第一步 我们先Mysql创建数据库，写数据

这两个是写数据库的软件。

 启动mysql对应的版本型号。

user表

判断存在（有没有login的数据库，有就删掉）即删除。

DROP DATABASE IF EXISTS login;

创建数据库，使用数据库

 #创建数据库
CREATE DATABASE login;
#使用数据库
use login;

创建一个表我们这定义叫user，给表增添3条数据

#创建表
CREATE TABLE user(
    uid int PRIMARY KEY AUTO_INCREMENT,
    uname VARCHAR(32),
    passWord VARCHAR(32),
    phone VARCHAR(11),
    address VARCHAR(64)
);

INSERT INTO user(uname,password,phone,address) VALUES('张三','666','18965423548','南阳');
INSERT INTO user(uname,password,phone,address) VALUES('李四','333','18754263548','许昌');
INSERT INTO user(uname,password,phone,address) VALUES('小美','123','18565234759','信阳');
 

 4.查询表

SELECT * FROM user;

goods表

创建另一个表叫Goods，给表增添3条数据

create table goods(
    gid int PRIMARY KEY AUTO_INCREMENT,
    gname VARCHAR(32),
    price DOUBLE,
    mark VARCHAR(128)
);

INSERT INTO goods(gname,price,mark) VALUES('泡面',4.5,'够香够辣就是这个味！');
INSERT INTO goods(gname,price,mark) VALUES('火腿',8.5,'肉质细腻Q弹！');
INSERT INTO goods(gname,price,mark) VALUES('雪碧',3.5,'清爽冰凉随心爽！');

  2.查询表

select * from goods;

整体代码如下： 

#判断存在即删除DROP DATABASE IF EXISTS login;#创建数据库CREATE DATABASE login;#使用数据库use login;#创建表CREATE TABLE user(uid int PRIMARY KEY AUTO_INCREMENT,uname VARCHAR(32),password VARCHAR(32),phone VARCHAR(11),address VARCHAR(64));INSERT INTO user(uname,password,phone,address) VALUES('张三','666','18965423548','南阳');INSERT INTO user(uname,password,phone,address) VALUES('李四','333','18754263548','许昌');INSERT INTO user(uname,password,phone,address) VALUES('小美','123','18565234759','信阳');SELECT * FROM user WHERE uname = ? AND password = ?;SELECT * FROM user;create table goods(gid int PRIMARY KEY AUTO_INCREMENT,gname VARCHAR(32),price DOUBLE,mark VARCHAR(128));INSERT INTO goods(gname,price,mark) VALUES('泡面',4.5,'够香够辣就是这个味！');INSERT INTO goods(gname,price,mark) VALUES('火腿',8.5,'肉质细腻Q弹！');INSERT INTO goods(gname,price,mark) VALUES('雪碧',3.5,'清爽冰凉随心爽！');select * from goods;

 效果如下：

第二步 在idea中写出这两个表对应的Java实体类 

Mysql的表名要跟Java类(首字母大写)的表名一样 

User类

package com.chen.bean;public class User {    private Integer id;    private String uname;    private String password;    private String phone;    private String address;    public User() {    }    public User(Integer id, String uname, String password, String phone, String address) {        this.id = id;        this.uname = uname;        this.password = password;        this.phone = phone;        this.address = address;    }    public Integer getId() {        return id;    }    public void setId(int id) {        this.id = id;    }    public String getUname() {        return uname;    }    public void setUname(String uname) {        this.uname = uname;    }    public String getPassword() {        return password;    }    public void setPassword(String password) {        this.password = password;    }    public String getPhone() {        return phone;    }    public void setPhone(String phone) {        this.phone = phone;    }    public String getAddress() {        return address;    }    public void setAddress(String address) {        this.address = address;    }    @Override    public String toString() {        return "User{" +                "id=" + id +                ", uname='" + uname + '\'' +                ", password='" + password + '\'' +                ", phone='" + phone + '\'' +                ", address='" + address + '\'' +                '}';    }}

Goods类

package com.chen.bean;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() {    }    @Override    public String toString() {        return "zhuye{" +                "gid=" + gid +                ", gname='" + gname + '\'' +                ", price=" + price +                ", mark='" + mark + '\'' +                '}';    }    public Integer getGid() {        return gid;    }    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;    }}

