创建jsp页面，然后转发到servlet下，接受jsp页面传过来的值，拿着这些值去访问service服务层接口，服务层写个实类，这个实现类去服务层的接口，然后这个服务层的实现类再去访问dao层的接口，在持久层dao中在编写一个dao层接口的实现类去实现dao层的接口，最后在dao层的的实现类去访问数据库。

项目视频演示

学生管理系统项目演示

设置数据库studenttest

①、创建user表

其中包括设置删除的u_isdelete（0是存在，1是删除）

create table user(
u_name varchar(20),
u_id int primary key auto_increment,
 u_pwd varchar(20) ,
u_phone varchar(20) not null,
u_role  int not null,
u_isdelete int not null
)
charset=utf8;

创建项目

项目界面总览

jsp页面

登录界面login.jsp

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" %>
<%
    String path = request.getContextPath();
    String basepath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
%>
<html>
<head>
    <base href="<%=basepath %>"/>
    <meta charset="utf-8"/>
    <title>登录界面</title>
    <%--  css代码--%>
    <style>
        #fame_{
            width: 500px;
            height: 400px;
            margin-left: 600px;
            margin-top: 200px;
            background-color: aqua;
            /*边框黑色 实线 2像素*/
            border: black solid 2px;
        }
        #inner_{
            margin-left: 140px;
            margin-top: 160px;
        }
    </style>


</head>
<body>
<h1 align="center" style="color: red">登录界面</h1>
<div id="fame_"  >
    <div id="inner_">
        用户:<input type="text" id="u_id">
        <b>  <span id="span1" style="color: crimson">${error}</span></b><br><br>
        密码:<input type="password" id="u_pwd">
        <b>  <span id="span2" style="color: crimson"></span></b><br><br>
        <button id="btn01">重置</button>
        <button id="btn02" style="margin-left: 20px">登录</button><br>

        <script>
            <%-- 这里写js代码验证账号密码值是否为空--%>
              window.onload=function() {
                  document.getElementById("btn02").onclick = function () {
                      let id_value = document.getElementById("u_id").value
                      if (id_value == null || id_value == "") {
                          document.getElementById("span1").innerHTML = "用户名不能为空"
                          return;
                      }

                      //判断密码是否为空
                      let pwd = document.getElementById("u_pwd").value
                      if (pwd == null || pwd == "") {
                          document.getElementById("span2").innerHTML = "密码不能为空"
                          return;
                      }
                      //跳转到servlet
                      window.location.href = "login?u_id=" + id_value + "&u_pwd=" + pwd;
                  }
                  //在次点击清空错误信息
                  document.getElementById("u_id").onfocus = function () {
                      document.getElementById("span1").innerText = ""
                  }
                  document.getElementById("u_pwd").onfocus = function () {
                      document.getElementById("span2").innerText = ""
                  }
                  //清空内容
                  document.getElementById("btn01").onclick=function () {
                      document.getElementById("u_id").value="";
                      document.getElementById("u_pwd").value="";
                  }
              }
        </script>
    </div>
</div>
</body>
</html>

主界面mainPage.jsp

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" %>
<%
    String path = request.getContextPath();
    String basepath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
%>
<%--JSTL语法，可以使用user.getName()方法--%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>主界面</title>
    <style>
        #head_{
            height: 100px;
            width: 100%;
           background-color: darkcyan;
        }
        #personFile{
            width: 120px;
            height: 50px;
            padding-top: 25px;
            margin-left: 90%;
        }
        #search{
            height: 70px;
            width: 100%;
         background-color: aqua;
        }
        #inner_s{
            /*width: 200px;
            height: 40px;
            padding-right: 70%;
            padding-top: 50%;*/
            width: 30%;
            padding-top:25px;
            padding-left: 45%;
        }
        #table{
            margin-left: 30%;
            margin-top: 30px;
        }
        td{
            text-align: center;
            height: 20px;
            width: 150px;
            border:  darkcyan 2px solid;
            padding:6px;

