title: I am getting an exception: java.lang.IllegalStateException: getOutputStream() has already been called for this response
body: <p>I want to write code to download a file which is persisted in my system</p>
  
  <p>Here is my code:</p>
  
  <p>In a controller class I have following mapping</p>
  
  <pre><code>@RequestMapping(value = "/processFile", method = RequestMethod.POST)
      public @ResponseBody ModelAndView downloadFileProcess(
              @RequestParam("file") File originalFile,
              @RequestParam("action") String action, HttpServletResponse response) {
  
          ModelAndView model = new ModelAndView();
          model.setViewName("error");
          System.out.println("");
          System.out.println("Action: "+action);
          model.addObject("message", "Action:" + action);
          try {
              utility.downloadFile(originalFile, response);
              message = "The file was downloaded successfully";
  
          } catch (IOException e) {
              e.printStackTrace();
              message = "The process failed due to following reason: "
                      + e.getMessage();
          } catch (Exception e) {
              e.printStackTrace();
              message = "The process failed due to following reason: "
                      + e.getMessage();
          }
          model.setViewName("success");
          model.addObject("message", message);
          return model;
      }
  </code></pre>
  
  <p>The method in the utility class is below:</p>
  
  <pre><code>public void downloadFile(File originalFile, HttpServletResponse response)
              throws FileNotFoundException, IOException {
  
          response.setHeader("Content-Disposition", "attachment; filename="
                  + originalFile.getName());
          IOUtils.copy(
                  new FileInputStream(new File(String.valueOf(originalFile))),
                  response.getOutputStream());
          response.flushBuffer();
  
      }
  </code></pre>
  
  <p>As I want to download the file, I have to use <code>response.getoutputstream()</code>.</p>
  
  <p>But I am getting the following exception:</p>
  
  <pre>
  java.lang.IllegalStateException: Cannot call sendRedirect() after the response has been committed
      at org.apache.catalina.connector.ResponseFacade.sendRedirect(ResponseFacade.java:482)
      at org.springframework.web.servlet.view.RedirectView.sendRedirect(RedirectView.java:548)
      at org.springframework.web.servlet.view.RedirectView.renderMergedOutputModel(RedirectView.java:279)
      at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:267)
      at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1221)
      at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1005)
      at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:952)
      at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
      at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
      at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
      at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
      at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
      at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
      at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
      at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
      at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
      at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
      at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
      at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
      at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
      at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
      at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1736)
      at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1695)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
      at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
      at java.lang.Thread.run(Thread.java:745)
  
  2015-05-31 12:42:07.547 ERROR 15009 --- [nio-8080-exec-4] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet dispatcherServlet threw exception
  
  java.lang.IllegalStateException: getOutputStream() has already been called for this response
      at org.apache.catalina.connector.Response.getWriter(Response.java:678)
      at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:213)
      at javax.servlet.ServletResponseWrapper.getWriter(ServletResponseWrapper.java:104)
      at org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration$SpelView.render(ErrorMvcAutoConfiguration.java:187)
      at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1221)
      at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1005)
      at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:952)
      at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
      at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
      at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
      at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:101)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
      at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
      at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:604)
      at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:543)
      at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:467)
      at org.apache.catalina.core.StandardHostValve.status(StandardHostValve.java:342)
      at org.apache.catalina.core.StandardHostValve.throwable(StandardHostValve.java:434)
      at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:205)
      at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
      at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
      at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
      at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
      at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
      at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1736)
      at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1695)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
      at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
      at java.lang.Thread.run(Thread.java:745)
  
  2015-05-31 12:42:07.551 ERROR 15009 --- [nio-8080-exec-4] o.a.c.c.C.[Tomcat].[localhost]           : Exception Processing ErrorPage[errorCode=0, location=/error]
  
  org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.IllegalStateException: getOutputStream() has already been called for this response
      at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:973)
      at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
      at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:101)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
      at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
      at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:604)
      at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:543)
      at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:467)
      at org.apache.catalina.core.StandardHostValve.status(StandardHostValve.java:342)
      at org.apache.catalina.core.StandardHostValve.throwable(StandardHostValve.java:434)
      at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:205)
      at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
      at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
      at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
      at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
      at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
      at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1736)
      at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1695)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
      at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
      at java.lang.Thread.run(Thread.java:745)
  Caused by: java.lang.IllegalStateException: getOutputStream() has already been called for this response
      at org.apache.catalina.connector.Response.getWriter(Response.java:678)
      at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:213)
      at javax.servlet.ServletResponseWrapper.getWriter(ServletResponseWrapper.java:104)
      at org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration$SpelView.render(ErrorMvcAutoConfiguration.java:187)
      at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1221)
      at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1005)
      at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:952)
      at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
      at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
      ... 27 common frames omitted
  </pre>