02Servlet

Servlet

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Servlet（Server Applet）是Java Servlet的简称，称为小服务程序或服务连接器，用Java编写的服务器端程序，具有独立于平台和协议的特性，主要功能在于交互式地浏览和生成数据，生成动态Web内容。

过程：1.客户端发送请求至服务器端；2.服务器将请求信息发送至 Servlet；3.Servlet 生成响应内容并将其传给服务器。响应内容动态生成，通常取决于客户端的请求；4.服务器将响应返回给客户端。

1.实现 Servlet 接口

//Servlet的生命周期:从Servlet被创建到Servlet被销毁的过程
//一次创建，到处服务一个Servlet只会有一个对象，服务所有的请求
/*
 * 1.实例化（使用构造方法创建对象）
 * 2.初始化  执行init方法
 * 3.服务     执行service方法
 * 4.销毁    执行destroy方法
 */
public class ServletDemo1 implements Servlet {
    //public ServletDemo1(){}
     //生命周期方法:当Servlet第一次被创建对象时执行该方法,该方法在整个生命周期中只执行一次
    public void init(ServletConfig arg0) throws ServletException {
                System.out.println("=======init=========");
        }
    //生命周期方法:对客户端响应的方法,该方法会被执行多次，每次请求该servlet都会执行该方法
    public void service(ServletRequest arg0, ServletResponse arg1)
            throws ServletException, IOException {
        System.out.println("service");
    }
    //生命周期方法:当Servlet被销毁时执行该方法
    public void destroy() {
        System.out.println("******destroy**********");
    }
//当停止tomcat时也就销毁的servlet。
    public ServletConfig getServletConfig() {
        return null;
    }
    public String getServletInfo() {
        return null;
    }
}

2、继承 GenericServlet 类

public class ServletDemo2 extends GenericServlet {
    @Override
    public void service(ServletRequest arg0, ServletResponse arg1)
            throws ServletException, IOException {
        System.out.println("service");
    }
}

3、继承 HttpServlet 方法

public class ServletDemo3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        System.out.println("doGet");
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        System.out.println("doPost");
        doGet(req,resp);
    }
}

package com.ahabest.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 MyServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    public MyServlet() {
        super();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("doGet");
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("doPost");
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" id="WebApp_ID" version="4.0">

  <display-name>Servlet_001</display-name>

  <servlet>
      <servlet-name>MyServlet</servlet-name>
      <servlet-class>com.ahabest.servlet.MyServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>MyServlet</servlet-name>
      <url-pattern>/MyServlet</url-pattern>
  </servlet-mapping>

  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>

</web-app>

package com.ahabest.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;
public class MyServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private String message = "Hello Word!";
    public MyServlet() {

    }
    public MyServlet(String message) {
        super();
        this.message = message;
    }
    @Override
    public void init() throws ServletException {
        System.out.println(message);
    }
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html");
        PrintWriter pw = resp.getWriter();
        pw.println("<h1>"+message+"</h1>");
    }
    @Override
    public void destroy() {
        super.destroy();
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" id="WebApp_ID" version="4.0">

  <display-name>Servlet_002</display-name>

  <servlet>
      <servlet-name>MyServlet</servlet-name>
      <servlet-class>com.ahabest.servlet.MyServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>MyServlet</servlet-name>
      <url-pattern>/MyServlet</url-pattern>
  </servlet-mapping>

  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>

</web-app>

package com.ahabest.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class FirstServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html");
        resp.setCharacterEncoding("UTF-8");
        PrintWriter out = resp.getWriter();
        out.println(new Date());
        System.out.println();
        out.println("<html><head>");
        out.println("<title>第一个Servlet</title>");
        out.println("</head><body>");
        out.println("第一个Servlet");
        out.println("</body></html>");
        out.close();
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app>
    <servlet>
        <servlet-name>FirstServlet</servlet-name>
        <servlet-class>com.ahabest.servlet.FirstServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>FirstServlet</servlet-name>
        <url-pattern>/FirstServlet</url-pattern>
    </servlet-mapping>
</web-app>