        }


    </style>

</head>
<body>

<div id="head_">
   <h2>
       <div id="personFile" >
        名字:<span style="color: red">${user.getU_name()}</span><br>
        编号:<span style="color: red">${user.getU_id()}</span>
       </div>
   </h2>
</div>


<div id="search">
    <div id="inner_s">
        <input type="text" style="font-size: 20px; height: 26px;width: 190px " id="fileId">&nbsp;&nbsp;
        <button  style="font-size: 18px; height: 28px;"  id="cx"margin-left: 30px>查询</button>
        <button  style="font-size: 18px; height: 28px;" id="addUser" margin-left: 100px>添加</button>
        <button  style="font-size: 18px; height: 28px;" id="deleteUser">删除</button>
        <button  style="font-size: 18px; height: 28px;" id="changeUser">修改</button>
       <b> <span style="color: crimson">${tip}</span></b>
    </div>
</div>
<script>
           //提交
    document.getElementById("cx").onclick=function(){
        let v = document.getElementById('fileId').value;
        //访问服务器searchServlet
        window.location.href = "searchServlet?v=" + v+"&id=${user.getU_name()}";
    }
    //删除
    document.getElementById("deleteUser").onclick=function () {
       let v =document.getElementById('fileId').value;

        window.location.href = "deleteServlet?v="+v+"&id=${user.getU_name()}";
    }
     // 添加跳转到AddUser.jsp界面
    document.getElementById("addUser").onclick=function () {
        window.location = "AddUser.jsp";
    }
         //修改，跳转到change.jsp
           document.getElementById("changeUser").onclick=function () {
               let v =document.getElementById('fileId').value;
               window.location.href = "change.jsp";
           }
</script>

<div>
    <table id="table" style="height: 30px;width: 700px;border: black 1px solid;border-collapse:collapse;">

       <tr style="font-weight: bold" >
            <td>学生id</td>
            <td>学生名字</td>
            <td>学生电话</td>
            <td>学生成绩</td>
            <td>学生品行</td>
        </tr>
      <%--jstl语法遍历,var是一个指指针--%>
        <c:forEach items="${arr}" var="item">
            <tr>
                <td>${item.getU_id()}</td>
                <td>${item.getU_name()}</td>
                <td>${item.getU_phone()}</td>
                <td style="color: deeppink"> 优秀</td>
                <td style="color: red">良好</td>
                </td>
            </tr>

        </c:forEach>

    </table>
</div>


<div>

</div>



</body>
</html>

添加学生信息AddUser.jsp

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" %>
<%
    String path = request.getContextPath();
    String basepath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <base href="<%=basepath %>"/>
    <meta charset="utf-8"/>
    <title>添加信息界面</title>
</head>
<style>
    #div1{
        width: 400px;
        height: 300px;
        margin-left: 600px;
        margin-top: 200px;
      background-color:deepskyblue;
        /*边框黑色 实线 2像素*/
        border: black solid 2px;
    }

</style>
<body>
<h2 align="center" >添加学生信息</h2><br><br>
<div id="div1" >

     <tr> 学生id:<input type="text" id="u_id" >
       <span id="span01" style="color: red"></span> <br><br></tr>
       <tr>  姓名:<input type="text" id="u_name" ><br><br></tr>
       <tr>  密码:<input type="password" id="u_pwd"><br><br></tr>
       <tr> 电话号码:<input type="text" id="u_phone"><br><br></tr>


<button id="btn3">提交</button>
    <script>
        document.getElementById("btn3").onclick=function(){
            //获取填写的数据
           let u_id=document.getElementById("u_id").value;
            let u_name=document.getElementById("u_name").value;
            let u_pwd=document.getElementById("u_pwd").value;
            let u_phone=document.getElementById("u_phone").value;

           if(u_id==null||u_id==""||u_name==null||u_name==""){
               document.getElementById("span01").innerText="id或名字为为空"
           }else{
               //把数据发送到后端，发送到servlet的addUser路径下
           window.location.href="addUser?u_id="+u_id+"&u_pwd="+u_pwd+"&u_name="+u_name+"&u_phone="+u_phone+"&id=${user.getU_name()}";
           }
        }
        document.getElementById("u_id").onfocus=function () {
            document.getElementById("span01").innerText=""
        }

