springMVC 集成 jquery ajax

        最近在研究springMVC框架，做测试demo时添加ajax异步请求时出现问题，现在贴出请求端源码

<script type="text/javascript" src="./js/jquery-1.10.2.js"></script>
  <script type="text/javascript">
  	function testLogin(){
  	
  	alert("sdfs");
  	$.ajax({
	type: "get",
	url: "./login.do",
	dataType: "json",
    data: {
     loginName: "111",loginPassword:"222"
    },
	
	beforeSend: function(XMLHttpRequest){
	//ShowLoading();
		alert("beforeSend");
	},
	success: function(data, textStatus){
		alert(data);
	},
	complete: function(XMLHttpRequest, textStatus){
	//HideLoading();
		alert("Complete");
	},
	error: function(XMLHttpRequest, textStatus, errorThrown){
	//请求出错处理
		 alert(XMLHttpRequest.status);
         alert(XMLHttpRequest.readyState);
         alert(textStatus);
	}
	}); 	
  	
  	}
  </script>

 能够成功请求后台，但是，在后台的controller处理过程中出现错误。经查找，觉得是springMVC框架没有加入json支持，所以去掉dataType: "json", 就用默认字符串传值，前台正常显示，可是控制台报错。

10:46:41,625  WARN DefaultHandlerExceptionResolver:127 - Handling of [org.springframework.web.HttpMediaTypeNotAcceptableException] resulted in Exception
java.lang.IllegalStateException
	at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:421)
	at org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.handleHttpMediaTypeNotAcceptable(DefaultHandlerExceptionResolver.java:219)
	at org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.doResolveException(DefaultHandlerExceptionResolver.java:103)
	at org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver.resolveException(AbstractHandlerExceptionResolver.java:136)
	at org.springframework.web.servlet.DispatcherServlet.processHandlerException(DispatcherServlet.java:1060)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:884)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:792)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:851)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:756)
	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 org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
	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:103)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
	at java.lang.Thread.run(Thread.java:662)
2013-9-24 10:46:41 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet springMVC-flex threw exception
org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation
	at org.springframework.web.servlet.mvc.method.annotation.support.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:181)
	at org.springframework.web.servlet.mvc.method.annotation.support.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:146)
	at org.springframework.web.servlet.mvc.method.annotation.support.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:103)
	at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:64)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:113)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:502)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:465)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:863)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:792)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:851)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:756)
	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 org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
	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:103)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
	at java.lang.Thread.run(Thread.java:662)

 于是再次查找错误，后度娘告诉我：servlet代码中有out.write(””)，这个和JSP中缺省调用的response.getOutputStream()产生冲突.
因为在jsp中，out变量是通过response.getWriter得到的，在程序中既用了 response.getOutputStream，又用了out变量，故出现以上错误，没办法只有

try {
  
			    PrintWriter out = response.getWriter();    
			    out.println("ceshi ajax");   
			    out.flush();
			    out.close();

		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		mv.addObject("ajax测试！");
		mv.setViewName("login");
		return null;

 reutrn null 变得正常，不知道大神们是怎么处理这个问题的呢？