Servlet会在服务器启动或第一次请求该Servlet的时候开始生命周期,在服务器结束的时候结束生命周期。无论请求多少次Servlet,最多只有一个Servlet实例。多个客户端并发请求Servlet时,服务器会启动多个线程分别执行该Servlet的service()方法。
一、重点方法说明
1.init(ServletConfig conf)
加载Servlet时运行此方法,如果load-on-startup为0,则客户端第一次请求该Servlet时加载Servlet,如果load-on-startup配置为1,则容器启动时加载Servlet。
2.Service(ServletRequest req, ServletResponse res)
客户端每次请求Servlet都会运行该方法,该方法判断访问类型,然后根据HttpServletRequest的getMethod()返回结果判断是执行doGet还是doPost,doPut等。
3.destroy()
卸载Servlet时执行该方法,当容器关闭时会先卸载所有的Servlet,因此容器关闭时会执行destroy方法。
二、例子实践
1.web.
1 <!-- Servlet生命周期演示 -->2 <servlet>3 <servlet-name>LifeCycleServlet</servlet-name>4 <servlet-class>com.servlet.LifeCycleServlet</servlet-class>5 </servlet>6 <servlet-mapping>7 <servlet-name>LifeCycleServlet</servlet-name>8 <url-pattern>/servlet/LifeCycleServlet</url-pattern>9 </servlet-mapping>
2.LifeCycleServlet
1 package com.servlet; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 6 import javax.servlet.ServletConfig; 7 import javax.servlet.ServletException; 8 import javax.servlet.http.HttpServlet; 9 import javax.servlet.http.HttpServletRequest;10 import javax.servlet.http.HttpServletResponse;11 12 public class LifeCycleServlet extends HttpServlet {13 14 private double startPoint;15 16 /**17 * Destruction of the servlet. <br>18 */19 public void destroy() {20 this.log("执行destroy()方法...");21 // Put your code here22 }23 24 public void doGet(HttpServletRequest request, HttpServletResponse response)25 throws ServletException, IOException {26 this.log("执行doGet()方法...");27 response.setContentType("text/html");28 response.setCharacterEncoding("UTF-8");29 PrintWriter out = response.getWriter();30 out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");31 out.println("<HTML>");32 out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");33 out.println(" <BODY>");34 out.println("<form method='post'>");35 out.println("<div align='center'>");36 out.print("<h1>Servlet 生命周期(1)</h1></br>");37 out.println("<input type='submit' value='点我'>");38 out.println("</div>");39 out.println("</form>");40 out.println(" </BODY>");41 out.println("</HTML>");42 out.flush();43 out.close();44 45 }46 47 public void doPost(HttpServletRequest request, HttpServletResponse response)48 throws ServletException, IOException {49 this.log("执行doPost()方法...");50 response.setContentType("text/html");51 response.setCharacterEncoding("UTF-8");52 PrintWriter out = response.getWriter();53 out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");54 out.println("<HTML>");55 out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");56 out.println(" <BODY>");57 out.println("<div align='center'>");58 out.print("<h1>Servlet 生命周期(2)</h1></br>");59 out.println("<input type='button' onclick='history.go(-1)' value='返回上一级'>");60 out.println("</div>");61 out.println(" </BODY>");62 out.println("</HTML>");63 out.flush();64 out.close();65 66 }67 68 public void service(HttpServletRequest request,HttpServletResponse response)69 throws ServletException, IOException {70 this.log("执行service()方法...");71 super.service(request, response);72 }73 74 public void init() throws ServletException {75 // Put your code here76 this.log("执行init()方法...");77 }78 79 }
3.效果图
浏览器:
控制台输出:
原标题:Java Web开发之Servlet生命周期
关键词:JAVA