第三步   在WEB下的.jsp中写出 首页(index.jsp) ，登录失败页面(error.jsp) ，登录页面(https://blog.csdn.net/weixin_67224308/article/details/login.jsp)， 注册页面(Https://blog.csdn.net/weixin_67224308/article/details/reGISter.jsp)，主页(zhuye.jsp)，添加页面（https://blog.csdn.net/weixin_67224308/article/details/addGoods.jsp），修改页面（showGoods）。

首页

<%--  Created by IntelliJ IDEA.  User: chenge  Date: 2023/2/13  Time: 19:09  To change this template use File | Settings | File Templates.--%><%@ page contentType="text/html;charset=UTF-8" language="java" %>  
登录注册

 2.登录页面

<%--  Created by IntelliJ IDEA.  User: chenge  Date: 2023/2/14  Time: 10:35  To change this template use File | Settings | File Templates.--%><%@ page contentType="text/html;charset=UTF-8" language="java" %>        
        账号:
        密码:
                   没有账号?请注册    

 3.登录失败页面

<%--  Created by IntelliJ IDEA.  User: chenge  Date: 2023/2/17  Time: 19:58  To change this template use File | Settings | File Templates.--%><%@ page contentType="text/html;charset=UTF-8" language="java" %>    
出错啦
返回登录

 4.注册页面

<%--  Created by IntelliJ IDEA.  User: chenge  Date: 2023/2/14  Time: 10:35  To change this template use File | Settings | File Templates.--%><%@ page contentType="text/html;charset=UTF-8" language="java" %>    
    账号:
    密码:
    手机号:
    地址:
    确认密码:
           已有账号?请登录

 5.登录成功进入的主页面

由后台数据库传递过来的商品数据。

<%

之间可以写服务器端代码

%>

<%=%>获取后台的变量值

   session在网络应用中称为“会话控制”，是服务器为了保存用户状态而创建的一个特殊的对象。简而言之，session就是一个对象，用于存储信息。 

<%--  Created by IntelliJ IDEA.  User: chenge  Date: 2023/2/17  Time: 19:35  To change this template use File | Settings | File Templates.--%><%@taglib prefix="a" uri="http://java.sun.com/jsp/jstl/core" %><%@ page contentType="text/html;charset=UTF-8" language="java" %>    
欢迎来自${user.address}的${user.uname}访问项目主页
        
添加商品        
    
    
        
商品编号
        
商品名称
        
商品价格
        
商品说明
    
    
    
        
            
${goods.gid}
            
${goods.gname}
            
${goods.price}
            
${goods.mark}
            
                修改                删除            
        
        

添加页面

<%--  Created by IntelliJ IDEA.  User: chenge  Date: 2023/2/25  Time: 13:36  To change this template use File | Settings | File Templates.--%><%@ page contentType="text/html;charset=UTF-8" language="java" %>    
    商品名称:
    商品价格:
    商品说明:
    

修改页面

 

<%--  Created by IntelliJ IDEA.  User: chenge  Date: 2023/2/27  Time: 8:27  To change this template use File | Settings | File Templates.--%><%@ page contentType="text/html;charset=UTF-8" language="java" %>    
商品修改
    商品编号:
    商品名称:
    商品价格:
    商品说明:
    

 第四步 JDBC操作层面

在src里建三个包  Dao，httpServlet，Util

 2.在Dao中先创建两个接口 这里起名叫UserDao，GoodsDao

UserDao

login登录页面有两个参数

register 返回一个user对象

package com.chen.Dao;import com.chen.bean.User;public interface UserDao {        User login(String uname,String password);        int register(User user);}

 GoodsDao

这里我们写方法，在impl里GoodsDaoImpl中调用方法。

package com.chen.Dao;import com.chen.bean.Goods;import java.util.List;public interface GoodsDao {    //全查    public List slectAll();    public Goods selectById(int gid);    //增    public int selectInsert(Goods goods);    //删    public int selectDelete(int gid);    //改    public int selectUpdate(Goods goods);}

