SpringAOP功能扩展报错：java.lang.ClassCastException: class com.sun.proxy.$Proxy16 cannot be cast to class x
前言：
- 如果想直接得到解决办法的话，请直接跳转到解决。
报错：
- java.lang.ClassCastException: class com.sun.proxy.$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
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@Overridepublic 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");}@Overrideprotected 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@Overridepublic 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");}@Overrideprotected 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。
