Java的JDBC操作

Java的JDBC操作

1、基本操作

// Main.java
package com.company;

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

public class Main {
    public static void main(String[] args) throws Exception {
        //1. 注册驱动
        //Class.forName("com.mysql.jdbc.Driver");
        //2. 获取连接
        String url = "jdbc:mysql://127.0.0.1:3306/myDB";
        String username = "root";
        String password = "root";
        Connection conn = DriverManager.getConnection(url, username, password);
        //3. 定义sql
        String sql = "update account set money = 2000 where id = 1";
        //4. 获取执行sql的对象 Statement
        Statement stmt = conn.createStatement();
        //5. 执行sql
        int count = stmt.executeUpdate(sql);//受影响的行数
        //6. 处理结果
        System.out.println(count);
        //7. 释放资源
        stmt.close();
        conn.close();
    }
}

2、对于数据库的增删改来说，提交均用stmt.executeupdate(sql)，返回的是受影响的行数。对于查，比如select * from users， 使用ResultSet rs = stmt.executequery(sql)，返回的是符合条件的所有数据

// Main.java
package com.company;

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

public class Main {
    public static void main(String[] args) throws  Exception {
        //1. 注册驱动
        //Class.forName("com.mysql.jdbc.Driver");
        //2. 获取连接：如果连接的是本机mysql并且端口是默认的 3306 可以简化书写
        String url = "jdbc:mysql://127.0.0.1:3306/myDB";
        String username = "root";
        String password = "1234";
        Connection conn = DriverManager.getConnection(url, username, password);
        //3. 定义sql
        String sql = "select * from account";
        //4. 获取statement对象
        Statement stmt = conn.createStatement();
        //5. 执行sql
        ResultSet rs = stmt.executeQuery(sql);
        //6. 处理结果， 遍历rs中的所有数据
        // 6.1 光标向下移动一行，并且判断当前行是否有数据
        while (rs.next()){
            //6.2 获取数据  getXxx()
            int id = rs.getInt("id");
            String name = rs.getString("name");
            double money = rs.getDouble("money");

            System.out.println(id);
            System.out.println(name);
            System.out.println(money);

            System.out.println("--------------");
        }

        //7. 释放资源
        rs.close();
        stmt.close();
        conn.close();
    }
}

3、PreparedStatement

PreparedStatement作用：预编译SQL语句并执行：预防SQL注入问题

// 定义sql
String sql = "select * from tb_user where username = ? and password = ?";
// 获取pstmt对象
PreparedStatement pstmt = conn.prepareStatement(sql);
// 设置？的值
pstmt.setString(1,name);
pstmt.setString(2,pwd);
// 执行sql
ResultSet rs = pstmt.executeQuery();