再在Dao.impl中创建UserDaoImpl类，用这个类去继承UserDao接口，这里面写登录、注册JDBC的操作，用了分层操作，JDBC驱动、连接、调用方法、关闭资源 都在Util包中，httpservlet里写。

        util包-JDBCUtil类

package com.chen.Util;import com.chen.bean.User;import java.security.PublicKey;import java.sql.*;public class JDBCUtil {    private static String driver = "com.mysql.cj.jdbc.Driver";    private static String url = "jdbc:mysql://127.0.0.1:3306/login?useSSL=false&serverTimezone=UTC";    private static String user = "root";    private static String password = "root";    private static Connection conn = null;    public static Connection getCon() {        try {            //1.加载数据库驱动            Class.forName(driver);            //2.获取数据库连接            conn = DriverManager.getConnection(url, user, password);        } catch (Exception e) {            e.printStackTrace();        }        return conn;    }    //JDBCUtil.getCon()方法    public static void main(String[] args) {        System.out.println(JDBCUtil.getCon());    }    //登录的关闭资源    public static void close(ResultSet rs,PreparedStatement pstm,Connection conn) {        try {            if (rs!=null){                rs.close();            }            if (pstm!=null){                pstm.close();            }            if (conn!=null){                conn.close();            }        }catch (Exception e){            e.printStackTrace();        }    }    //注册的关闭资源    public static void close(PreparedStatement pstm, Connection conn) {        try {            if (pstm!=null){                pstm.close();            }            if (conn!=null){                conn.close();            }        }catch (Exception e){            e.printStackTrace();        }    }}

 UserDaoImpl

package com.chen.Dao.imlp;import com.chen.Dao.UserDao;import com.chen.Util.JDBCUtil;import com.chen.bean.User;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;public class UserDaoImpl implements UserDao {    User login = null;    Connection conn = null;  //数据库连接对象    PreparedStatement pstm = null;  //预处理对象    ResultSet rs = null;  //结果集对象    int i = 0;    //登录    public User login (String uname, String password){        try{            conn = JDBCUtil.getCon();            //3.sql语句            String sql = "select * from user where uname=? and password=?";            //4.获取预处理对象            pstm = conn.prepareStatement(sql);            //5.传参            pstm.setObject(1,uname);            pstm.setObject(2,password);            //6.执行查询            rs = pstm.executeQuery();            //7.解析结果集            if (rs.next()){                login = new User();                //从结果集中获取数据，封装到实体类对象中                int uid = rs.getInt("uid");                login.setId(uid);                login.setUname(rs.getString("uname"));                login.setPassword(rs.getString("password"));                login.setPhone(rs.getString("phone"));                login.setAddress(rs.getString("address"));            }        } catch (Exception throwables) {            throwables.printStackTrace();        }finally {            //8.关闭资源            JDBCUtil.close(rs,pstm,conn);        }        return login;    }    @Override    //注册    public int register(User user) {        try {            conn = JDBCUtil.getCon();            String sql = "insert into user(uname,password,phone,address) values(?,?,?,?)";            pstm = conn.prepareStatement(sql);            pstm.setObject(1,user.getUname());            pstm.setObject(2,user.getPassword());            pstm.setObject(3,user.getPhone());            pstm.setObject(4,user.getAddress());            i = pstm.executeUpdate();        } catch (Exception e) {            e.printStackTrace();        }finally {            JDBCUtil.close(pstm,conn);        }        return i;    }}