    </script>
</div>
</body>
</html>

修改学生信息change.jsp

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" %>
<%
    String path = request.getContextPath();
    String basepath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
%>
<html>
<head>
    <base href="<%=basepath %>"/>
    <meta charset="utf-8"/>
    <title>修改界面</title>
</head>

<style>
    #div1{
        width: 400px;
        height: 300px;
        margin-left: 600px;
        margin-top: 200px;
        background-color:deepskyblue;
        /*边框黑色 实线 2像素*/
        border: black solid 2px;
    }

</style>
<body>
<h2 align="center" >修改学生信息</h2><br><br>
<div id="div1" >

     修改的学生id:<input type="text" id="u_id" >
        <span id="span01" style="color: red"></span> <br><br>
   姓名:<input type="text" id="u_name" ><br><br>
      密码:<input type="password" id="u_pwd"><br><br>
     电话号码:<input type="text" id="u_phone"><br><br>


    <button id="btn3">提交</button>
    <script>
        //获取填写数据
        document.getElementById("btn3").onclick=function(){
            let u_id=document.getElementById("u_id").value;
            let u_name=document.getElementById("u_name").value;
            let u_pwd=document.getElementById("u_pwd").value;
            let u_phone=document.getElementById("u_phone").value;
          //判断非空
            if(u_id==null||u_id==""||u_name==null||u_name==""){
                document.getElementById("span01").innerText="id或名字为为空"
            }else{
                //不为空就转发到后端
                window.location.href="changeUser?u_id="+u_id+"&u_pwd="+u_pwd+"&u_name="+u_name+"&u_phone="+u_phone+"&id=${user.getU_name()}";
            }
        }
        //再次点击清除错误信息提示
        document.getElementById("u_id").onfocus=function () {
            document.getElementById("span01").innerText=""
        }

    </script>
</div>
</body>
</html>

Servlet下

登录LoginServlet

package com.StudentTest.Servlet;

import com.StudentTest.pojo.User;
import com.StudentTest.service.FileService;
import com.StudentTest.service.FileServiceImpl;
import com.StudentTest.service.LoginService;
import com.StudentTest.service.LoginServiceImpl;

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.ArrayList;

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String u_id=null,u_pwd=null;
        User u = new User();
        try{//非数字异常判断
          u_id = req.getParameter("u_id");
           u_pwd = req.getParameter("u_pwd");
            u.setU_id(Integer.valueOf(u_id));
            u.setU_pwd(u_pwd);
      }catch (Exception e){
            req.setAttribute("error", "你输入的不是数字");
            //错误就回到主界面
            req.getRequestDispatcher("login.jsp").forward(req, resp);
      }

        //实现登录服务层的业务逻辑层，从服务层service到持久层dao
        LoginService ls = new LoginServiceImpl();
        //返回user这样可以看到登录的用户是谁
        /**
         * 如果user为空说明账号密码不一致，跳转到登录界面
         * 不为空说明账号密码一致，跳转到主界面
         */
        User user = null;
        try {
            user = ls.loginService(u);
        } catch (Exception e) {
            e.printStackTrace();
        }

        if (user != null) {
            FileService fs=new FileServiceImpl();
            //查看所有数据
            ArrayList<User> arrUser=fs.getAllStudent();
            //将这些数据转发到前端
            req.setAttribute("arr",arrUser);
            req.setAttribute("user", user);
            //跳转到主界面
            req.getRequestDispatcher("mainPage.jsp").forward(req, resp);
        } else {
            req.setAttribute("error", "密码不匹配");
            req.getRequestDispatcher("login.jsp").forward(req, resp);
        }
    }
}

查找SearchServlet

package com.StudentTest.Servlet;

import com.StudentTest.pojo.User;
import com.StudentTest.service.FileService;
import com.StudentTest.service.FileServiceImpl;
import com.StudentTest.service.LoginService;
import com.StudentTest.service.LoginServiceImpl;

