java 下载出错 400 请求报错 

各位路过的朋友，帮帮怎么解决以下问题
严重: 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:611)  at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:198)  at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:125)  at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:118)  at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:188)  at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:118)  at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:77)  at org.apache.jsp.error_jsp._jspService(error_jsp.java:86)  at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)  at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)  at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:386)  at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)  at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)  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.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646)  at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)  at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)  at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)  at org.apache.struts2.dispatcher.ServletDispatcherResult.doExecute(ServletDispatcherResult.java:157)  at org.apache.struts2.dispatcher.StrutsResultSupport.execute(StrutsResultSupport.java:186)  at com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:373)  at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:277)  at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)  at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:498)  at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)  at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)  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:102)  at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:554)  at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)  at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)  at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)  at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)  at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)  at java.lang.Thread.run(Thread.java:662)