 GoodsDaoImpl

在这里面就要完成全查的操作、添加操作、删除操作、修改操作根据id查找那条数据展现在页面中，再去写sql的修改代码操作。

package com.chen.Dao.imlp;import com.chen.Dao.GoodsDao;import com.chen.Util.JDBCUtil;import com.chen.bean.Goods;import com.chen.bean.User;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.util.ArrayList;import java.util.List;public class GoodsDaoImpl implements GoodsDao {    private User login = null;    private Connection conn = null;  //数据库连接对象    private PreparedStatement pstm = null;  //预处理对象    private ResultSet rs = null;  //结果集对象    private int i = 0; //增删改受影响的行数//全查    @Override    public List slectAll() {        List goodslist = new ArrayList<>();        try {            conn = JDBCUtil.getCon();            //3.sql语句            String sql = "select * from goods";            //4.获取预处理对象            pstm = conn.prepareStatement(sql);            //5.执行查询            rs = pstm.executeQuery();            Goods goods=null;            //6.解析结果集            while (rs.next()){                goods = new Goods();                goods.setGid(rs.getInt("gid"));                goods.setGname(rs.getString("gname"));                goods.setPrice(rs.getDouble("price"));                goods.setMark(rs.getString("mark"));                goodslist.add(goods);            }        }catch (Exception e){            e.printStackTrace();        }finally {            try {                if (rs!=null){                    rs.close();                }                if (pstm!=null){                    pstm.close();                }                if (conn!=null){                    conn.close();                }            }catch (Exception e){                e.printStackTrace();            }        }        return goodslist;}//模糊查询  public List seach(String keyword) {        List goodslist = new ArrayList<>();        try {            conn = JDBCUtil.getCon();            //3.sql语句            String sql = "select * from goods where gname like concat('%',?,'%')";            //4.获取预处理对象            pstm = conn.prepareStatement(sql);            pstm.setObject(1,keyword);            //5.执行查询            rs = pstm.executeQuery();            //6.解析结果集            while (rs.next()){                goods = new Goods();                goods.setGid(rs.getInt("gid"));                goods.setGname(rs.getString("gname"));                goods.setPrice(rs.getDouble("price"));                goods.setMark(rs.getString("mark"));                goodslist.add(goods);            }        }catch (Exception e){            e.printStackTrace();        }finally {            try {                if (rs!=null){                    rs.close();                }                if (pstm!=null){                    pstm.close();                }                if (conn!=null){                    conn.close();                }            }catch (Exception e){                e.printStackTrace();            }        }        return goodslist;    }//id查询 public Goods selectById(int gid){        Goods goods = null;        try {            conn = JDBCUtil.getCon();            //3.sql语句            String sql = "select * from goods where gid=?";            //4.获取预处理对象            pstm = conn.prepareStatement(sql);            pstm.setObject(1,gid);            //5.执行查询            rs = pstm.executeQuery();            //6.解析结果集            if (rs.next()){                goods = new Goods();                goods.setGid(rs.getInt("gid"));                goods.setGname(rs.getString("gname"));                goods.setPrice(rs.getDouble("price"));                goods.setMark(rs.getString("mark"));            }        }catch (Exception e){            e.printStackTrace();        }finally {            try {                if (rs!=null){                    rs.close();                }                if (pstm!=null){                    pstm.close();                }                if (conn!=null){                    conn.close();                }            }catch (Exception e){                e.printStackTrace();            }        }        return goods;    }//添加数据    @Override    public int selectInsert(Goods goods) {            try {                conn = JDBCUtil.getCon();                //3.sql语句                String sql = "insert into goods(gname,price,mark) values (?,?,?)";                //4.获取预处理对象                pstm = conn.prepareStatement(sql);                pstm.setObject(1,goods.getGname());                pstm.setObject(2,goods.getPrice());                pstm.setObject(3,goods.getMark());                //5.执行查询                i = pstm.executeUpdate();            }catch (Exception e){                e.printStackTrace();            }finally {                try {                    if (pstm!=null){                        pstm.close();                    }                    if (conn!=null){                        conn.close();                    }                }catch (Exception e){                    e.printStackTrace();                }            }            return i;    }//删除    @Override    public int selectDelete(int gid) {        System.out.println("selectDelete");            try {                conn = JDBCUtil.getCon();                //3.sql语句                String sql = "delete  from goods where gid=?";                //4.获取预处理对象                pstm = conn.prepareStatement(sql);                pstm.setObject(1,gid);                //5.执行查询                i = pstm.executeUpdate();            }catch (Exception e){                e.printStackTrace();            }finally {                try {                    if (pstm!=null){                        pstm.close();                    }                    if (conn!=null){                        conn.close();                    }                }catch (Exception e){                    e.printStackTrace();                }            }            return i;    }//修改    @Override    public int selectUpdate(Goods goods) {        try {            conn = JDBCUtil.getCon();            //3.sql语句            String sql = "update goods set gname=?,price=?,mark=? where gid=?";            //4.获取预处理对象            pstm = conn.prepareStatement(sql);            pstm.setObject(1,goods.getGname());            pstm.setObject(2,goods.getPrice());            pstm.setObject(3,goods.getMark());            pstm.setObject(4,goods.getGid());            //5.执行查询            i = pstm.executeUpdate();            System.out.println("i="+i);        }catch (Exception e){            e.printStackTrace();        }finally {            try {                if (pstm!=null){                    pstm.close();                }                if (conn!=null){                    conn.close();                }            }catch (Exception e){                e.printStackTrace();            }        }        return i;    }}

 第五步 业务处理层面

httpServlet中写的三个类是处理 ：

1.设置请求和响应的编码格式2.获取请求的参数3.执行业务处理

Login

映射地址

@WebServlet("/login")

