org.springframework.web.HttpMediaTypeNotAcceptableException:

From：http://cmzx3444.iteye.com/blog/930732

js代码： 

function ajaxLogin() {
    $.ajax({type:"post"
, url:
"ajaxLogin.do"
, data:
"username=acid&password=acid"
, success:function (account) {
        alert("Data Saved: "
 + account.username);
    }});
}

Controller中的方法： 

@RequestMapping
(value = 
"/ajaxLogin.do"
, method = RequestMethod.POST)
public
 
@ResponseBody
Account ajaxLogin(HttpServletRequest request, @Valid
Account account, BindingResult result)
{
    account = accountService.getAccount(account.getUsername(), account.getPassword());
    if
 (account == 
null
)
    {
        return
 
null
;
    }
    Utils.setToSession(SessionKey.USER_ID, account.getUsername());
    return
 account;
}

结果出现了这个异常： 

org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter$ServletHandlerMethodInvoker.writeWithMessageConverters(AnnotationMethodHandlerAdapter.java:993
)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter$ServletHandlerMethodInvoker.handleResponseBody(AnnotationMethodHandlerAdapter.java:933
)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter$ServletHandlerMethodInvoker.getModelAndView(AnnotationMethodHandlerAdapter.java:882
)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:428
)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414
)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790
)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719
)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644
)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549
)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:617
)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717
)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290
)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206
)
    at com.shop.core.context.ContextInitFilter.doFilter(ContextInitFilter.java:33
)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235
)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206
)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233
)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191
)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127
)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102
)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109
)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298
)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857
)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588
)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489
)
    at java.lang.Thread.run(Thread.java:662
)

看了看官方的demo，好像用到了jackson这个包。加上这个包后一切正常！ 
原因估计是序列化这个account对象的时候出了问题。因为我直接返回string对象不会出错。