Spring com.sun.proxy.$Proxy6 cannot be cast to

今天在带领学生做spring声明式事务时，部分同学的程序报错com.sun.proxy.$Proxy6 cannot be cast to。下面就详细介绍一下这个错误的原因及解决方法。

一、工程结构图

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
	xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx.xsd">
	<bean id="ds" class="com.mchange.v2.c3p0.ComboPooledDataSource">
		<property name="jdbcUrl" value="jdbc:oracle:thin:@192.168.1.104:1521:icss" />
		<property name="driverClass" value="oracle.jdbc.OracleDriver" />
		<property name="user" value="scott" />
		<property name="password" value="icss" />
		<property name="initialPoolSize" value="3" />
		<property name="maxPoolSize" value="10" />
		<property name="minPoolSize" value="1" />
		<property name="acquireIncrement" value="3" />
		<property name="maxIdleTime" value="60" />
	</bean>
	<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
		<property name="dataSource" ref="ds"></property>
	</bean>
	<bean id="userDaoImpl" class="dao.UserDaoImpl">
		<property name="jdbcTemplate" ref="jdbcTemplate"></property>
	</bean>
	<bean id="userServiceImpl" class="service.UserServiceImpl">
		<property name="user" ref="userDaoImpl"></property>
	</bean>
	<bean id="transactionManager"
		class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
		<property name="dataSource" ref="ds"></property>
	</bean>
	<tx:advice id="txTransactionManager" transaction-manager="transactionManager">
		<tx:attributes>
			<tx:method name="update*" isolation="DEFAULT" propagation="REQUIRED"	read-only="false" />
			<tx:method name="delete*" isolation="DEFAULT" propagation="REQUIRED"	read-only="false" />
			<tx:method name="insert*" isolation="DEFAULT" propagation="REQUIRED"   read-only="false" />
			<tx:method name="find*" read-only="true" />
			<tx:method name="read*" read-only="true" />
			<tx:method name="load*" read-only="true" />
		</tx:attributes>
	</tx:advice>

	<aop:config>
		<aop:pointcut expression="within(service.*)" id="txPointCut"></aop:pointcut>
		<aop:advisor advice-ref="txTransactionManager"	pointcut-ref="txPointCut"></aop:advisor>
	</aop:config>


</beans>

TestUser:

package config;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import service.IUserService;
import service.UserServiceImpl;

public class TestUser {

	/**
	 * @param args
	 */
	@Test
	public void insert(){
		
		ApplicationContext ac=new ClassPathXmlApplicationContext("config/applicationContext.xml");
		IUserService user=(UserServiceImpl) ac.getBean("userServiceImpl");
		user.insertBatch();
	}
}

二、错误原因

       Spring AOP实现方式有两种，一种使用JDK动态代理，另一种通过CGLIB来为目标对象创建代理。如果被代理的目标实现了至少一个接口，则会使用JDK动态代理，所有该目标类型实现的接口都将被代理。若该目标对象没有实现任何接口，则创建一个CGLIB代理，创建的代理类是目标类的子类。

       显然，本工程中是通过JDK动态代理来实现AOP的。

三、解决方法

       1.在applicationContext.xml中增加下面内容，来强制使用CGLIB创建代理。

	<strong><aop:aspectj-autoproxy proxy-target-class="true"/> </strong>
	<aop:config>
		<aop:pointcut expression="within(service.*)" id="txPointCut"></aop:pointcut>
		<aop:advisor advice-ref="txTransactionManager"	pointcut-ref="txPointCut"></aop:advisor>
	</aop:config>

      2.ac.getBean("userServiceImpl")前强制类型改成接口

	public void insert(){
		
		ApplicationContext ac=new ClassPathXmlApplicationContext("config/applicationContext.xml");
		IUserService user=<strong>(IUserService)</strong> ac.getBean("userServiceImpl");
		user.insertBatch();
	}