一句話記錄--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 嚴重 [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 項目中進行下載操做時，後臺想在經過 OutputStream 生成文件後跳轉至下載結束頁面，並提示下載結果，發現後臺運行後提示該錯誤。查閱資料後發現是因爲 web 容器生成的 servlet 代碼中有out.write()，這個會和 JSP 中調用的 response.getOutputStream() 產生衝突.。Servlet 規範提到，不能既調用 response.getOutputStream()，又調用 response.getWriter()，不管先調用哪個，在調用第二個時候就會拋出 IllegalStateException。

在查閱了網上衆多帖子後，測試發現後臺控制器中下載文件時若出現該 Exception 則能夠經過返回 null 來進行處理。