附件下载出错

程序：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@page import="java.io.*" %>
<%@page import="java.util.Hashtable" %>

<%
     
       String filename=request.getParameter("filename");
     
       if(filename==null)return;
       OutputStream streamOut=response.getOutputStream();
       InputStream streamIn=getServletContext().getResourceAsStream(filename);
       int len = 0;
       byte[] buffer = new byte[2048];
       response.setContentType("application/force-download");
       String name=filename.substring(filename.lastIndexOf("/")+1 );
       response.setHeader("Content-Disposition", "attachment;filename=\""+name +"\" ");

      
       while ((len = streamIn.read(buffer)) > 0) {
         streamOut.write(buffer, 0, len);
       }
       streamIn.close();
       streamOut.close();
      
%>

出错信息:
2008-10-28 21:41:20 org.apache.catalina.core.StandardWrapperValve invoke
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:604)
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:186)
at org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:118)
at org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:77)
at org.apache.jsp.downloads_jsp._jspService(downloads_jsp.java:92)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
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.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Unknown Source)

解决方法：主要是JSP里的OUT流没有关闭。
在streamOut.close();后加
out.clear();
out = pageContext.pushBody();
就OK。