请求：

request.getRequestDispatcher("        ").forward(request,response);//请求别的地址

package com.chen.httpServlet;import com.chen.Dao.UserDao;import com.chen.Dao.imlp.UserDaoImpl;import com.chen.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 {    @Override    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        System.out.println("Login-get");        doPost(request,response);    }    @Override    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        System.out.println("Login-post");        //前端请求（request），后端处理后，最后给前端做出响应（response）        //1.设置请求和响应的编码格式，以及响应的格式        request.setCharacterEncoding("utf-8");  //设置请求的编码格式为中文        response.setCharacterEncoding("utf-8");    //设置响应的编码格式        response.setContentType("text/html;charset=UTF-8");  //以什么样的格式 （文本/网页）响应        //2.获取请求的参数        String uname = request.getParameter("uname"); //根据表单的name属性获取用户输入的值        String password = request.getParameter("password");        //3.执行业务处理        UserDao userDao = new UserDaoImpl();        User login = userDao.login(uname,password);        //判断登录的用户信息是否为空        if (login!=null) {            System.out.println("登录成功！");            //登录成功,当前servlet的业务处理完毕----后续执行查询商品的操作应该由别人来完成---请求转发给别的servlet处理            request.getRequestDispatcher("selectAllGoods").forward(request,response);//请求别的地址        } else {            //登录失败，跳转到错误页            response.sendRedirect("error.jsp");        }    }}

 Register

映射地址

@WebServlet("/register")

package com.chen.httpServlet;import com.chen.Dao.UserDao;import com.chen.Dao.imlp.UserDaoImpl;import com.chen.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;import java.sql.*;@WebServlet("/register")public class Register extends HttpServlet {    @Override    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        System.out.println("register-get");        doPost(request,response);    }    @Override    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        System.out.println("register-post");        //1.设置请求和响应的编码格式，以及响应的格式        request.setCharacterEncoding("utf-8");  //设置请求的编码格式为中文        response.setCharacterEncoding("utf-8");    //设置响应的编码格式        //2.获取请求的参数        String uname = request.getParameter("uname"); //根据表单的name属性获取用户输入的值        String password = request.getParameter("password");        String phone = request.getParameter("phone");        String address = request.getParameter("address");        //封装：把上面所有的变量装载到User对象中        User user = new User();        user.setUname(uname);        user.setPassword(password);        user.setPhone(phone);        user.setAddress(address);        System.out.println(user);        //3.执行业务处理        UserDao userDao = new UserDaoImpl();        int i = userDao.register(user);        //判断登录的用户信息是否为空        if (i > 0) {            //注册成功，跳转到登录页面            response.sendRedirect("https://blog.csdn.net/weixin_67224308/article/details/login.jsp");//指定跳转的页面        } else {            //登录失败，跳转到错误页            response.sendRedirect("https://blog.csdn.net/weixin_67224308/article/details/register.jsp");        }    }}

 SelectAllGoods

映射地址

@WebServlet("/selectAllGoods")

//通过request获取session对象，该对象可以向前端传递传输数据的容器HttpSession               session = req.getSession();

package com.chen.httpServlet;import com.chen.Dao.imlp.GoodsDaoImpl;import com.chen.bean.Goods;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;import java.io.IOException;import java.util.List;@WebServlet("/selectAllGoods")public class SelectAllGoods extends HttpServlet {    @Override    protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        doPost(req, resp);    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        System.out.println("SelectAllGoods..dopost");        //查询所有商品信息        GoodsDaoImpl goodsDao = new GoodsDaoImpl();        List goodsList = goodsDao.slectAll();        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递传输数据的容器        HttpSession session = req.getSession();        //向session 中存入商品信息集合        session.setAttribute("goodsList", goodsList);        //登录成功，跳转到主页        resp.sendRedirect("zhuye.jsp");//指定的跳转页面    }}

