Servelet 简介

 我们可以实现 Servlet接口:

package com.LearnJAVA.Serverlet;

import java.io.IOException;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class helloServlet
 */
@WebServlet("/hello")
public class helloServlet implements Servlet  {
    private static final long serialVersionUID = 1L;
    public helloServlet () {
        System.out.println("constructor");
    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        System.out.println("destroy");
        
    }

    @Override
    public ServletConfig getServletConfig() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public String getServletInfo() {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void init(ServletConfig arg0) throws ServletException {
        // TODO Auto-generated method stub
        System.out.println("init...");
        
    }

    @Override
    public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("service..");
        
    }
       
    

}

Servlet被Servlet容器管理,其生命周期:

1 构造器: 只被调用一次,创建servlet实例. 所以servlet是单实例的.(有线程安全问题)

2 init : 只被调用一次,在servlet被创建之后调用,用于初始化servelet.

3 service: 每次请求时调用,用于响应请求

4 destroy :服务器关闭时调用,用于销毁servlet,释放资源

5 load-on-startup 参数: 

　　当其值大于等于0时, 在启动web项目时,调用servlet构造器和init方法,且值越小越先创建

　　当其值小于0时,在第一次请求时创建