java.lang.IllegalStateException: Cannot call sendError() after the response has been committed

最近项目中有这样一个需求，先获取文件服务器上相应的文件列表，然后在线预览各个文件，这样就需要即时的生成文件的二进制流数据，我采用的实现方式是：使用response写二进制文件流，结果是：文件可以实现在线预览，且预览成功，但是实现控制台中跑出了异常：java.lang.IllegalStateException: Cannot call sendError() after the response has been committed 和 org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation。报错信息如下：

2019-05-21 20:27:53 [http-nio-8800-exec-10] WARN  o.s.w.s.m.s.DefaultHandlerExceptionResolver - Failure while trying to resolve exception [org.springframework.web.HttpMediaTypeNotAcceptableException]
java.lang.IllegalStateException: Cannot call sendError() after the response has been committed
	at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:472)
	at javax.servlet.http.HttpServletResponseWrapper.sendError(HttpServletResponseWrapper.java:129)
	at com.alibaba.druid.support.http.WebStatFilter$StatHttpServletResponseWrapper.sendError(WebStatFilter.java:342)
	at org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.handleHttpMediaTypeNotAcceptable(DefaultHandlerExceptionResolver.java:304)
	at org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.doResolveException(DefaultHandlerExceptionResolver.java:181)
	at org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver.resolveException(AbstractHandlerExceptionResolver.java:139)
	at org.springframework.web.servlet.handler.HandlerExceptionResolverComposite.resolveException(HandlerExceptionResolverComposite.java:80)
	at org.springframework.web.servlet.DispatcherServlet.processHandlerException(DispatcherServlet.java:1297)
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1109)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1055)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	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 com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:123)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at com.sophon.szc.log.framework.CORSFilter.doFilter(CORSFilter.java:33)
	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.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
	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.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92)
	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.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93)
	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.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:200)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1415)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$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)
2019-05-21 20:27:53 [http-nio-8800-exec-10] ERROR o.a.c.c.C.[.[.[.[dispatcherServlet] - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Could not find acceptable representation] with root cause
org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation
	at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:307)
	at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:180)
	at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:82)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:119)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	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 com.alibaba.druid.support.http.WebStatFilter.doFilter(WebStatFilter.java:123)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at com.sophon.szc.log.framework.CORSFilter.doFilter(CORSFilter.java:33)
	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.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
	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.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92)
	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.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93)
	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.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:200)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1415)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:748)
2019-05-21 20:27:53 [http-nio-8800-exec-10] ERROR o.s.b.a.w.s.e.ErrorMvcAutoConfiguration$StaticView - Cannot render error page for request [/test/list/detail] and exception [Could not find acceptable representation] as the response has already been committed. As a result, the response may have the wrong status code.

经过多方查找资料，有的说是接口返回类型不匹配，有的说是静态文件名跟控制器请求路由冲突，还有说接口请求数据对象转换错误，以上所有原因都不是我这个异常的真正症状。

最后通过多次调整，最终有了解决思路：

首先重点关注异常信息：java.lang.IllegalStateException: Cannot call sendError() after the response has been committed，

字面上是参数异常， 在response已经提交之后 不能发送错误请求。

来看我的代码实现：

   /**
    *
    * controller层方法
    */

    @RequestMapping(value = "/list/detail", method = RequestMethod.GET)
    public ApiResultWrapper> viewOnline(HttpServletRequest request, HttpServletResponse response) {

        String fileName = request.getParameter("fileName");
        // 这里是根据url在线预览文件，在service层通过response写二进制的文件流实现
        reportPictureService.viewFile(fileName, response);

        // 这里是导致异常的问题点，为什么呢？在后面描述
        return ApiResponse.success();
    }

    /**
     * service 层方法预览文件
     *
     * @param fileName 文件名
     * @param response response
     */
    public void viewFile(String fileName, HttpServletResponse response) {
        try {
            // 省略部分代码，就是正常建立文件路径连接的过程

            response.setHeader("Content-Disposition", "inline;filename=" + fileName);
            OutputStream out = response.getOutputStream();
            while ((len = is.read(buff)) > 0) {
                out.write(buff, 0, len);
            }
            out.flush();
            
            // 下面这句是导致异常的第二个点
            out.close();
            is.close();
        } catch (IOException e) {
            log.error("在线预览文件异常，fileName = {}", fileName);
        }
    }

所以导致异常的原因解释如下：

首先，利用reponse.getWrite()获得输出流对象，close()之后，这里reponse其实已经提交了。

然后，方法回到controller 层，后面还有一句 return ApiResponse.success()，执行之后发现response已经进行已经跳转了，只不过url没有发生改变，并且页面上也不会生成返回的响应数据。所以当执行上面的return代码之后 ，reponse 会提交两次，服务器就不知道该怎么办了，就抛出异常。

解决方案：

第一步：去掉service层的out.close()  这里不会因为PrintWriter 输出对象没有关闭而占用资源的。

第二步：去掉controller层的return，这个就是在线预览文件，并不需要接口返回任何响应数据，多此一举，反而还导致了异常发生。

附上最终代码：

   /**
    *
    * controller层方法
    */
    @RequestMapping(value = "/list/detail", method = RequestMethod.GET)
    public void viewOnline(HttpServletRequest request, HttpServletResponse response) {

        String fileName = request.getParameter("fileName");
        reportPictureService.viewFile(fileName, response);
    }

    /**
     * service 层方法预览文件
     *
     * @param fileName 文件名
     * @param response response
     */
    public void viewFile(String fileName, HttpServletResponse response) {
        try {
            // 省略部分代码，就是正常建立文件路径连接的过程

            response.setHeader("Content-Disposition", "inline;filename=" + fileName);
            OutputStream out = response.getOutputStream();
            while ((len = is.read(buff)) > 0) {
                out.write(buff, 0, len);
            }
            out.flush();
            is.close();
        } catch (IOException e) {
            log.error("在线预览文件异常，fileName = {}", fileName);
        }
    }