InsertGoods

映射地址

@WebServlet("/addGoods")

package com.chen.httpServlet;import com.chen.Dao.GoodsDao;import com.chen.Dao.imlp.GoodsDaoImpl;import com.chen.bean.Goods;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("/addGoods")public class InsertGoods 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 {        req.setCharacterEncoding("UTF-8");        resp.setCharacterEncoding("UTF-8");        //获取请求参数并封装到Goods对象中        Goods goods = new Goods();        goods.setGname(req.getParameter("gname"));        //使用Double包装类把req.getParameter获取到字符串数字 转换为 double类型的数据        goods.setPrice(Double.parseDouble(req.getParameter("price")));        goods.setMark(req.getParameter("mark"));        //执行JDBC的添加操作        GoodsDao goodsDao = new GoodsDaoImpl();        int i = goodsDao.selectInsert(goods);        if (i > 0) {            //添加成功            req.getRequestDispatcher("selectAllGoods").forward(req, resp);        } else {            //添加失败            req.setAttribute("error_msg", "添加商品出错了!");            req.getRequestDispatcher("error.jsp").forward(req, resp);        }    }}

 DeleteGoods

映射地址

@WebServlet("/del")

package com.chen.httpServlet;import com.chen.Dao.GoodsDao;import com.chen.Dao.imlp.GoodsDaoImpl;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("/del")public class DeleteGoods 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 {        int gid = Integer.parseInt(req.getParameter("gid"));        //根据id执行数据库的删除        GoodsDao goodsDao = new GoodsDaoImpl();        int i = goodsDao.selectDelete(gid);        if (i>0){            //请求转发，查讯所有商品信息（刷新）            req.getRequestDispatcher("selectAllGoods").forward(req,resp);        }else {            req.setAttribute("error_msg","删除出现了问题!");            req.getRequestDispatcher("error.jsp").forward(req,resp);        }    }}

FindByIdGoods 

映射地址

@WebServlet("/findById")

package com.chen.httpServlet;import com.chen.Dao.GoodsDao;import com.chen.Dao.imlp.GoodsDaoImpl;import com.chen.bean.Goods;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("/findById")public class FindByIdGoods 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 {        int gid = Integer.parseInt(req.getParameter("gid"));        //根据gid查询商品信息        GoodsDao goodsDao = new GoodsDaoImpl();        Goods goods = goodsDao.selectById(gid);        if (goods!= null){            //把数据存储到req域对象中，然后请求转发到页面            req.setAttribute("goods",goods);            req.getRequestDispatcher("showGoods.jsp").forward(req,resp);        }else {            //登录失败，跳转到错误页            req.setAttribute("error_msg","修改出现异常!");            req.getRequestDispatcher("error.jsp").forward(req,resp);        }    }}

UpdateGoods

映射地址

@WebServlet("/updateGoods")

package com.chen.httpServlet;import com.chen.Dao.GoodsDao;import com.chen.Dao.UserDao;import com.chen.Dao.imlp.GoodsDaoImpl;import com.chen.Dao.imlp.UserDaoImpl;import com.chen.bean.Goods;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("/updateGoods")public class UpdateGoods 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 {        req.setCharacterEncoding("utf-8");        resp.setCharacterEncoding("utf-8");        //获取表单请求的数据，封装到goods对象中        Goods goods = new Goods();        goods.setGid(Integer.parseInt(req.getParameter("gid")));        goods.setGname(req.getParameter("gname"));        goods.setPrice(Double.parseDouble(req.getParameter("price")));        goods.setMark(req.getParameter("mark"));        //执行数据库的修改操作       GoodsDao goodsDao = new GoodsDaoImpl();        goodsDao.selectUpdate(goods)        if (i>0){            //请求转发，查讯所有商品信息（刷新）            req.getRequestDispatcher("selectAllGoods").forward(req,resp);        }else {            req.setAttribute("error_msg","修改失败，请重新尝试!");            req.getRequestDispatcher("error.jsp").forward(req,resp);        }    }}

Seach

@WebServlet("/seach")

package com.chen.httpServlet;import com.chen.Dao.GoodsDao;import com.chen.Dao.imlp.GoodsDaoImpl;import com.chen.bean.Goods;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;import java.io.IOException;import java.util.List;@WebServlet("/seach")public class Seach 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 {        req.setCharacterEncoding("utf-8");        resp.setCharacterEncoding("utf-8");        String keyword = req.getParameter("keyword");        //根据关键词执行JDBC的模糊查询        GoodsDao goodsDao = new GoodsDaoImpl();        List goodsList = goodsDao.seach(keyword);        //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递传输数据的容器        HttpSession session = req.getSession();        //向session 中存入商品信息集合        session.setAttribute("goodsList", goodsList);        //登录成功，跳转到主页        resp.sendRedirect("zhuye.jsp");//指定的跳转页面    }}

