5-servlet简介

一。servlet
1.是什么：java程序来处理页面请求和响应
2.实现方式：
　　a。实现Servlet接口
　　b。继承HttpServlet类

3.步骤：
　　a.创建一个java程序实现Servlet或者继承HttpServlet类
　　b.修改web.xml文件

　　　　<servlet>
　　　　　　<!-- servlet名字，可以自定义 -->
　　　　　　<servlet-name>firstServlet</servlet-name>
　　　　　　<!-- 要执行的servlet程序的完整类名 -->
　　　　　　<servlet-class>com.servlet.FirstServlet</servlet-class>
　　　　</servlet>
　　　　<servlet-mapping>
　　　　　　<servlet-name>firstServlet</servlet-name>
　　　　　　<!-- 访问该servlet的url路径。/表示根目录开始 -->
　　　　　　<url-pattern>/first</url-pattern>
　　　　</servlet-mapping>
　　c.访问：http://localhost:8888/hwua_web/first

4.第二种方式：

　　继承HttpServlet，重写里面的doget和doPost方法
　　　　方法中的参数：req对应request resp对应response
　　　　session的获取方式：HttpSession session = req.getSession();

5.第三种：继承HttpServlet，重写里面的doget和doPost方法
　　在类上写一个注解：@WebServlet("/login3")//此注解代替web.xml的配置文件

实例1：实现 Servlet 接口 +  web.xml注册

　　LoginServlet.java

 package com.control;

 import java.io.IOException;

 import javax.servlet.Servlet;
 import javax.servlet.ServletConfig;
 import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
 import javax.servlet.http.Cookie;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;

 import com.pojo.UserInfo;
 import com.service.IUserInfoService;
 import com.service.UserInfoService;

 public class LoginServlet implements Servlet{
     public void destroy() {

     }
     public ServletConfig getServletConfig() {
         return null;
     }
     public String getServletInfo() {
         return null;
     }
     public void init(ServletConfig arg0) throws ServletException {

     }
     public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException {
         HttpServletRequest req = (HttpServletRequest) arg0;
         HttpServletResponse res = (HttpServletResponse) arg1;
         //获取session
         HttpSession session = req.getSession();

         req.setCharacterEncoding("utf-8");
         String username = req.getParameter("username");
         String password = req.getParameter("password");
         String isrember = req.getParameter("isremder");
         IUserInfoService userSer = new UserInfoService();
         UserInfo user = userSer.login(username, password);
         if(user!=null){
             session.setAttribute("user",user);
             //登录成功，将用户名和密码保存到cookie中
             if("1".equals(isrember)){//记住用户名
                 Cookie cookie = new Cookie("username",user.getUser_name());
                 cookie.setMaxAge(1000*3600*24*7);//设置cookie的有效期
                 res.addCookie(cookie);//将cookie添加到响应中发送给客户端
             }
             res.sendRedirect("cookie/success.jsp");
         }else{
             res.sendRedirect("cookie/login.jsp?error=true");
         }
     }
 }

　　web.xml

<?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_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>javaweb06</display-name>
  <servlet>
      <servlet-name>loginservlet</servlet-name>
      <servlet-class>com.control.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>loginservlet</servlet-name>
      <url-pattern>/login</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>

　　实例2：继承HttpServlet类 +  web.xml注册

　　LoginServlet2.java

package com.control;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class LoginServlet2 extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //session
        HttpSession session = req.getSession();
        //application
        ServletContext app = getServletContext();

    }
}

　　web.xml文件同上，只不过将

<servlet-class>com.control.LoginServlet</servlet-class>

　　改为

<servlet-class>com.control.LoginServlet2</servlet-class>

　　实例3：继承HttpServlet类 + @WebServlet注解注册，不需要在web.xml文件中注册　　　
　　　LoginServlet3.java

package com.control;

import java.io.IOException;

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

@WebServlet("/login3")//此注解代替web.xml的配置文件
public class LoginServlet3 extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //session
        HttpSession session = req.getSession();
        //application
        ServletContext app = getServletContext();

    }
}