SpringAOP功能扩展报错：java.lang.ClassCastException: class com.sun.proxy.$Proxy16 cannot be cast to class x

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2022-04-17

前言：

  • 如果想直接得到解决办法的话，请直接跳转到解决。

报错：

  • java.lang.ClassCastException: class com.sun.proxy.$Proxy16 cannot be cast to class xxxx
17-Apr-2022 01:00:07.007 严重 [RMI TCP Connection(3)-127.0.0.1] org.apache.catalina.core.StandardContext.loadOnStartup Servlet [com.zer.controller.LoginServlet] in web application [/account] threw load() exception
 java.lang.ClassCastException: class com.sun.proxy.$Proxy16 cannot be cast to class com.zer.service.impl.LoginServiceImpl (com.sun.proxy.$Proxy16 and com.zer.service.impl.LoginServiceImpl are in unnamed module of loader org.apache.catalina.loader.ParallelWebappClassLoader @12b1cdd2)
	at com.zer.controller.LoginServlet.init(LoginServlet.java:36)
	at javax.servlet.GenericServlet.init(GenericServlet.java:158)
	at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1144)
	at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1091)
	at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:983)
	at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4978)
	at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5290)
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
	at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:754)
	at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
	at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
	at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1736)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:300)
	at java.management/com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:809)
	at java.management/com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
	at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:482)
	at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:431)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:300)
	at java.management/com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:809)
	at java.management/com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
	at java.management/com.sun.jmx.remote.security.MBeanServerAccessController.invoke(MBeanServerAccessController.java:468)
	at java.management.rmi/javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1466)
	at java.management.rmi/javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1307)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at java.management.rmi/javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1406)
	at java.management.rmi/javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:827)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at java.rmi/sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:359)
	at java.rmi/sun.rmi.transport.Transport$1.run(Transport.java:200)
	at java.rmi/sun.rmi.transport.Transport$1.run(Transport.java:197)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at java.rmi/sun.rmi.transport.Transport.serviceCall(Transport.java:196)
	at java.rmi/sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:562)
	at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:796)
	at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:677)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at java.rmi/sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:676)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at java.base/java.lang.Thread.run(Thread.java:834)

代码：

配置文件 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:aop="http://www.springframework.org/schema/aop"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/aop
       http://www.springframework.org/schema/aop/spring-aop.xsd
">

    <!--配置 数据源 bean-->
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/spring?characterEncoding=utf8&amp;serverTimezone=UTC"/>
        <property name="username" value="root"/>
        <property name="password" value="root"/>
    </bean>

    <!--配置 工厂 bean-->
    <bean id="factory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
    </bean>

    <!--配置 mapper扫描 bean-->
    <bean id="mapper" class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="sqlSessionFactory" ref="factory"/>
        <property name="basePackage" value="com.zer.mapper"/>
    </bean>

    <!--配置 业务层 bean-->
    <bean id="loginService" class="com.zer.service.impl.LoginServiceImpl">
        <!--配置用户登录mapper-->
        <property name="loginMapper" ref="loginMapper"/>
    </bean>

    <!--配置 通知 bean-->
    <bean id="before" class="com.zer.advice.MyBefore"/>
    <bean id="after" class="com.zer.advice.MyAfter"/>

    <!--配置 AOP组装规则-->
    <aop:config>
        <aop:pointcut id="my" expression="execution(* com.zer.service.impl.LoginServiceImpl.userLoginService(String,String))"/>
        <aop:advisor advice-ref="before" pointcut-ref="my"/>
        <aop:advisor advice-ref="after" pointcut-ref="my"/>
    </aop:config>

</beans>

LoginServlet.java

package com.zer.controller;

import com.zer.pojo.User;
import com.zer.service.LoginService;
import com.zer.service.impl.LoginServiceImpl;
import org.springframework.context.ApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

/**
 * ClassName: LoginServlet
 * Time: 2022-04-15 16:41
 * Description:
 *
 * @author YZ
 */
@WebServlet(value = "/userLogin",loadOnStartup = 1)
public class LoginServlet extends HttpServlet {
	private LoginServiceImpl loginService;

