现方法上才会起作用。

 

java代码：

package cn.javass.common.service.impl;
public abstract class BaseService<M extends java.io.Serializable, PK extends java.io.Serializable> implements IBaseService<M, PK> {

   @Transactional()   //放在抽象类上
    @Override
    public int countAll() {
        return baseDao.countAll();
    }
}

package cn.javass.common.service.impl;
public abstract class BaseService<M extends java.io.Serializable, PK extends java.io.Serializable> implements IBaseService<M, PK> {
 
   @Transactional()   //放在抽象类上
    @Override
    public int countAll() {
        return baseDao.countAll();
    }
}

 

运行测试类，将发现成功了，因为我们的UserService继承该方法，但如果UserService覆盖该方法，如下所示，也将无法织入事务(报错)：

 

java代码：

package cn.javass.demo.service.impl;
public class UserServiceImpl extends BaseService<UserModel, Integer> implements UserService {
    //没有@Transactional
    @Override
    public int countAll() {
        return baseDao.countAll();
    }
}

package cn.javass.demo.service.impl;
public class UserServiceImpl extends BaseService<UserModel, Integer> implements UserService {
    //没有@Transactional
    @Override 
    public int countAll() {
        return baseDao.countAll();
    }
}

 

 

四、基于aspectj的

 

java代码：

<tx:annotation-driven transaction-manager="txManager" mode="aspectj" proxy-target-class="true"/>

<tx:annotation-driven transaction-manager="txManager" mode="aspectj" proxy-target-class="true"/>

在此就不演示了，我们主要分析基于JDK动态代理和CGLIB类代理两种的区别。

 

五、结论：

基于JDK动态代理 ，可以将@Transactional放置在接口和具体类上。

基于CGLIB类代理，只能将@Transactional放置在具体类上。

 

因此 在实际开发时全部将@Transactional放到具体类上，而不是接口上。

 

六、分析

1、  JDK动态代理

1.1、Spring使用JdkDynamicAopProxy实现代理：

 

java代码：

package org.springframework.aop.framework;
final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
    //注意此处的method 一定是接口上的method（因此放置在接口上的@Transactional是可以发现的）
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    }
}

package org.springframework.aop.framework;
final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
    //注意此处的method 一定是接口上的method（因此放置在接口上的@Transactional是可以发现的）
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    }
}

注意此处的method 一定是接口上的method（因此放置在接口上的@Transactional是可以发现的）

 

1.2、如果<tx:annotation-driven 中 proxy-target-class="true" ，Spring将使用CGLIB动态代理，而内部通过Cglib2AopProxy实现代理，而内部通过DynamicAdvisedInterceptor进行拦截：

 

java代码：

package org.springframework.aop.framework;
final class Cglib2AopProxy implements AopProxy, Serializable {
    private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {
            //注意此处的method 一定是具体类上的method（因此只用放置在具体类上的@Transactional是可以发现的）
        public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
            }
       }
}

package org.springframework.aop.framework;
final class Cglib2AopProxy implements AopProxy, Serializable {
	private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {
            //注意此处的method 一定是具体类上的method（因此只用放置在具体类上的@Transactional是可以发现的）
	    public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
            }
       }
}

 

1.3、Spring使用AnnotationTransactionAttributeSource通过查找一个类或方法是否有@Transactional注解事务来返回TransactionAttribute（表示开启事务）：

 

java代码：

package org.springframework.transaction.annotation;
public class AnnotationTransactionAttributeSource extends AbstractFallbackTransactionAttributeSource implements Serializable {
         protected TransactionAttribute determineTransactionAttribute(AnnotatedElement ae) {
        for (TransactionAnnotationParser annotationParser : this.annotationParsers) {
            TransactionAttribute attr = annotationParser.parseTransactionAnnotation(ae);
            if (attr != null) {
                return attr;
            }
        }
        return null;
    }
}

package org.springframework.transaction.annotation;
public class AnnotationTransactionAttributeSource extends AbstractFallbackTransactionAttributeSource implements Serializable {
         protected TransactionAttribute determineTransactionAttribute(AnnotatedElement ae) {
		for (TransactionAnnotationParser annotationParser : this.annotationParsers) {
			TransactionAttribute attr = annotationParser.parseTransactionAnnotation(ae);
			if (attr != null) {
				return attr;
			}
		}
		return null;
	}
}