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.ArrayList;

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String u_id=null,u_pwd=null;
        User u = new User();
        try{//非数字异常判断
          u_id = req.getParameter("u_id");
           u_pwd = req.getParameter("u_pwd");
            u.setU_id(Integer.valueOf(u_id));
            u.setU_pwd(u_pwd);
      }catch (Exception e){
            req.setAttribute("error", "你输入的不是数字");
            //错误就回到主界面
            req.getRequestDispatcher("login.jsp").forward(req, resp);
      }

        //实现登录服务层的业务逻辑层，从服务层service到持久层dao
        LoginService ls = new LoginServiceImpl();
        //返回user这样可以看到登录的用户是谁
        /**
         * 如果user为空说明账号密码不一致，跳转到登录界面
         * 不为空说明账号密码一致，跳转到主界面
         */
        User user = null;
        try {
            user = ls.loginService(u);
        } catch (Exception e) {
            e.printStackTrace();
        }

        if (user != null) {
            FileService fs=new FileServiceImpl();
            //查看所有数据
            ArrayList<User> arrUser=fs.getAllStudent();
            //将这些数据转发到前端
            req.setAttribute("arr",arrUser);
            req.setAttribute("user", user);
            //跳转到主界面
            req.getRequestDispatcher("mainPage.jsp").forward(req, resp);
        } else {
            req.setAttribute("error", "密码不匹配");
            req.getRequestDispatcher("login.jsp").forward(req, resp);
        }
    }
}

删除DeleteServlet

package com.StudentTest.Servlet;

import com.StudentTest.pojo.User;
import com.StudentTest.service.FileService;
import com.StudentTest.service.FileServiceImpl;

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.ArrayList;

@WebServlet("/deleteServlet")
public class DeleteServlet  extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");
        String del=req.getParameter("v");
        //获取登录人信息
         String adm=req.getParameter("id");
         //访问service层，在service层创建对应的方法
        FileService fs=new FileServiceImpl();
        ArrayList<User> list=fs.getAllStudent();
        //获取登录人员信息
        User u = fs.getAdmint(adm);
        //service层调用方法，转到dao层执行sql语句
        boolean user=fs.delUser(del);
        String tip="";
        if(user){
           tip="删除成功";
        }else {
            tip="删除失败";
        }
        //发送到前端
        req.setAttribute("user", u);
        req.setAttribute("arr", list);
        req.setAttribute("tip", tip);
        req.getRequestDispatcher("mainPage.jsp").forward(req, resp);
    }
}

修改ChangeServlet

package com.StudentTest.Servlet;

import com.StudentTest.pojo.User;
import com.StudentTest.service.FileService;
import com.StudentTest.service.FileServiceImpl;

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.ArrayList;

@WebServlet("/changeUser")
public class ChangeServlet  extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");
        String id=req.getParameter("u_id");
        String pwd=req.getParameter("u_pwd");
        String phone=req.getParameter("u_phone");
        String name=req.getParameter("u_name");
        FileService fs=new FileServiceImpl();
        User user=new User(name,Integer.valueOf(id),pwd,phone);
        String adm=req.getParameter("id");
        //获取登录人员信息
        User u = fs.getAdmint(adm);
        System.out.println(u);
        boolean flag=fs.changeUser( user);

        ArrayList<User> list=fs.getAllStudent();
        String tip="";
        if (flag){
            tip="修改成功";
        }else{
            tip="修改失败";
        }
        //发送到前端

        req.setAttribute("tip",tip);
        req.setAttribute("user", u);
        req.setAttribute("arr", list);

        req.getRequestDispatcher("mainPage.jsp").forward(req, resp);
    }
}

添加addServlet

package com.StudentTest.Servlet;

import com.StudentTest.pojo.User;
import com.StudentTest.service.FileService;
import com.StudentTest.service.FileServiceImpl;

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.ArrayList;

