用户登录成功后跳转到主页并展示数据库的商品信息；以及1.后端在作用域对象中存储数据；2.在页面中使用EL表达式取出数据；3.可以使用JSTL标签进行集合元素的遍历

数据库信息：

 一、创建一个bean包 里面创建一个实体类

Goods类：

package com.nai.bean;

public class Goods {
    private Integer gid;
    private String gname;
    private Double price;
    private String mark;
    public Goods(Integer gid, String gname, Double price, String mark) {
        this.gid = gid;
        this.gname = gname;
        this.price = price;
        this.mark = mark;
    }
    public Goods() {
    }
    public Integer getGid() {
        return gid;
    }
    @Override
    public String toString() {
        return "Goods{" +
                "gid=" + gid +
                ", gname='" + gname + '\'' +
                ", price='" + price + '\'' +
                ", mark='" + mark + '\'' +
                '}';
    }
    public void setGid(Integer gid) {
        this.gid = gid;
    }
    public String getGname() {
        return gname;
    }
    public void setGname(String gname) {
        this.gname = gname;
    }
    public Double getPrice() {
        return price;
    }
    public void setPrice(Double price) {
        this.price = price;
    }
    public String getMark() {
        return mark;
    }
    public void setMark(String mark) {
        this.mark = mark;
    }
}

 第二步：创建一个Dao包 里面创建一个GoodsDaoImpl类

 

 GoodsDaoImpl类：

package com.nai.Dao.impl;

import com.nai.bean.Goods;
import com.nai.bean.User;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class GoodsDaoImpl {
    private static String jdbcdirver = "com.mysql.cj.jdbc.Driver";
    private static String jdbcurl = "jdbc:mysql://localhost:3306/myweb?useSSL=false&serverTimezone=UTC";
    private static String jdbcuser = "root";
    private static String jdbcpassword = "root";

    Connection con = null;
    PreparedStatement pstm = null;
    ResultSet rs = null;
    User Fi = null;
    int row = 0;

    public List selectAll() {
        List goodsList = new ArrayList<>();

        try {
            Class.forName(jdbcdirver);
            con = DriverManager.getConnection(jdbcurl, jdbcuser, jdbcpassword);
            String sql = "select * from t_goods";
            pstm = con.prepareStatement(sql);
            rs = pstm.executeQuery();
            while (rs.next()) {
                //从结果集中获取数据，封装到Goods对象中
                Goods goods = new Goods();
                goods.setGid(rs.getInt("gid"));
                goods.setGname(rs.getString("gname"));
                goods.setPrice(rs.getDouble("price"));
                goods.setMark(rs.getString("mark"));
                //把当前行对应的对象存储到集合中
                goodsList.add(goods);
            }
        } catch (Exception e) {

            e.printStackTrace();
        } finally {
            try {
                if (rs != null) {
                    rs.close();
                }
                if (pstm != null) {
                    pstm.close();
                }
                if (con != null) {
                    con.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }

        }
        return goodsList;
    }
}

 第三步：创建一个servlet包  里面创建两个类

Login（登录）类：

package com.nai.servlet;

import com.nai.Dao.UserDao;
import com.nai.Dao.impl.UserDaoImpl;
import com.nai.bean.User;


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("/Login")
public class Login extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("Login-get...");
        doPost(request, response);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置请求和响应的编码格式，以及响应的格式
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charest=UTF-8");
        //获取请求的参数
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        //执行业务处理---jdbc的操作
        UserDaoImpl userDao= new UserDaoImpl();
        User Fi=userDao.login(username,password);
        //判断登录的用户信息是否为空
        if(Fi!=null){
         req.getRequestDispatcher("selectAllGoods").forward(req,resp);
       }else {
           resp.sendRedirect("user.jsp");
       }
}
}

 1.后端在作用域对象中存储数据；

 

 2.在页面中使用EL表达式取出数据；3.可以使用JSTL标签进行集合元素的遍历

 

selectAllGoods类：

package com.nai.servlet;

import com.nai.Dao.impl.GoodsDaoImpl;
import com.nai.bean.Goods;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.util.List;

@WebServlet("/selectAllGoods")
public class servletAllGoods extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            doPost(request,response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //查询所有商品的信息
        GoodsDaoImpl goodsDao=new GoodsDaoImpl();
        List goodsList=goodsDao.selectAll();
        System.out.println(goodsList);
        //把数据传递到前端页面
        //通过request获取session对象，该对象可以向前端传输数据的容器
        HttpSession session =request.getSession();
        //向session中存入商品信息集合
        session.setAttribute("goodsList",goodsList);
        //登录成功，跳转到上面
        response.sendRedirect("goods.jsp");
    }
}

****** 

 第五步：创建一个until包 里面创建数据库与java连接的类

 

 JDBCUntil类：

package com.nai.until;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class JDBCUtil {
    private static  String jdbcdirver="com.mysql.cj.jdbc.Driver";
    private static  String jdbcurl="jdbc:mysql://localhost:3306/myweb?useSSL=false&serverTimezone=UTC";
    private static  String jdbcuser="root";
    private static  String jdbcpassword="root";
    private static  Connection connection=null;

    public static Connection getCon(){
        try {
            Class.forName(jdbcdirver);
            connection= DriverManager.getConnection(jdbcurl,jdbcuser,jdbcpassword);

        }catch (Exception e){
            e.printStackTrace();
        }
        return connection;
    }

    public  static void close(   PreparedStatement pstm, Connection con){
        try{

            if(pstm!=null){
                pstm.close();
            }
            if(con!=null){
                con.close();
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }
    public static Connection getCo(){
        try {
            Class.forName(jdbcdirver);
            connection= DriverManager.getConnection(jdbcurl,jdbcuser,jdbcpassword);

        }catch (Exception e){
            e.printStackTrace();
        }
        return connection;
    }

    public  static  void login(ResultSet rs, PreparedStatement pstm, Connection con){
        try{
            if(rs!=null){
                rs.close();
            }
            if(pstm!=null){
                pstm.close();
            }
            if(con!=null){
                con.close();
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

第六步：创建jsp文件 index.jsp、goods.jsp、login.jsp（后端跳转前端）

 index.jsp：

<%--
  Created by IntelliJ IDEA.
  User: Lenovo
  Date: 2023/2/14
  Time: 10:52
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


  


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 goods.jsp：

<%@ page import="java.util.List" %>
<%@ page import="com.nai.bean.Goods" %><%--
  Created by IntelliJ IDEA.
  User: Lenovo
  Date: 2023/2/16
  Time: 11:00
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


  


登录成功
欢迎来到javaweb商店

<%
//获取session
  HttpSession session1=request.getSession();
  //从session中取出数据
  List goodsList = (List) session1.getAttribute("goodsList");
  //遍历集合元素
  for(Goods goods : goodsList){
%>
    
    
    <%
  }
%>
  

  

  

  
商品编号
  
商品名称
  
商品价格
  
商品说明
  
  
  

      
<%=goods.getGid()%>
      
<%=goods.getGname()%>
      
<%=goods.getPrice()%>
      
<%=goods.getMark()%>
    

login.jsp：

<%--
  Created by IntelliJ IDEA.
  User: Lenovo
  Date: 2023/2/14
  Time: 11:00
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    



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 *****

最终效果图：