而AnnotationTransactionAttributeSource又使用SpringTransactionAnnotationParser来解析是否有@Transactional注解：

 

 

java代码：

package org.springframework.transaction.annotation;

public class SpringTransactionAnnotationParser implements TransactionAnnotationParser, Serializable {

    public TransactionAttribute parseTransactionAnnotation(AnnotatedElement ae) {
        Transactional ann = AnnotationUtils.getAnnotation(ae, Transactional.class);
        if (ann != null) {
            return parseTransactionAnnotation(ann);
        }
        else {
            return null;
        }
    }

    public TransactionAttribute parseTransactionAnnotation(Transactional ann) {

    }

}

package org.springframework.transaction.annotation;

public class SpringTransactionAnnotationParser implements TransactionAnnotationParser, Serializable {

	public TransactionAttribute parseTransactionAnnotation(AnnotatedElement ae) {
		Transactional ann = AnnotationUtils.getAnnotation(ae, Transactional.class);
		if (ann != null) {
			return parseTransactionAnnotation(ann);
		}
		else {
			return null;
		}
	}

	public TransactionAttribute parseTransactionAnnotation(Transactional ann) {
		
    }

}

 

    此处使用AnnotationUtils.getAnnotation(ae, Transactional.class)； 这个方法只能发现当前方法/类上的注解，不能发现父类的注解。 Spring还提供了一个 AnnotationUtils.findAnnotation()方法 可以发现父类/父接口中的注解（但spring没有使用该接口）。

 

   如果Spring此处换成AnnotationUtils.findAnnotation()，将可以发现父类/父接口中的注解。

 

 

 

 

这里还一个问题，描述如下：

 

在接口中删除@Transactional   //开启默认事务

 

 

java代码：

package cn.javass.common.service;
public interface IBaseService<M extends java.io.Serializable, PK extends java.io.Serializable> {
    public int countAll();
}

package cn.javass.common.service;
public interface IBaseService<M extends java.io.Serializable, PK extends java.io.Serializable> {
    public int countAll();
}  

 

在具体类中添加@Transactional

 

 

java代码：

package cn.javass.common.service.impl;
public abstract class BaseService<M extends java.io.Serializable, PK extends java.io.Serializable> implements IBaseService<M, PK> {

    @Transactional()   //开启默认事务
    @Override
    public int countAll() {
        return baseDao.countAll();
    }
}

package cn.javass.common.service.impl;
public abstract class BaseService<M extends java.io.Serializable, PK extends java.io.Serializable> implements IBaseService<M, PK> {

    @Transactional()   //开启默认事务
    @Override
    public int countAll() {
        return baseDao.countAll();
    }
}

 

 

 

 

 

问题：

    我们之前说过，基于JDK动态代理时， method 一定是接口上的method（因此放置在接口上的@Transactional是可以发现的），但现在我们放在具体类上，那么Spring是如何发现的呢？？

    还记得发现TransactionAttribute是通过AnnotationTransactionAttributeSource吗？具体看步骤1.3：

 

而AnnotationTransactionAttributeSource 继承AbstractFallbackTransactionAttributeSource

 

java代码：

package org.springframework.transaction.interceptor;
public abstract class AbstractFallbackTransactionAttributeSource implements TransactionAttributeSource {

    public TransactionAttribute getTransactionAttribute(Method method, Class<?> targetClass) {
        //第一次 会委托给computeTransactionAttribute
}

    //计算TransactionAttribute的
    private TransactionAttribute computeTransactionAttribute(Method method, Class<?> targetClass) {

        //省略

        // Ignore CGLIB subclasses - introspect the actual user class.
        Class<?> userClass = ClassUtils.getUserClass(targetClass);
        // The method may be on an interface, but we need attributes from the target class.
        // If the target class is null, the method will be unchanged.
        //①此处将查找当前类覆盖的方法
        Method specificMethod = ClassUtils.getMostSpecificMethod(method, userClass);
        // If we are dealing with method with generic parameters, find the original method.
        specificMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);

