java连接数据库，实现用户管理

User类：

package com.pojo;

public class User {
    private int id;
    private String username;
    private String password;

    public User(int id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

GetConnection类：

package com.util;

import java.sql.Connection;
import java.sql.DriverManager;

public class GetConnection {
    private static String address="jdbc:mysql://localhost:3306/数据库名?useSSL=false&serverTimezone=UTC";
    private static String dataBaseName="用户名";
    private static String dataBasePwd="密码";

    public static Connection GetConn(){
        Connection conn=null;
        if(conn==null){

            try {
                //加载jdbc驱动
                Class.forName("com.mysql.cj.jdbc.Driver");
                //连接数据库
                conn= DriverManager.getConnection(address,dataBaseName,dataBasePwd);
            } catch (Exception e) {
                e.printStackTrace();
                System.out.println("连接失败！");
            }

        }
        return conn;
    }
}

UserService类：//实现功能类

package com.service;

import com.util.GetConnection;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;

public class UserService {
    static Connection conn=null;
    static Statement stmt=null;
//登录
    public static String login(String uname, String pwd) throws Exception {
        String msg="登录失败";

        conn= GetConnection.GetConn();
        stmt=conn.createStatement();
        String sql="select * from user where username='"+uname+"' and password='"+pwd+"'";
        ResultSet rs=stmt.executeQuery(sql);

        if (rs.next()){
            msg="登录成功";
        }
        conn.close();
        stmt.close();
        return msg;

    }
    //注销
    public static String delUser(String name,String pwd) throws Exception {
        String msg="注销失败";
        if("不存在".equals(findUserName(name))){
            msg="用户名不存在";
        }else {
            if ("登录成功".equals(login(name,pwd))){
                conn=GetConnection.GetConn();
                stmt=conn.createStatement();
                String sql="delete from user where username='"+name+"'";
                int count=stmt.executeUpdate(sql);
                if (count>0){
                    msg="注销成功";
                }else {

                    msg="sql执行错误；注销失败";
                }
            }else {
                msg="验证密码错误；";
            }

        }
        conn.close();
        stmt.close();

        return msg;
    }
    //注册
    public static String register(String name,String pwd) throws Exception {
        String msg="注册失败";
        if ("存在".equals(name)){
           msg="用户名已存在";
        }else {
            conn=GetConnection.GetConn();
            stmt=conn.createStatement();
            String sql="insert into user(username,password) values('"+name+"','"+pwd+"');";
            int count=stmt.executeUpdate(sql);
            if (count>0){
                msg="注册成功";
            }else {

                msg="sql执行错误；注册失败";
            }
            conn.close();
            stmt.close();
        }

        return msg;
    }
    //查询用户名是否存在
    public static String findUserName(String name) throws Exception {
        String msg="不存在";
        conn=GetConnection.GetConn();
        stmt=conn.createStatement();
        String sql="select * from user where username='"+name+"'";
        ResultSet rs=stmt.executeQuery(sql);
        if (rs.next()){
            msg="存在";
        }
        conn.close();
        stmt.close();
        return msg;
    }


}

package com.test;

import com.service.UserService;

public class Test1 {//测试类
    public static void main(String[] args) throws Exception {
       // String result=UserService.login("aaa","123");
        ///String result1=UserService.findUserName("aaa");
       // String result2=UserService.register("sss","111");
        // String result2=UserService.register("sss","111");
        // String result2=UserService.register("sss","111");
        String result3=UserService.delUser("sss","111");
        System.out.println(result3);
    }
}