**

**
login.html文件

    
    


    

    姓名：
    登录
    
    


    

    姓名：
    密码：
    登录
    

@WebServlet("/s2")注解必须要有

package com.example.servlet02;

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 java.io.IOException;

@WebServlet("/s2")
public class Servlet02 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //防止乱码
        req.setCharacterEncoding("utf-8");
        //请求参数名
        System.out.println(req.getParameter("name"));
    }
}

//请求转发到首页
req.getRequestDispatcher(“index.jsp”).forward(req, resp);

package com.example.servlet02;

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 java.io.IOException;


@WebServlet("/s3")
public class Servlet03 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        //接收参数
        String name = req.getParameter("name");
        String psw = req.getParameter("psw");
        //打印输出
        System.out.println("姓名 " + name + " 密码 " + psw);

        //请求转发到首页
        req.getRequestDispatcher("index.jsp").forward(req, resp);



    }
}

index.jsp

<%@ page import="java.util.List" %>
<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>



    



<%--    
<%= "Hello World!" %>--%>
<%--    
--%>
<%--    
--%>
<%--    Hello Servlet--%>

<%-- 可以通过java脚本段， 在jsp页面写Java代码。jsp是动态页面   --%>
    <%
        String name = request.getParameter("name");
        String psw = request.getParameter("psw");
        out.print(name);
    %>
    
欢迎登录

    <%
        //获取req作用域
        String userName = (String) request.getAttribute("useName");

        //浏览器打印
        out.print("姓名：" + userName);

        //获取集合
        List list = (List) request.getAttribute("list");
        out.print(list.get(0));
    %>

request作用域

package com.example.servlet02;

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 java.io.IOException;
import java.util.AbstractList;
import java.util.ArrayList;
import java.util.List;


@WebServlet("/s4")
public class Servlet04 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        System.out.println("Servlet04............");
        String name = "张三";
        String psw = "123456";
        //集合
        List list = new ArrayList<>();
        list.add("pdd");
        list.add("taobao");

        req.setAttribute("useName", name);
        req.setAttribute("password", psw);
        req.setAttribute("list", list);

        //请求转发到首页
        req.getRequestDispatcher("index.jsp").forward(req, resp);

    }
}

req.setAttribute(“useName”, name);
设置作用域： request.setAttribute(参数名，参数值）
获取作用域： request.getAttribute(参数名），不需要参数值
移除作用域：request.removeAttribute(参数名）
创建String类型的集合： List list = new ArrayList<>();

这是我刚刚学习和理解，希望能一起探讨！