简述Servlet生命周期

时间 2019-11-13

原文原文链接

Servlet生命周期的三个核心方法分别是 init() , service() 和 destroy()。每一个Servlet都会实现这些方法，而且在特定的运行时间调用它们。html

1)在Servlet生命周期的初始化阶段，web容器经过调用init()方法来初始化Servlet实例，而且能够传递一个实现 javax.servlet.ServletConfig 接口的对象给它。这个配置对象（configuration object）使Servlet可以读取在web应用的web.xml文件里定义的名值（name-value）初始参数。这个方法在Servlet实例的生命周期里只调用一次。java

2)初始化后，Servlet实例就能够处理客户端请求了。web容器调用Servlet的service()方法来处理每个请求。service() 方法定义了可以处理的请求类型而且调用适当方法来处理这些请求。编写Servlet的开发者必须为这些方法提供实现。若是发出一个Servlet没实现的请求，那么父类的方法就会被调用而且一般会给请求方（requester）返回一个错误信息。web

一般，咱们不须要重写（override）这个方法。网络

3)最后，web容器调用destroy()方法来终结Servlet。若是你想在Servlet的生命周期内关闭或者销毁一些文件系统或者网络资源，你能够调用这个方法来实现。destroy() 方法和init()方法同样，在Servlet的生命周期里只能调用一次。ide

以下例子post

package com.wxp.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;this

public class MyFirstServlet extends HttpServlet {
   /**
   * Constructor of the object.
   */
   public MyFirstServlet() {
       super();
   }.net

   /**
   * Destruction of the servlet. <br>
   */
   public void destroy() {
       super.destroy(); // Just puts "destroy" string in log
       // Put your code here
   }code

   /**
   * The doGet method of the servlet. <br>
   *
   * This method is called when a form has its tag value method equals to get.
   *
   * @param request the request send by the client to the server
   * @param response the response send by the server to the client
   * @throws ServletException if an error occurred
   * @throws IOException if an error occurred
   */
   public void doGet(HttpServletRequest request, HttpServletResponse response)
           throws ServletException, IOException {orm

       response.setContentType("text/html;charset=utf-8");
       PrintWriter out = response.getWriter();
       try {
           out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
           out.println("<HTML>");
           out.println(" <HEAD><TITLE>MyFirstServlet</TITLE></HEAD>");
           out.println(" <BODY>");
           out.print("Servlet MyFirstServlet at");
           out.print(request.getContextPath());
           out.println(" </BODY>");
           out.println("</HTML>");
       } catch (Exception e) {
           e.printStackTrace();
       }finally{
           out.flush();
           out.close();
       }
   }

   /**
   * The doPost method of the servlet. <br>
   *
   * This method is called when a form has its tag value method equals to post.
   *
   * @param request the request send by the client to the server
   * @param response the response send by the server to the client
   * @throws ServletException if an error occurred
   * @throws IOException if an error occurred
   */
   public void doPost(HttpServletRequest request, HttpServletResponse response)
           throws ServletException, IOException {
this.doGet(request, response);
   }

/** * Initialization of the servlet. <br> * * @throws ServletException if an error occurs */ public void init() throws ServletException { // Put your code here } public String getServletInfo(){ return "MyFirstServlet"; } }