WEB文件下载

String path=request.getServletContext().getRealPath("/download");
System.out.println(path);
String name=request.getParameter("filename");

File file=new File(path,name);
if(file.exists()){
    response.setContentType("application/octet-stream");
    response.setHeader("Content-Disposition","attachment;filename="+name);
    InputStream inputStream = new FileInputStream(file);
    ServletOutputStream os = response.getOutputStream();
（

OutputStream os = response.getOutputStream();
os.write(FileUtils.readFileToByteArray(file));

）
    byte[] car=new byte[1024];
    int len=0;
    while ((len=inputStream.read(car))!=-1){
        os.write(car,0,len);
    }

}
else {
    response.getWriter().println("文件不存在！");
}
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不能请求转发或者重定向，否则无法下载