@WebServlet("/addUser")
public class AddServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");
           String id=req.getParameter("u_id");
           String pwd=req.getParameter("u_pwd");
           String phone=req.getParameter("u_phone");
          String name=req.getParameter("u_name");
        FileService fs=new FileServiceImpl();
        User user=new User(name,Integer.valueOf(id),pwd,phone);
        String adm=req.getParameter("id");
        //获取登录人员信息
        User u = fs.getAdmint(adm);
        System.out.println(u);
      boolean flag=fs.addUser( user);

        ArrayList<User> list=fs.getAllStudent();
        String tip="";
        if (flag){
            tip="添加成功";
        }else{
            tip="添加失败";
        }
        //发送到前端

      req.setAttribute("tip",tip);
        req.setAttribute("user", u);
        req.setAttribute("arr", list);

        req.getRequestDispatcher("mainPage.jsp").forward(req, resp);

    }
}

Service下

FileServic接口下

package com.StudentTest.service;

import com.StudentTest.pojo.User;

import java.util.ArrayList;

public interface FileService {
    ArrayList<User> getAllStudent();

    User searchIdName(String v);
    User getAdmint(String id);
 boolean delUser(String del);
  boolean addUser(User user);

    boolean changeUser(User user);
    User loginService(User u) throws Exception;
}

FileServiceImpl实现类下

package com.StudentTest.service;

import com.StudentTest.Dao.FileDao;
import com.StudentTest.Dao.FileDaoImpl;
import com.StudentTest.pojo.User;

import java.util.ArrayList;

public class FileServiceImpl implements FileService {
    FileDao fd= new FileDaoImpl();
    @Override
    public ArrayList<User> getAllStudent() {
        /**
         * 访问持久层
         */

        return fd.getAllStudent();
    }

    @Override
    public User searchIdName(String v) {

        return fd.searchIdName( v);
    }

    @Override
    public User getAdmint(String id) {
        return fd.getAdmint(id);
    }

    @Override
    public boolean delUser(String del) {
        return fd.delUser(del );
    }

    @Override
    public boolean addUser(User user) {
        return fd.addUser(user);
    }

    @Override
    public boolean changeUser(User user) {
        return fd.changeUser(user);
    }

    @Override
    public User loginService(User u) throws Exception {
        return fd.loginDao( u);
    }


}

pojo下

User学生类

package com.StudentTest.pojo;

public class User {
    private String u_name;
    private int u_id;
    private String u_pwd;
    private String u_phone;
    private int u_role;
    private int u_isdelete;

    public User() {
    }
    public User(String u_name, int u_id, String u_pwd, String u_phone) {
        this.u_name = u_name;
        this.u_id = u_id;
        this.u_pwd = u_pwd;
        this.u_phone = u_phone;

    }

    public User(String u_name, int u_id, String u_pwd, String u_phone, int u_role, int u_isdelete) {
        this.u_name = u_name;
        this.u_id = u_id;
        this.u_pwd = u_pwd;
        this.u_phone = u_phone;
        this.u_role = u_role;
        this.u_isdelete = u_isdelete;
    }

    public String getU_name() {
        return u_name;
    }

    public void setU_name(String u_name) {
        this.u_name = u_name;
    }

    public int getU_id() {
        return u_id;
    }

    public void setU_id(int u_id) {
        this.u_id = u_id;
    }

    public String getU_pwd() {
        return u_pwd;
    }

    public void setU_pwd(String u_pwd) {
        this.u_pwd = u_pwd;
    }

    public String getU_phone() {
        return u_phone;
    }

    public void setU_phone(String u_phone) {
        this.u_phone = u_phone;
    }

    public int getU_role() {
        return u_role;
    }

    public void setU_role(int u_role) {
        this.u_role = u_role;
    }

    public int getU_isdelete() {
        return u_isdelete;
    }

    public void setU_isdelete(int u_isdelete) {
        this.u_isdelete = u_isdelete;
    }

    @Override
    public String toString() {
        return "User{" +
                "u_name='" + u_name + ''' +
                ", u_id=" + u_id +
                ", u_pwd='" + u_pwd + ''' +
                ", u_phone='" + u_phone + ''' +
                ", u_role=" + u_role +
                ", u_isdelete=" + u_isdelete +
                '}';
    }
}

