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一、目的

• Servlet接口及其实现类的使用

• Servlet虚拟路径映射的配置

• 使用Eclipse工具开发Servlet

• Servlet的生命周期

二、原理

Servlet由Servlet容器提供，所谓的Servlet容器是指提供了Servlet 功能的服务器（本书中指Tomcat），Servlet容器将Servlet动态的加载到服务器上。

Servlet的生命周期

Servlet的生命周期是指Servlet从被Servlet容器加载、初始化，到处理客户端请求，直至销毁的整个过程。以下是Servlet生命周期的详细介绍：

三、过程

1. TestServlet02文件演示效果

(1) 通过getServletConfig()函数获取初始化参数里面内容。

(2) 通过get()展示获取到的参数内容

2. TestServlet03文件演示效果

(1) 通过getServletContext()函数获取参数内容

(3) 通过get()展示获取到的参数内容

3. TestServlet04与TestServlet05文件演示效果

(1) 文件4设置参数，文件5获取参数

(2) 通过get()展示获取到的参数内容

4. 控制台展示生命周期过程

代码段

四、代码

web.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="https://jakarta.ee/xml/ns/jakartaee" xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd" id="WebApp_ID" version="5.0"><!-- <display-name>chapter03</display-name> --><!-- 3.4.1 小结配置信息 --><servlet><servlet-name>TestServlet02</servlet-name><servlet-class>cn.itcast.servlet.TestServlet02</servlet-class><init-param><param-name>encoding</param-name><param-value>UTF-8</param-value></init-param></servlet><servlet-mapping><servlet-name>TestServlet02</servlet-name><url-pattern>/TestServlet02</url-pattern></servlet-mapping><!-- 3.4.2 配置信息 --><context-param><param-name>companyName</param-name><param-value>itcast</param-value></context-param><context-param><param-name>address</param-name><param-value>beijing</param-value></context-param><servlet><servlet-name>TestServlet03</servlet-name><servlet-class>cn.itcast.servlet.TestServlet03</servlet-class></servlet><servlet-mapping><servlet-name>TestServlet03</servlet-name><url-pattern>/TestServlet03</url-pattern></servlet-mapping><servlet><description></description><display-name>TestServlet04</display-name><servlet-name>TestServlet04</servlet-name><servlet-class>cn.itcast.servlet.TestServlet04</servlet-class></servlet><servlet-mapping><servlet-name>TestServlet04</servlet-name><url-pattern>/TestServlet04</url-pattern></servlet-mapping><servlet><description></description><display-name>TestServlet05</display-name><servlet-name>TestServlet05</servlet-name><servlet-class>cn.itcast.servlet.TestServlet05</servlet-class></servlet><servlet-mapping><servlet-name>TestServlet05</servlet-name><url-pattern>/TestServlet05</url-pattern></servlet-mapping><welcome-file-list><welcome-file>index.html</welcome-file><!--  <welcome-file>index.jsp</welcome-file><welcome-file>index.htm</welcome-file><welcome-file>default.html</welcome-file><welcome-file>default.jsp</welcome-file><welcome-file>default.htm</welcome-file> --></welcome-file-list>
</web-app>  

TestServlet02.java文件

package cn.itcast.servlet;
import java.io.*;import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;public class TestServlet02 extends HttpServlet {/*** */private static final long serialVersionUID = 1L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stub
//		super.doGet(req, resp);PrintWriter out = resp.getWriter();// 获得ServletConfig对象ServletConfig config = this.getServletConfig();// 获得参数名为encoding对应的参数值String param = config.getInitParameter("encoding");out.println("encoding=" + param);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubsuper.doPost(req, resp);}
}

TestServlet03.java文件

package cn.itcast.servlet;
import java.io.*;
import java.util.*;import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;public class TestServlet03 extends HttpServlet {/*** */private static final long serialVersionUID = 1L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubPrintWriter out = resp.getWriter();// 得到ServletContext对象ServletContext context = this.getServletContext();// 得到包含所有初始化参数名的Enumeration对象Enumeration<String> paramNames = context.getInitParameterNames();// 遍历所有的初始化参数名，得到相应的参数值，打印到控制台out.println("all the paramName and paramValue are following:");// 遍历所有的初始化参数名，得到相应的参数值并打印while (paramNames.hasMoreElements()) {String name = paramNames.nextElement();String value = context.getInitParameter(name);out.println(name + ": " + value);out.println("<br>");}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubsuper.doPost(req, resp);}
}

TestServlet04.java文件

package cn.itcast.servlet;
import java.io.*;import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;public class TestServlet04 extends HttpServlet {/*** */private static final long serialVersionUID = 1L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stub
//		super.doGet(req, resp);ServletContext context = this.getServletContext();// 通过setAttribute()方法设置属性值context.setAttribute("data", "this servlet save data");}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubsuper.doPost(req, resp);}
}

TestServlet05.java文件

package cn.itcast.servlet;
import java.io.IOException;
import java.io.PrintWriter;import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;public class TestServlet05 extends HttpServlet {/*** */private static final long serialVersionUID = 1L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stub
//		super.doGet(req, resp);ServletContext context = this.getServletContext();Object object = context.getAttribute("data");PrintWriter out = resp.getWriter();out.println(object.toString());}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubsuper.doPost(req, resp);}
}

SomeServlet.java文件

package com.powernode.servlets;import java.io.IOException;import jakarta.servlet.Servlet;
import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;public class SomeServlet implements Servlet {private ServletConfig config;@Overridepublic void init(ServletConfig config) throws ServletException {// TODO Auto-generated method stubthis.config = config;System.out.println("init");}@Overridepublic ServletConfig getServletConfig() {// TODO Auto-generated method stubreturn config;}@Overridepublic void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {// TODO Auto-generated method stub
//		获取servlet名称String servletName = config.getServletName();System.out.println("获取servlet名称:" + servletName);//		获取servletContext对象ServletContext servletContext = config.getServletContext();System.out.println("获取servletContext对象" + servletContext);
//		获取初始化参数String initParameter1 = config.getInitParameter("name");System.out.println("name:" + initParameter1);System.out.println("service");}@Overridepublic String getServletInfo() {// TODO Auto-generated method stubreturn null;}@Overridepublic void destroy() {// TODO Auto-generated method stubSystem.out.println("destroy()");}}