一句话记录--IllegalStateException: getOutputStream() has already been called for this response

IllegalStateException: getOutputStream() has already been called for this response

11-Jun-2017 22:42:21.832 严重 [http-nio-8080-exec-3] org.apache.catalina.core.ApplicationDispatcher.invoke Servlet.service() for servlet jsp threw exception
 java.lang.IllegalStateException: getOutputStream() has already been called for this response
	at org.apache.catalina.connector.Response.getWriter(Response.java:609)
	at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:211)
	at javax.servlet.ServletResponseWrapper.getWriter(ServletResponseWrapper.java:109)
	at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:118)
	at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:111)
	at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:176)
	at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:120)
	at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:75)
	at org.apache.jsp.WEB_002dINF.views.webApp.uploadFtp.uploadPage_jsp._jspService(uploadPage_jsp.java:166)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:726)
	at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:592)
	at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:526)
	at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:160)
	at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
	at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1244)
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:868)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:85)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	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)

SpringMVC 项目中进行下载操做时，后台想在经过 OutputStream 生成文件后跳转至下载结束页面，并提示下载结果，发现后台运行后提示该错误。查阅资料后发现是因为 web 容器生成的 servlet 代码中有out.write()，这个会和 JSP 中调用的 response.getOutputStream() 产生冲突.。Servlet 规范提到，不能既调用 response.getOutputStream()，又调用 response.getWriter()，不管先调用哪个，在调用第二个时候就会抛出 IllegalStateException。

在查阅了网上众多帖子后，测试发现后台控制器中下载文件时若出现该 Exception 则能够经过返回 null 来进行处理。