Servlet的三种实现方式

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第一种：实现javax.servlet.Servlet接口
显见要实现接口未实现的方法。
Java：

package d0322_01_Servlet;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.Servlet;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class servletDemo1 implements Servlet{    public servletDemo1(){        System.out.println("这是构造方法！");    }    @Override    public void destroy() {        System.out.println("销毁");           }    @Override    public ServletConfig getServletConfig() {        // TODO Auto-generated method stub        return null;    }    @Override    public String getServletInfo() {        System.out.println("没啥用");        return "没啥用";    }    @Override    public void init(ServletConfig arg0) throws ServletException {        System.out.println("这是初始化！");    }    @Override    public void service(ServletRequest arg0, ServletResponse arg1)throws ServletException, IOException {        System.out.println("服务");        PrintWriter pw = arg1.getWriter();        pw.write("Hello!");    }}

第二种：继承javax.servet.GenericServlet类(适配器模式)
Java：

package d0321_01_servlet;import java.io.IOException;import javax.servlet.GenericServlet;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class ServletDemo2 extends GenericServlet{    @Override    public void service(ServletRequest arg0, ServletResponse arg1)            throws ServletException, IOException {        System.out.println("服务！");          }}

第三种：继承javax.servlet.http.HttpServlet类（模板方法设计模式）
Java：

package d0321_01_servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class ServletDemo3 extends HttpServlet{    @Override    // 1.处理GET请求    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        System.out.println("---------doGet---------");    }    @Override    //1.处理Post请求    protected void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        System.out.println("---------doPost---------");     }}

.Xml

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">  <!--创建一个Servlet实例  -->  <servlet>        <servlet-name>servletDemo1</servlet-name>        <servlet-class>d0321_01_servlet.ServletDemo1</servlet-class>        <!-- 让Servlet在服务器启动时就创建 -->        <load-on-startup>2</load-on-startup>  </servlet>  <!-- 给Servlet提供(映射)一个可供客户端访问的URI -->  <servlet-mapping>     <servlet-name>servletDemo1</servlet-name>    <url-pattern>/demo1</url-pattern>  </servlet-mapping>  <!--创建一个Servlet实例  -->  <servlet>        <servlet-name>ServletDemo2</servlet-name>        <servlet-class>d0321_01_servlet.ServletDemo2</servlet-class>  </servlet>  <!-- 给Servlet提供一个可供客户端访问的URI -->  <servlet-mapping>        <servlet-name>ServletDemo2</servlet-name>        <url-pattern>/Demo2</url-pattern>  </servlet-mapping> <!--创建一个servlet实例  --> <servlet>        <servlet-name>ServletDemo3</servlet-name>        <servlet-class>d0321_01_servlet.ServletDemo3</servlet-class> </servlet> <!-- 给servlet提供一个可供客户端访问的URI --> <servlet-mapping>        <servlet-name>ServletDemo3</servlet-name>        <url-pattern>/Demo3</url-pattern> </servlet-mapping></web-app>

小提示：Servlet是底层的接口（要实现的方法太多，不常用）
GenericServlet类实现了Servlet接口（只需重写service，也不常用）
HttpServlet类实现了GenericServlet类（只需重写doGet与doPOST，常用）

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