Servlets - 自动刷新( Auto Refresh)
考虑一个显示实时游戏得分或股票市场状态或货币兑换率的网页。 对于所有此类类型的页面，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，您可以通过这种机制创建一个网页，使其在给定的时间间隔后自动刷新。
刷新网页的最简单方法是使用响应对象的方法setIntHeader() 。 以下是此方法的签名 -
public void setIntHeader(String header, int headerValue)
此方法将标题“Refresh”发送回浏览器以及一个整数值，该值表示以秒为单位的时间间隔。
自动页面刷新示例
此示例显示了servlet如何使用setIntHeader()方法执行自动页面刷新以设置Refresh标头。
// 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调用此servlet，它将显示每5秒后的当前系统时间，如下所示。 只需运行servlet并等待查看结果 -
<h1 align="center">Auto Page Refresh using Servlet</h1>
<p>Current Time is: 9:44:50 PM</p>
