Jsp通过文件流实现文件下载

<%@ page contentType="application/x-xls;charset=GBK"%>
<%@ page import="java.io.File,java.io.FileInputStream"%>
<%@ page import="javax.servlet.ServletOutputStream"%>
<%
//若使用字节流进行文件下载，应该首先清空一下out对象，默认是字符流
out.clear();
out = pageContext.pushBody();
//通过设置头标题来显示文件传送到前端浏览器的文件信息
response.setHeader("Content-disposition","inline;filename=test.xls");
File file = new File("D:/","test.xls");
response.setHeader("Content_Length",String.valueOf(file.length()));
FileInputStream input = null;
ServletOutputStream output = null;
try{
   input = new FileInputStream(file);
   output = response.getOutputStream();
   byte size[] = new byte[1024];
   int length;
   while((length=input.read(size))!=-1){
    output.write(size);
   }
}catch(Exception e){
   System.out.print(e.getMessage());
}finally{
   try{
    input.close();
    output.flush();
    output.close();
   }catch(Exception ex){
 
   }
}

%>