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.对于所有这类类型的页面,您需要使用浏览器的刷新或重新加载按钮定期刷新您的网页.
Java Servlet为您提供了一种机制,使您可以轻松完成这项工作制作一个网页,使其在给定的间隔后自动刷新.
刷新网页的最简单方法是使用方法 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.
此示例显示servlet如何使用 setIntHeader()方法执行自动页面刷新以设置刷新标头.
// 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,这将显示每5次后的当前系统时间秒如下.只需运行servlet并等待查看结果 :
Auto Page Refresh using ServletCurrent Time is: 9:44:50 PM