Dao下

FileDao接口下

package com.StudentTest.Dao;

import com.StudentTest.pojo.User;

import java.util.ArrayList;

public interface FileDao {
    ArrayList<User> getAllStudent();

    User searchIdName(String v);

    User getAdmint(String id);

    boolean delUser(String del);


   boolean addUser(User user);

    boolean changeUser(User user);

        User loginDao(User u) throws Exception;

}

FileDaoImpl实现类下

package com.StudentTest.Dao;

import com.StudentTest.pojo.User;
import com.utils.JDBCUtils;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;

public class FileDaoImpl implements FileDao {

    @Override
    public User loginDao(User u) throws SQLException, ClassNotFoundException {
        /**在这写数据库的内容
         * 获取链接对象，获取sql语句
         */
        int id=u.getU_id();
        String pwd=u.getU_pwd();
//       //访问数据库
//        User user=new User("慧宝",1001,"520","15216123240",1,0);
        Connection connection= JDBCUtils.getConnection();
        PreparedStatement pre =null;
        ResultSet res =null;
        String sql="select *from user where u_id="+id+" and u_pwd='"+pwd+"'";
        try{
            pre= connection.prepareStatement(sql);
            res=pre.executeQuery();
            User user=new User();
            while(res.next()){
                user.setU_id(res.getInt("u_id"));
                user.setU_name(res.getString("u_name"));
                user.setU_pwd(res.getString("u_pwd"));
                user.setU_phone(res.getString("u_phone"));
                user.setU_role(res.getInt("u_role"));
                user.setU_isdelete(res.getInt("u_isdelete"));
                return user;
            }

        } catch (SQLException s){
            s.printStackTrace();
        }

        return null;
    }


    @Override
    public ArrayList<User> getAllStudent() {
        ArrayList<User> arr=new ArrayList<>();

        Connection connection= null;
        try {
            connection = JDBCUtils.getConnection();
        } catch (Exception e) {

        }
        PreparedStatement pre =null;
            ResultSet res =null;
            //u_role为1表示普通用户，为0为管理员，u_isdelete为0表示还在，为1表示已删除
            String sql="select *from user where u_role=1 and u_isdelete=0 ";
            try{
                pre= connection.prepareStatement(sql);
                res=pre.executeQuery();
                while(res.next()){
                    User user=new User();
                    user.setU_id(res.getInt("u_id"));
                    user.setU_name(res.getString("u_name"));
                    user.setU_pwd(res.getString("u_pwd"));
                    user.setU_phone(res.getString("u_phone"));
                    user.setU_role(res.getInt("u_role"));
                    user.setU_isdelete(res.getInt("u_isdelete"));
                    arr.add(user);
                }
                return arr;

            } catch (SQLException s){
                s.printStackTrace();
            }

            return null;
        }

    @Override
    public User searchIdName(String v) {
        /**
         * sql
         */
        Connection connection= null;
        try {
            connection = JDBCUtils.getConnection();
        } catch (Exception e) {

        }
        PreparedStatement pre =null;
        ResultSet res =null;
        //u_role为1表示普通用户，为0为管理员，u_isdelete为0表示还在，为1表示已删除
        String sql="select *from user where u_id ='"+v+"'or+ u_name ='"+v+"' ";
        try{
            pre= connection.prepareStatement(sql);
            res=pre.executeQuery();
            while(res.next()){
                User user=new User();
                user.setU_id(res.getInt("u_id"));
                user.setU_name(res.getString("u_name"));
                user.setU_pwd(res.getString("u_pwd"));
                user.setU_phone(res.getString("u_phone"));
                user.setU_role(res.getInt("u_role"));
                user.setU_isdelete(res.getInt("u_isdelete"));

                return  user;
            }

        } catch (SQLException s){
            s.printStackTrace();
        }

        return null;
    }
    @Override
    public User getAdmint(String id) {
        Connection connection= null;
        try {
            connection = JDBCUtils.getConnection();
        } catch (Exception e) {

