簡述Servlet生命週期

時間 2019-11-13

原文原文鏈接

Servlet生命週期的三個核心方法分別是 init() , service() 和 destroy()。每一個Servlet都會實現這些方法，而且在特定的運行時間調用它們。html

1)在Servlet生命週期的初始化階段，web容器經過調用init()方法來初始化Servlet實例，而且能夠傳遞一個實現 javax.servlet.ServletConfig 接口的對象給它。這個配置對象（configuration object）使Servlet可以讀取在web應用的web.xml文件裏定義的名值（name-value）初始參數。這個方法在Servlet實例的生命週期裏只調用一次。java

2)初始化後，Servlet實例就能夠處理客戶端請求了。web容器調用Servlet的service()方法來處理每個請求。service() 方法定義了可以處理的請求類型而且調用適當方法來處理這些請求。編寫Servlet的開發者必須爲這些方法提供實現。若是發出一個Servlet沒實現的請求，那麼父類的方法就會被調用而且一般會給請求方（requester）返回一個錯誤信息。web

一般，咱們不須要重寫（override）這個方法。網絡

3)最後，web容器調用destroy()方法來終結Servlet。若是你想在Servlet的生命週期內關閉或者銷燬一些文件系統或者網絡資源，你能夠調用這個方法來實現。destroy() 方法和init()方法同樣，在Servlet的生命週期裏只能調用一次。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"; } }

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