JDBC底层代码

JDBC（原始不考虑事务）

package cn.gts.jdbc;

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

import org.junit.Test;

import cn.gts.entity.User;

public class Jdbc {
    @Test
    public void jdbcTest() {
        Connection conn = null;
        PreparedStatement psmt = null;
        ResultSet rs = null;

        try {
            /*
             * jdbc四大配置参数
             * driverClassName：com.mysql.jdbc.Driver
             * url:jdbc:mysql://localhost:3306/test
             * username:root
             * password:123
             */
            //加载驱动
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql://localhost:3306/test";
            String username = "root";
            String password = "123";
            //得到连接
            conn = DriverManager.getConnection(url,username,password);

            //编写sql语句
            String sql = "select * from user where username = ?";
            //预编译sql语句
            psmt = conn.prepareStatement(sql);
            //设置参数值
            psmt.setString(1, "zhangSan");
            //执行sql语句得到结果集
            rs = psmt.executeQuery();
            //遍历结果集
            while(rs.next()) {
                //根据字段得到数据
                String username = rs.getString("username");
                String password = rs.getString("password");
                //封装
                User user = new User();
                user.setUsername(username);
                user.setPassword(password);

                System.out.println(user);
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                rs.close();
                psmt.close();
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

JDBC演示转账（事务案例）

public void transfer(boolean b) {
        Connection con = null;
        PreparedStatement pstmt = null;

        try {
            con = JdbcUtils.getConnection();
            //手动提交
            con.setAutoCommit(false);

            String sql = "update account set balance=balance+? where id=?";
            pstmt = con.prepareStatement(sql);

            //操作
            pstmt.setDouble(1, -10000);
            pstmt.setInt(2, 1);
            pstmt.executeUpdate();

            // 在两个操作中抛出异常
            if(b) {
                throw new Exception();
            }

            pstmt.setDouble(1, 10000);
            pstmt.setInt(2, 2);
            pstmt.executeUpdate();

            //提交事务
            con.commit();
        } catch(Exception e) {
            //回滚事务
            if(con != null) {
                try {
                    con.rollback();
                } catch(SQLException ex) {}
            }
            throw new RuntimeException(e);
        } finally {
            //关闭
            JdbcUtils.close(con, pstmt);//这个只是一个自己写的工具类而已
        }
    }