JDBC基础----用户登录案例

概念：JDBC（java database connectivity），就是一种API，提供了规范，定义了接口和类，用于方便操作不同数据库

掌握JDBC的基础就在于四个类

1. DriverManager                        驱动类
2. Connection                           连接类
3. PreparedStatement                    语句类
4. ResultSet                            结果类

驱动类：因为市面上有很多的数据库产品，那么相应的就会有许多的驱动，这些都是由数据库厂商提供的
连接类：这是数据库与程序之间的桥梁
语句类：用于编写各种SQL语句来操作数据库
结果类：自然是用来接收返回的数据的

其中重点的方法：

//1. 加载mysql驱动类
Class.forName("com.mysql.jdbc.Driver");


//2. 获得连接对象
/**
'jdbc:mysql://'   为连接mysql固定写法
'localhost:3306/' 表示为连接本机IP的mysql的默认3306端口
'test'            要连接的数据库名                 
*/
String url = "jdbc:mysql://localhost:3306/test"; 
String user = "abc";
String password = "123";
Connection conn = DriverManager.getConnection(url, user, password);


//3. 准备SQL语句
/**
sql中的*号可以使用setString()方法被替换成条件被执行
*/
String sql = "SELECT * FROM user WHERE name = ? AND pwd = ?";
PreparedStatement ps = conn.prepareStatement(sql);
ps.setString(1, name);
ps.setString(2, pwd);


//4. 处理结果
ResultSet rs = ps.executeQuery(); //执行查询语句，接收返回结果
while(rs.next()) { 一笔一笔循环取值，若没有值，返回false
    String s = rs.getString(1);  //取出当前行中第一个字段 
    Int i = rs.getInt(2);  //取出当前行中第二个字段
    ...
}

//5. 别忘了关闭资源
rs.close();
ps.close();
conn.close();

贴上代码

package util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ResourceBundle;


public class DBUtils {
    private static String driveClass;
    private static String url;
    private static String user;
    private static String password;

    static {
        url = "jdbc:mysql:///test?useSSL=false";
        user = "abc";
        password = "123";
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch(ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    //得到连接
    public static Connection getConnection() throws SQLException{
        return DriverManager.getConnection(url, user, password);    
    }

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

        if(stmt != null) {
            try {
                stmt.close();
            } catch(SQLException e) {
                e.printStackTrace();
            }
        }

        if(conn != null) {
            try {
                conn.close();
            } catch(SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

package service;

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

import entity.User;
import util.DBUtils;

public class DoLogin {

    public User findUser(String name, String password) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        User u = null;
        try {
            conn = DBUtils.getConnection();
            String sql = "SELECT * FROM user WHERE name = ? AND pwd = ?";
            ps = conn.prepareStatement(sql);
            ps.setString(1, name);
            ps.setString(2,pwd);

            rs = ps.executeQuery();
            if(rs.next()) {
                u = new User();
                u.setName(rs.getString(1));
                u.setPassword(rs.getString(2));
            }
        } catch(SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtils.closeAll(rs, ps, conn);
        }

        return u;
    }

}

package client;

import java.util.Scanner;

import entity.User;
import service.DoLogin;

public class Login {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        System.out.println("请输入用户名");
        Scanner scan = new Scanner(System.in);
        String name = scan.nextLine();
        System.out.println("请输入密码");
        String password = scan.nextLine();

        DoLogin dl = new DoLogin();
        User u = dl.findUser(name, password);

        if(u != null) {
            System.out.println("欢迎登陆" + " " + u.getName());
        } else {
            System.out.println("用户名或者密码有误");
        }
    }

}

package entity;

public class User {
    private String name;
    private String password;

    public User() {

    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return password;
    }

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

    @Override
    public String toString() {
        return "User [name=" + name + ", password=" + password + "]";
    }
}

JDBC基础----用户登录案例

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