做一个jsp下载excel的功能，功能描述如下：首先将excel下载到服务器，然后从服务器下载到本地。
最开始是一个页面，点击下载，用ajax跳转到后台，将文件下载到服务器，然后跳回jsp，执行如下js：
if(xmlHttpRequest.status==200){//服务器状态码
var loadDir = "/webrpt/loadFile.jsp?flag=1&dir=BBSJ_DOWNLOAD.zip" ;
window.location.href (loadDir) ;
}
此时跳转到下载jsp页面，自动弹出下载窗口,下载jsp loadFile.JSP代码如下：
[code="java"]
<%@ page contentType="text/html;charset=GBK" %>
<%@ page import="java.io.*" %>
<%
java.io.BufferedInputStream bis=null;
java.io.BufferedOutputStream bos=null;
try{
String filename=request.getParameter("dir");
response.reset();
File fileLoad=new File("D://",request.getParameter("dir"));
filename=new String(filename.getBytes("iso8859-1"),"gbk");
response.setContentType("application/x-download");
response.setHeader("Content-disposition","attachment; filename="+new String(filename.getBytes("gbk"),"iso8859-1"));
bis=new java.io.BufferedInputStream(new java.io.FileInputStream(fileLoad));
bos=new java.io.BufferedOutputStream(response.getOutputStream());
byte[] buff = new byte[2048];
int bytesRead;
while(-1 != (bytesRead = bis.read(buff, 0, buff.length))){
bos.write(buff,0,bytesRead);
}
bos.flush();
}catch(Exception e){
e.printStackTrace();
}finally{
if(bis != null)bis.close();
if(bos != null)bos.close();
}%>
[/code]
加断点显示，当弹出下载窗口的时候还没报错，再执行之后的outputstream出错，错误信息如下:
严重: Servlet.service() for servlet debugjsp threw exception
java.lang.IllegalStateException: getOutputStream() has already been called for this response
at org.apache.catalina.connector.Response.getWriter(Response.java:596)
at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:186)
at org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:124)
at org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:117)
at org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:191)
at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:115)
at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:75)
at org.apache.jsp.loadFile_jsp._jspService(org.apache.jsp.loadFile_jsp:84)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:322)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:291)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:856)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:744)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:595)
整了一天了，一直没有解决。。。。
