HTTP 报头设置实例、响应及总结

小灰灰 2024-02-19 12:39 58阅读 0赞

eg:

@WebServlet("/Refresh")
    public class Refresh extends HttpServlet{
    
    	/**
    	 * 
    	 */
    	private static final long serialVersionUID = 1L;
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		//super.doGet(req, resp);
    		// 设置刷新自动加载时间为 5 秒
    		//Refresh:这个头信息指定浏览器应该如何尽快请求更新的页面。您可以指定页面刷新的秒数。
    		resp.setIntHeader("Refresh", 500);
    		System.out.println("req:"+req);
    		System.out.println("resp:"+resp);
    		resp.setContentType("text/html;charset=UTF-8");
    		Calendar calendar=Calendar.getInstance();
    		java.util.Date taskTime=calendar.getTime();
    		SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); 
    		//格式化输出  
            String nowTime = df.format(taskTime);
            PrintWriter out = resp.getWriter();
            String title = "自动刷新 Header 设置 - 菜鸟教程实例";
            String docType =
            "<!DOCTYPE html>\n";
            out.println(docType +
              "<html>\n" +
              "<head><title>" + title + "</title></head>\n"+
              "<body bgcolor=\"#f0f0f0\">\n" +
              "<h1 align=\"center\">" + title + "</h1>\n" +
              "<p>当前时间是：" + nowTime + "</p>\n");
        }
    		
    
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		//super.doPost(req, resp);
    		doGet(req, resp);
    	}
    
    	@Override
    	protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		// TODO Auto-generated method stub
    		super.service(req, resp);
    	}
    	
    }

效果：每隔500秒浏览器页面刷新一次，并显示当前时间。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW9saXViYW8x_size_27_color_FFFFFF_t_70][]

总结：当浏览器第一次向服务器发请求的时候，服务器为请求设置请求头信息，

resp.setIntHeader("Refresh", 500);（本例中）

然后浏览器解析请求头并作出相应的反馈。服务器不会主动向浏览器发消息，只有当浏览器请求的时候服务器才会作出反馈。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW9saXViYW8x_size_27_color_FFFFFF_t_70 1][]

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW9saXViYW8x_size_27_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/4ef0db61f3714ff29ee61960bbfe8217.png