Servlet的三种实现方式

1.实现Servlet接口的方式

import javax.servlet.*;
public class Hello implements Servlet{
    
    //初始化Servlet
    //该函数只会被调用一次(当用户第一次访问该Servlet时被调用)
    public void init(ServletConfig parm1) throws ServletException {
    
        System.out.println("init it");
    }    
    
    public ServletConfig getServletConfig() {
        
        return null;
    }
    
    //这个函数用于处理业务逻辑
    //程序员应当把业务逻辑代码写在这里
    //当用户每访问一次该servlet时候都会调用
    //reg:用于获得客户端(浏览器)的信息
    //res:用于向客户端(浏览器)返回信息
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
        
        System.out.println("service it");
        //从res中得到printwriter
        PrintWriter pw = res.getWriter();
        pw.println("hello,world!");
    }
    
    public String getServletInfo() {
        
        return "";
    }
    
    //销毁servlet实例(释放内存)
    //1.reload该servlet(webApps)2.关闭tomcat3.关机  (这三种操作都会销毁Servlet)

    public void destroy() {
        System.out.println("destroy!");
        
    }
    
}

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2.通过继承GenericServlet

import javax.servlet.GenericServlet;
import javax.servlet.*;


public class HelloGeneric extends GenericServlet{
    //重写service方法即可
    
    public void service(ServletRequest req,ServletResponse res){
        //返回hello,world!generic
        try{
            PrintWriter pw = res.getWriter();
            pw.println("hello,world!generic");
        }catch(Exception ex){
            ex.printStackTrace();
        }
    }
}

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3.通过继承HttpServlet

import javax.servlet.http.*;

public class HelloHttp extends HttpServlet{
    //处理get请求
    //req:用于获得客户端(浏览器)的信息
    //res:用于向客户端(浏览器)返回信息
    public void doGet(HttpServletRequest req,HttpServletResponse res){
        //业务逻辑
        try{
            PrintWriter pw = res.getWriter();
            pw.println("hello,world!HttpServlet");
        }catch(Exception ex){
            ex.printStackTrace();
        }
    }
    
    //处理post请求
    //req:用于获得客户端(浏览器)的信息
    //res:用于向客户端(浏览器)返回信息
    public void doPost(HttpServletRequest req,HttpServletResponse res){
        this.doGet(req,res);
    }
}