json数据响应有问题，不懂，是报了什么错？

DEBUG [http-nio-8081-exec-10] - DispatcherServlet with name 'dispatcherServlet' processing POST request for [/ssm0712_war_exploded/user1/testAjax.do]
DEBUG [http-nio-8081-exec-10] - Looking up handler method for path /user1/testAjax.do
DEBUG [http-nio-8081-exec-10] - Returning handler method [public com.zhongruan.bean.User com.zhongruan.controller.UserController.testAjax(com.zhongruan.bean.User)]
DEBUG [http-nio-8081-exec-10] - Returning cached instance of singleton bean 'userController'
DEBUG [http-nio-8081-exec-10] - Skip CORS processing: request is from same origin
DEBUG [http-nio-8081-exec-10] - Failed to resolve argument 0 of type 'com.zhongruan.bean.User'
org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'application/json;charset=UTF-8' not supported
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver.readWithMessageConverters(AbstractMessageConverterMethodArgumentResolver.java:226)
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.readWithMessageConverters(RequestResponseBodyMethodProcessor.java:157)
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.resolveArgument(RequestResponseBodyMethodProcessor.java:130)
    at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:124)
    at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:161)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:131)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:871)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:777)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:881)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:652)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:888)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1597)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)
DEBUG [http-nio-8081-exec-10] - Resolving exception from handler [public com.zhongruan.bean.User com.zhongruan.controller.UserController.testAjax(com.zhongruan.bean.User)]: org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'application/json;charset=UTF-8' not supported
DEBUG [http-nio-8081-exec-10] - Resolving exception from handler [public com.zhongruan.bean.User com.zhongruan.controller.UserController.testAjax(com.zhongruan.bean.User)]: org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'application/json;charset=UTF-8' not supported
DEBUG [http-nio-8081-exec-10] - Resolving exception from handler [public com.zhongruan.bean.User com.zhongruan.controller.UserController.testAjax(com.zhongruan.bean.User)]: org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'application/json;charset=UTF-8' not supported
DEBUG [http-nio-8081-exec-10] - Null ModelAndView returned to DispatcherServlet with name 'dispatcherServlet': assuming HandlerAdapter completed request handling
DEBUG [http-nio-8081-exec-10] - Successfully completed request

script标签

     //页面加载，绑定单击事件
        $(function (){
            $("#btn").click(function (){
                //alert("hello btn");
                //发送ajax请求
                $.ajax({
                    //编写json格式，设置属性和值
                    url:"./user1/testAjax.do",
                    contentType:"application/json;charset=UTF-8",
                    data:'{"username":"hehe","password":"123","age":30}',
                    dataType:"json",
                    type:"post",
                    success:function (data){
                        //data服务器端响应的json的数据，进行解析
                        alert(data);
                        alert(data.username);
                        alert(data.password);
                    }
                });
            });
        });

controller代码

 @RequestMapping("/testAjax")
    public @ResponseBody User testAjax(@RequestBody User user){
        System.out.println("testAjax方法执行了.....");
        //客户端发送ajax的请求，传的是json字符串，后端吧json字符串封装到user对象中
        System.out.println(user);
        //做响应，模拟数据库查询
        user.setUsername("hhhh");
        user.setAge(44);
        //做响应
        return user;
    }

你的实体类是不是有问题呀，尤其看看有没有时间属性，类型有没有错以及get set方法是不是有问题
去掉 implements Serializable 没什么用,还有你的前端不该写字符串，因为你接受的是一个对象啊，data应该这样写，其实不该加单引号，不加的话就是对象啦

data:{"username":"hehe","password":"123","age":30},

这个是直接传对象object，不是传字符串吧；
data:{ username:'username',password: 'password',age: '999'}