jsp下载压缩文件
<%@ page language="java" import="java.util.*,java.io.*" pageEncoding="GB2312"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <body> <%OutputStream o = response.getOutputStream();%> <% byte b[] = new byte; File fileload = new File("c:/12.rar"); response.setHeader("Content-disposition","attachment;filename=12.rar"); response.setContentType("application/x-tar"); long fileLength = fileload.length(); String length = String.valueOf(fileLength); response.setHeader("Content_Length",length); FileInputStream in = new FileInputStream(fileload); int n = 0; while((n=in.read(b))!=-1){ //o.write(b,0,n); } in.close(); o.flush(); o.close(); out.clear(); out=pageContext.pushBody();%></body></html> 在没加下面两条语句的时候，程序会抛出下面的错误:java.lang.IllegalStateException: getOutputStream() has already been called for this response 产生这样的异常原因:是web容器生成的servlet代码中有out.write(""),这个和JSP中调用的response.getOutputStream()产生冲突.即Servlet规范说明，不能既调用response.getOutputStream()，又调用response.getWriter(),无论先调用哪一个，在调用第二个时候应会抛出IllegalStateException，因为在jsp中，out变量实际上是通过response.getWriter得到的，你的程序中既用了response.getOutputStream，又用了out变量，故出现以上错误。
下面是解决办法:
out.clear(); out=pageContext.pushBody();
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