        // First try is the method in the target class.
        TransactionAttribute txAtt = findTransactionAttribute(specificMethod);
        if (txAtt != null) {
            return txAtt;
        }

        //找类上边的注解
        // Second try is the transaction attribute on the target class.
        txAtt = findTransactionAttribute(specificMethod.getDeclaringClass());
        if (txAtt != null) {
            return txAtt;
        }
        //②如果子类覆盖的方法没有 再直接找当前传过来的
        if (specificMethod != method) {
            // Fallback is to look at the original method.
            txAtt = findTransactionAttribute(method);
            if (txAtt != null) {
                return txAtt;
            }
            // Last fallback is the class of the original method.
            return findTransactionAttribute(method.getDeclaringClass());
        }
        return null;
    }
}

package org.springframework.transaction.interceptor;
public abstract class AbstractFallbackTransactionAttributeSource implements TransactionAttributeSource {

	public TransactionAttribute getTransactionAttribute(Method method, Class<?> targetClass) {
		//第一次 会委托给computeTransactionAttribute
}

    //计算TransactionAttribute的
	private TransactionAttribute computeTransactionAttribute(Method method, Class<?> targetClass) {
		
		//省略

		// Ignore CGLIB subclasses - introspect the actual user class.
		Class<?> userClass = ClassUtils.getUserClass(targetClass);
		// The method may be on an interface, but we need attributes from the target class.
		// If the target class is null, the method will be unchanged.
		//①此处将查找当前类覆盖的方法
		Method specificMethod = ClassUtils.getMostSpecificMethod(method, userClass);
		// If we are dealing with method with generic parameters, find the original method.
		specificMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);

		// First try is the method in the target class.
		TransactionAttribute txAtt = findTransactionAttribute(specificMethod);
		if (txAtt != null) {
			return txAtt;
		}

		//找类上边的注解
		// Second try is the transaction attribute on the target class.
		txAtt = findTransactionAttribute(specificMethod.getDeclaringClass());
		if (txAtt != null) {
			return txAtt;
		}
		//②如果子类覆盖的方法没有 再直接找当前传过来的
		if (specificMethod != method) {
			// Fallback is to look at the original method.
			txAtt = findTransactionAttribute(method);
			if (txAtt != null) {
				return txAtt;
			}
			// Last fallback is the class of the original method.
			return findTransactionAttribute(method.getDeclaringClass());
		}
		return null;
	}
}

 

 

       //①此处将查找子类覆盖的方法

       Method specificMethod = ClassUtils.getMostSpecificMethod(method, userClass);

 

        // ClassUtils.getMostSpecificMethod

       public static Method getMostSpecificMethod(Method method, Class<?> targetClass) {

       Method specificMethod = null;

       if (method != null && isOverridable(method, targetClass) &&

              targetClass != null && !targetClass.equals(method.getDeclaringClass())) {

           try {

              specificMethod = ReflectionUtils.findMethod(targetClass, method.getName(), method.getParameterTypes());

           } catch (AccessControlException ex) {

              // security settings are disallowing reflective access; leave

              // 'specificMethod' null and fall back to 'method' below

           }

       }

       return (specificMethod != null ? specificMethod : method);

    }

 

    可以看出将找到当前类的那个方法。因此我们放置在BaseService countAll方法上的@Transactional起作用了。

 

 

      //②如果子类覆盖的方法没有 再直接找当前传过来的

       if (specificMethod != method) {

           // Fallback is to look at the original method.

           txAtt = findTransactionAttribute(method);

           if (txAtt != null) {

              return txAtt;

           }

           // Last fallback is the class of the original method.

           return findTransactionAttribute(method.getDeclaringClass());

       }

 

       查找子类失败时直接使用传过来的方法。

 

 

 

 

因此，建议大家使用基于Schema风格的事务（不用考虑这么多问题，也不用考虑是类还是方法）。而@Transactional建议放置到具体类上，不要放置到接口。