1.什么是servlet ？

servlet是java运行在服务器端的应用程序，本质是java 类库

2.servlet的作用是什么？

接收客户端的请求，处理请求，给出响应

3.如何创建servlet

1）继承HttpServlet 或者实现Servlet接口

2）

web.xml 配置Servlet映射：

<servlet>
<servlet-name>BookServlet</servlet-name>
<servlet-class>com.servlet.deno.BookServlet</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>BookServlet</servlet-name>
<url-pattern>/servlet/BookServlet</url-pattern>
</servlet-mapping>

或者使用注解

@WebServlet(name="bookServlet",urlPatterns="/demo/book") 

4.Servlet的生命周期

以继承HttpServlet接口为例

1）实例化Servlet对象, 第一次请求的时候实例化，只会实例化一次（说明servlet是单例的，线程不安全的，成员变量的使用需要谨慎）

2）执行初始化init ，第一次请求的时候，只执行一次

3）当请求来临的时候，Service方法根据请求类型不同，分发请求doGet，doPost，doPut...

4） doGet,doPost处理请求，给出响应

5）销毁Servlet，容器关闭的时候，执行destory

 

 

package com.servlet.deno;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(name="bookServlet",urlPatterns="/demo/book")
public class BookServlet extends HttpServlet {

    /**
     * Constructor of the object.
     */
    public BookServlet() {
        System.out.println("-----------servlet instance----------------");
    }
    
    
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        
        System.out.println("----------service 分发请求---------");
        super.service(req, resp);
    }
    
    

    /**
     * Destruction of the servlet. <br>
     */
    public void destroy() {
        System.out.println("******************************************");
        System.out.println("-----------------destory----------------");
    }

    /**
     * The doGet method of the servlet. <br>
     *
     * This method is called when a form has its tag value method equals to get.
     * 
     * @param request the request send by the client to the server
     * @param response the response send by the server to the client
     * @throws ServletException if an error occurred
     * @throws IOException if an error occurred
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        System.out.println("-------------doGet----------------");
    }

    /**
     * The doPost method of the servlet. <br>
     *
     * This method is called when a form has its tag value method equals to post.
     * 
     * @param request the request send by the client to the server
     * @param response the response send by the server to the client
     * @throws ServletException if an error occurred
     * @throws IOException if an error occurred
     */
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("----------------doPost------------------");
        doGet(request, response);
    }

    /**
     * Initialization of the servlet. <br>
     *
     * @throws ServletException if an error occurs
     */
    public void init() throws ServletException {
        System.out.println("---------------servlet init---------------");
    }

}

控制台输出：

INFO: Deployment of web application directory D:\tomcat\apache-tomcat-7.0.72\webapps\Servlet has finished in 1,291 ms
二月 21, 2020 3:02:38 下午 org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["http-bio-8088"]
二月 21, 2020 3:02:38 下午 org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["ajp-bio-8089"]
二月 21, 2020 3:02:38 下午 org.apache.catalina.startup.Catalina start
INFO: Server startup in 2435 ms
-----------servlet instance----------------
---------------servlet init---------------
----------service 分发请求---------
-------------doGet----------------
二月 21, 2020 3:02:47 下午 org.apache.catalina.core.StandardServer await
INFO: A valid shutdown command was received via the shutdown port. Stopping the Server instance.
二月 21, 2020 3:02:47 下午 org.apache.coyote.AbstractProtocol pause
INFO: Pausing ProtocolHandler ["http-bio-8088"]
二月 21, 2020 3:02:47 下午 org.apache.coyote.AbstractProtocol pause
INFO: Pausing ProtocolHandler ["ajp-bio-8089"]
二月 21, 2020 3:02:47 下午 org.apache.catalina.core.StandardService stopInternal
INFO: Stopping service Catalina
******************************************
-----------------destory----------------