servlet设置缓存时间以及文件的下载

缓存时间的设置：

 public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         response.setContentType("text/html;charset=UTF-8");
         PrintWriter out = response.getWriter();
         response.setDateHeader("Expires", System.currentTimeMillis()+60*60*1000);//缓存时间一小时
         out.write("hello world");
 }

通知客户端文件的下载，此处以图片为例：

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         response.setContentType("text/html");
         ServletContext context=getServletContext();

         String path=context.getRealPath("/picture.jpg");
         String fileName=path.substring(path.lastIndexOf("\\")+1);
         InputStream in=new FileInputStream(path);

         //通知客户端文件的下载    URLEncoder.encode解决文件名中文的问题
         response.setHeader("Content-Disposition", "attachment;filename="+URLEncoder.encode(fileName, "utf-8"));
         response.setHeader("Content-Type", "application/octet-stream");

         OutputStream out=response.getOutputStream();
         int length=-1;
         byte []buffer=new byte[1024];
         while((length=in.read(buffer))!=-1){
             out.write(buffer,0,length);
         }
         in.close();
     }