        }
        PreparedStatement pre =null;
        ResultSet res =null;
        String sql="select *from user where u_id ='"+id+"'or+ u_name ='"+id+"' ";
       try{
            pre= connection.prepareStatement(sql);
            res=pre.executeQuery();
            while(res.next()){
                User user=new User();
                user.setU_id(res.getInt("u_id"));
                user.setU_name(res.getString("u_name"));
                return user;
            }

        } catch (SQLException s){
            s.printStackTrace();
        }
        return null;
    }

    @Override
    public boolean delUser(String del) {
        Connection connection= null;
        try {
            connection = JDBCUtils.getConnection();
        } catch (Exception e) {

        }
        PreparedStatement pre =null;
        ResultSet ress=null;
        int res=0;
        String sql="delete from user where u_id="+del;
        try{
            pre= connection.prepareStatement(sql);
            res=pre.executeUpdate();

         if(res>=0)return true;

        } catch (SQLException s){
            s.printStackTrace();
        }

        return false;
    }

    @Override
    public boolean addUser(User user) {
        Connection connection= null;
        try {
            connection = JDBCUtils.getConnection();
        } catch (Exception e) {

        }
        PreparedStatement pre =null;
        ResultSet ress=null;
        String name=user.getU_name();
         int id=user.getU_id();
         String pwd=user.getU_pwd();
         String phone=user.getU_phone();
        int res=0;
        //"insert into user values('"+user.getU_name()+"','"+user.getU_id()+"','"+user.getU_pwd()+"','"+user.getU_phone()+"')"
        String sql="insert into user(u_name,u_id,u_pwd,u_phone)n" +
                "values('"+name+"','"+id+"','"+pwd+"','"+phone+"')";
        try{
            pre= connection.prepareStatement(sql);
            res=pre.executeUpdate();
            System.out.println(res);
            if(res>=0)return true;

        } catch (SQLException s){
            s.printStackTrace();
        }

        return false;
    }

    @Override
    public boolean changeUser(User user) {
        Connection connection= null;
        try {
            connection = JDBCUtils.getConnection();
        } catch (Exception e) {

        }
        PreparedStatement pre =null;
        ResultSet ress=null;
        String name=user.getU_name();
        int id=user.getU_id();
        String pwd=user.getU_pwd();
        String phone=user.getU_phone();
        int res=0,res1=0;
        String sql1="delete from user where u_id="+id;

        try{
            pre= connection.prepareStatement(sql1);
            res=pre.executeUpdate();
            if (res>0){
                String sql="insert into user(u_name,u_id,u_pwd,u_phone)n" +
                        "values('"+name+"','"+id+"','"+pwd+"','"+phone+"')";
                pre= connection.prepareStatement(sql);
                res1=pre.executeUpdate();
            }
            System.out.println(res);
            if(res1>0)return true;

        } catch (SQLException s){
            s.printStackTrace();
        }

        return false;

    }


}

utils下

JDBCUtils

package com.utils;

import java.sql.*;

public class JDBCUtils {
    public static Connection getConnection() throws SQLException, ClassNotFoundException {
        Class.forName("com.mysql.cj.jdbc.Driver");
        String url="jdbc:mysql://localhost:3306/studenttest?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone = GMT";
        String username="root";
        String password="123456";
        Connection conn= DriverManager.getConnection(url,username,password);
        return conn;
    }

    public static void release(Statement stmt,Connection conn){
        if(stmt!=null){
            try{
                stmt.close();
            }catch(SQLException e){
                e.printStackTrace();
            }
            stmt=null;
        }
        if(conn!=null){
            try{
                conn.close();
            }catch (SQLException e){
                e.printStackTrace();
            }
            conn=null;
        }
    }

    public static void release(ResultSet rs,Statement stmt,Connection conn){
        if(rs!=null){
            try{
                rs.close();
            }catch (SQLException e){
                e.printStackTrace();
            }
            rs=null;
        }
        release(stmt,conn);
    }
}

还有写web-inf下lib下的jar包

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