用java实现文件下载，提示java.lang.IllegalStateException: getOutputStream() has already been called for this response

1、 用java实现文件下载，提示java.lang.IllegalStateException: getOutputStream() has already been called for this response

2、代码如下


3、控制台提示信息图



4、解决方案是：在给处理下载文件转发的jsp页面，添加

<%
out.clear();
out = pageContext.pushBody();
%>