	//声明init方法，完成Spring资源的初始化加载
	@Override
	public void init() throws ServletException {
		//获取Spring容器对象
		ApplicationContext ac = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());
		System.out.println(ac);
		//获取业务层对象
		loginService = (LoginServiceImpl) ac.getBean("loginService");
	}

	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		//业务代码
    }
}

原因：

  • 出现这个异常的原因是什么呢？
    • 在我们使用 SpringAOP 进行功能扩展的时候，Spring 是通过动态代理的方式来进行扩展的。
  • 动态代理的方式有两种：
    • 第一种是，jdk 代理
    • 第二种是，cglib 代理
  • Spring 默认使用的代理方式是 JDK 代理方式。

解决：

重点：我们都知道，jdk 代理的方式是基于接口的，也就是说，当创建的一个虚拟对象去扩展的时候，这个虚拟对象是属于我们真实对象所实现的接口的。所以我们在获取代理对象的时候，不应该使用这个接口的实现类来接，也就是真实对象。而是用真实对象所实现的接口来接。

如果上面的不是很理解的话，我简单的说一下该理解：

我们创建一个接口 MyInterface ，这个接口被两个类 TestA 和 TestB 给实现了，此时上面的那种情况，就相当于，我们把 TestA 强行转为 TestB。那肯定就是会报错的，这样会比较好理解。

方案：

方案一：修改 Servlet

  • 把接收对象得到类型该为真实对象所实现的接口

package com.zer.controller;

import com.zer.pojo.User;
import com.zer.service.LoginService;
import com.zer.service.impl.LoginServiceImpl;
import org.springframework.context.ApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

/**
 * ClassName: LoginServlet
 * Time: 2022-04-15 16:41
 * Description:
 *
 * @author YZ
 */
@WebServlet(value = "/userLogin",loadOnStartup = 1)
public class LoginServlet extends HttpServlet {
	private LoginService loginService;

	//声明init方法，完成Spring资源的初始化加载
	@Override
	public void init() throws ServletException {
		//获取Spring容器对象
		ApplicationContext ac = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());
		System.out.println(ac);
		//获取业务层对象
		loginService = (LoginService) ac.getBean("loginService");
	}

	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		//业务代码
    }
}

方案二：修改 applicationcontext.xml

  • 使用 cglib 的代理方式
    • 因为，cglib 的代理形式是继承制的。

<?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:aop="http://www.springframework.org/schema/aop"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/aop
       http://www.springframework.org/schema/aop/spring-aop.xsd
">

    <!--配置 数据源 bean-->
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/spring?characterEncoding=utf8&amp;serverTimezone=UTC"/>
        <property name="username" value="root"/>
        <property name="password" value="root"/>
    </bean>

    <!--配置 工厂 bean-->
    <bean id="factory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
    </bean>

    <!--配置 mapper扫描 bean-->
    <bean id="mapper" class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="sqlSessionFactory" ref="factory"/>
        <property name="basePackage" value="com.zer.mapper"/>
    </bean>

    <!--配置 业务层 bean-->
    <bean id="loginService" class="com.zer.service.impl.LoginServiceImpl">
        <!--配置用户登录mapper-->
        <property name="loginMapper" ref="loginMapper"/>
    </bean>
    <bean id="checkAccountService" class="com.zer.service.impl.CheckAccountServiceImpl">
        <!--配置信息检验mapper-->
        <property name="checkAccountMapper" ref="checkAccountMapper"/>
    </bean>

    <!--配置 通知 bean-->
    <bean id="before" class="com.zer.advice.MyBefore"/>
    <bean id="after" class="com.zer.advice.MyAfter"/>

    <!--配置 AOP组装规则-->
    <aop:config>
        <aop:pointcut id="my" expression="execution(* com.zer.service.impl.LoginServiceImpl.userLoginService(String,String))"/>
        <aop:advisor advice-ref="before" pointcut-ref="my"/>
        <aop:advisor advice-ref="after" pointcut-ref="my"/>
    </aop:config>

    <!--spring默认使用jdk代理方式，这里是开启cglib代理模式-->
    <aop:aspectj-autoproxy proxy-target-class="true"/>

</beans>

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