JavaWeb学习记录（一）——response响应头之缓存设置与下载功能的实现

一、HTTP中常用响应头

Location: http://www.it315.org/index.jsp
Server:apache tomcat
Content-Encoding: gzip
Content-Length: 80
Content-Language: zh-cn
Content-Type: text/html; charset=GB2312
Last-Modified: Tue, 11 Jul 2000 18:23:51 GMT
Refresh: 1;url=http://www.it315.org
Content-Disposition: attachment; filename=aaa.zip
Transfer-Encoding: chunked
Set-Cookie:SS=Q0=5Lb_nQ; path=/search
ETag: W/"7777-1242234904000"
Expires: -1
Cache-Control: no-cache
Pragma: no-cache
Connection: close/Keep-Alive
Date: Tue, 11 Jul 2000 18:23:51 GMT

二、设置缓存信息

　　public void doGet(HttpServletRequest request, HttpServletResponse response)
           throws ServletException, IOException {
       System.out.println("-----------CacheServlet-------------");
       // 设置相应头信息
       // 设置缓存时间100秒
       // response.setDateHeader("Expires",
       // System.currentTimeMillis()+100*1000);
       // 禁止使用缓存
       // response.setDateHeader("Expires", 0);
       // response.setHeader("Cache-Control", "no-cache");
       // response.setHeader("Pragma", "no-cache");

       response.setContentType("text/html");
       PrintWriter out = response.getWriter();
       out.println("<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">");
       out.println("<HTML>");
       out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
       out.println(" <BODY>");
       // 读取文件
       String path = getServletContext().getRealPath("/a.txt");
       FileReader reader = new FileReader(new File(path));
       char buffer[] = new char[256];
       int len = 0;
       while ((len = reader.read(buffer)) != -1) {
           out.println(new String(buffer, 0, len));
       }
       reader.close();
       out.println(" </BODY>");
       out.println("</HTML>");
       out.flush();
       out.close();
   }

   /**
   * 最后一次修改的时间
   */
   @Override
   protected long getLastModified(HttpServletRequest req) {
       String path = getServletContext().getRealPath("/a.txt");
       File file = new File(path);
       return file.lastModified();
   }

a.txt文件内容：

a.txt在项目中的放置地址：

结果：

三、下载功能源代码如下

public class DownServlet extends HttpServlet {

   public void doGet(HttpServletRequest request, HttpServletResponse response)
           throws ServletException, IOException {
       String path = request.getServletContext().getRealPath("/down/中国.png");
       File file = new File(path);
       // 下载的方式打开此操作（指定编码方式，下载文件名与源文件一致）
       response.addHeader("Content-Disposition", "attachment;fileName="
               + URLEncoder.encode(file.getName(), "UTF-8"));
       OutputStream os = response.getOutputStream();
       InputStream is = new FileInputStream(file);
       int len = 0;
       byte[] buffer = new byte[1024];
       while ((len = is.read(buffer)) != -1) {
           os.write(buffer, 0, len);
       }
       is.close();
       os.close();
   }

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

}

本程序中下载文件的地址放置在该项目的如下位置：