到这里代码就结束了，数据库原本的三条数据，正确的账号密码。

如果注册，注册的信息就存在后台的数据库里，如果注册成功就可以登录成功,在后台数据库里添加商品信息，通过session在主页页面中就能看到商品信息。增删改查操作。

不能随意访问网址就能进入注册、添加、主页页面中，所以我们要写个过滤器，防止外来人员直接访问。

第六步 Filter过滤器

1、filter简介

Filter中文意思为过滤器。顾名思义，过滤器可在浏览器以及目标资源之间起到一个过滤的作用。例如:水净化器，可以看成是生活中的一个过滤器，他可以将污水中的杂质过滤，从而使进入的污水变成净水。对于WEB应用来说，过滤器是一个驻留在服务器中的WEB组件，他可以截取客户端和WEB资源之间的请求和响应信息。WEB资源可能包括ServletJSPHTML页面等。

Filter是Tomcat容器内的过滤器，在请求到达容器是先会调用过滤器，再调用我们的servlet或者jsp。

当服务器收到特定的请求后，会先将请求交给过滤器，程序员可以在过滤器中对请求信息进行读取修改等操作，然后将请求信息再发送给目标资源。目标资源作出响应后，服务器会再次将响应转交给过滤器，在过滤器中同样可以对响应信息做一些操作，然后再将响应发送给浏览器。

也就是说过滤器可以在WEB资源收到请求之前，浏览器收到响应之前，对请求和响应信息做一些相应的操作。

在一个WEB应用中可以部署多个过滤器，多个过滤器就组成了一个过滤器链，请求和响应必须在经过多个过滤器后才能到达目标。

过滤器不是必须将请求传送到下一个过滤器(或WEB资源)，也可以自己来处理请求，发送响应。

2、filter的实现

 Filter接口，实现Filter需要实现该接口
1、init()方法用于初始化Filter。

doFilter()作用和service()方法类似，是过滤请求和响应的主要方法。

destroy0用于在Filter对象被销毁前做一些收尾工作。如:释放资源等

3、filter的生命周期

Filter的生命周期和Servlet类似
构造器:创建Filter实例是调用，Filter实例服务器一旦启动就会被创建
init():实例创建后马上被调用，用来对Filter做一些初始化的操作
doFilter():Filter的主要方法，用来完成过滤器主要功能的方法，每次访问目标资源时都会调用。
destroy():服务器停止时调用，用来释放资源

首先

映射所有

@WebFilter("/*")

实现filter接口

 

 因为要登录（+登录的映射地址），没有账号的要注册（+注册的映射地址），登陆失败跳转错误页面，这些页面都需要放行，直接访问主页会回到登录页面。

具体代码如下：

package com.chen.filter;import com.chen.bean.User;import javax.servlet.*;import javax.servlet.annotation.WebFilter;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import java.io.IOException;@WebFilter("/*")public class MyFilter implements Filter {    @Override    public void init(FilterConfig filterConfig) throws ServletException {        System.out.println("初始化..");    }    @Override    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {        //1.在过滤器中把servletRequest、servletResponse转换为HttpServletRequest、HttpServletResponse        HttpServletRequest request = (HttpServletRequest) servletRequest;        HttpServletResponse response = (HttpServletResponse) servletResponse;        //2.获取请求的资源路径        String servletPath = request.getServletPath();        //3.获取session储存的用户对象        HttpSession session = request.getSession();        User user = (User) session.getAttribute("user");        //4.1如果请求index.jsp、https://blog.csdn.net/weixin_67224308/article/details/login.jsp、login、https://blog.csdn.net/weixin_67224308/article/details/register.jsp、register、error.jsp则放行        if (servletPath.equals("/index.jsp") ||servletPath.equals("/https://blog.csdn.net/weixin_67224308/article/details/login.jsp") ||servletPath.equals("/login") ||servletPath.equals("/https://blog.csdn.net/weixin_67224308/article/details/register.jsp") ||servletPath.equals("/register") ||servletPath.equals("/error.jsp")){            filterChain.doFilter(servletRequest,servletResponse);//放行        }else if (user!=null){            filterChain.doFilter(servletRequest,servletResponse);//放行        }else {            response.sendRedirect("https://blog.csdn.net/weixin_67224308/article/details/login.jsp");        }    }    @Override    public void destroy() {        System.out.println("销毁..");    }}

项目效果如下： 

来源地址：https://blog.csdn.net/weixin_67224308/article/details/129114921