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  Servlet - 自动页面刷新

  • 简述

    考虑显示实时游戏分数或股票市场状态或货币兑换比率的网页。对于所有此类页面，您需要使用浏览器的刷新或重新加载按钮定期刷新网页。
    Java Servlet 为您提供了一种机制，您可以在其中制作网页，使其在给定的时间间隔后自动刷新，从而使这项工作变得容易。
    刷新网页最简单的方法是使用方法 setIntHeader()响应对象。以下是此方法的签名 - 
    
public void setIntHeader(String header, int headerValue)
    此方法将标头“Refresh”连同一个整数值一起发送回浏览器，该整数值指示以秒为单位的时间间隔。

  • 自动页面刷新示例

    此示例显示 servlet 如何使用 setIntHeader() 设置方法 Refresh 标题。 
    
// Import required java libraries
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
 
// Extend HttpServlet class
public class Refresh extends HttpServlet {
 
   // Method to handle GET method request.
   public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
      
      // Set refresh, autoload time as 5 seconds
      response.setIntHeader("Refresh", 5);
 
      // Set response content type
      response.setContentType("text/html");
 
      // Get current time
      Calendar calendar = new GregorianCalendar();
      String am_pm;
      int hour = calendar.get(Calendar.HOUR);
      int minute = calendar.get(Calendar.MINUTE);
      int second = calendar.get(Calendar.SECOND);
      
      if(calendar.get(Calendar.AM_PM) == 0)
        am_pm = "AM";
      else
        am_pm = "PM";
 
      String CT = hour+":"+ minute +":"+ second +" "+ am_pm;
    
      PrintWriter out = response.getWriter();
      String title = "Auto Page Refresh using Servlet";
      String docType =
         "<!doctype html public \"-//w3c//dtd html 4.0 " + "transitional//en\">\n";
      
      out.println(docType +
         "<html>\n" +
         "<head><title>" + title + "</title></head>\n"+
         "<body bgcolor = \"#f0f0f0\">\n" +
         "<h1 align = \"center\">" + title + "</h1>\n" +
         "<p>Current Time is: " + CT + "</p>\n"
      );
   }
   
   // Method to handle POST method request.
   public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
      
      doGet(request, response);
   }
}
    现在让我们编译上面的 servlet 并在 web.xml 中创建以下条目 
    
....
 <servlet>
     <servlet-name>Refresh</servlet-name>
     <servlet-class>Refresh</servlet-class>
 </servlet>
 
 <servlet-mapping>
     <servlet-name>Refresh</servlet-name>
     <url-pattern>/Refresh</url-pattern>
 </servlet-mapping>
....
    现在使用 URL http://localhost:8080/Refresh 调用这个 servlet，它将在每 5 秒后显示当前系统时间，如下所示。只需运行 servlet 并等待查看结果 -
    Current Time is: 9:44:50 PM
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