ERROR 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:601) at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:196) 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:185) at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:116) at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:76) at org.apache.jsp.InforSystem.download_jsp._jspService(download_jsp.java:67) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:210) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:151) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:870) at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665) at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528) at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81) at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685) at java.lang.Thread.run(Thread.java:595) 出現這種情況，雖然不影響文件夾的下載，但是在後臺出現這種信息還是令人不太舒服。解決方法是：java代碼的<%%>之外不要有空格。如：
<%@ page contentType="text/html;charset=GBK" language="java" import="java.util.*,java.sql.*,com.comingnet.db.*" pageEncoding="GBK"%>
<jsp:directive.page import="com.jspsmart.upload.SmartUpload" /><%
SmartUpload smart=new SmartUpload();// 初始化
smart.initialize(pageContext);
// 設定contentdisposition爲null以禁止瀏覽器自動打開文件，
//保證點擊鏈接後是下載文件。若不設定，則下載的文件擴展名爲
//doc時，瀏覽器將自動用word打開它。擴展名爲pdf時，
//瀏覽器將用acrobat打開。
String filename=request.getParameter("filename");
smart.setContentDisposition(null);
smart.downloadFile("InforSystem/uploadFile/"+filename);
%>