Servlet有三种实现方式：

* 实现Servlet接口

* 继承GenericServlet类

* 继承HttpServlet类

1.实现servlet类

package com.vc.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 HelloWorldServlet implements Servlet{	//释放内存	//1. reload	//2. 关闭TomCat	//3. 关机	public void destroy() {		// TODO Auto-generated method stub		System.out.println("destroy it");	}	public ServletConfig getServletConfig() {		// TODO Auto-generated method stub		return null;	}	public String getServletInfo() {		// TODO Auto-generated method stub		return null;	}	//该 函数用于初始化，只会被调用一次（当用户第一次访问Servlet时，被调用）	public void init(ServletConfig arg0) throws ServletException {		// TODO Auto-generated method stub		System.out.println("init it");			}	//用于处理业务逻辑，应该把业务逻辑代码写在该方法中	//会被多次调用，当用户每访问一次时就会被调用一次	//request用于获取客户端的信息	//response用户向客户端返回信息	public void service(ServletRequest request, ServletResponse response)			throws ServletException, IOException {		// TODO Auto-generated method stub		System.out.println("service it");		PrintWriter printWriter=response.getWriter();		printWriter.println("
"+"hello,world"+"
");			}}

2.继承 genericservlet

package com.vc.servlet;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.GenericServlet;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;@SuppressWarnings("serial")public class HelloWorldGenericServlet extends GenericServlet {	@Override	public void service(ServletRequest request, ServletResponse response)			throws ServletException, IOException {		// TODO Auto-generated method stub		try{			PrintWriter printWriter=response.getWriter();			printWriter.println("
hello,generic world.!!!
");		}catch(Exception e){			e.printStackTrace();		}	}}

3.继承httpServlet

package com.vc.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;@SuppressWarnings("serial")public class HelloWorldHttpServlet extends HttpServlet {	@Override	protected void doGet(HttpServletRequest req, HttpServletResponse resp)			throws ServletException, IOException {		// TODO Auto-generated method stub		doPost(req,resp);				}	@Override	protected void doPost(HttpServletRequest req, HttpServletResponse resp)			throws ServletException, IOException {		// TODO Auto-generated method stub				PrintWriter printWriter=resp.getWriter();		printWriter.println("
Hello World!
");		}}