Java持久化数据的方式——JDBC&ORM&JPA(深度好文)

JDBC

什么是JDBC？

有了JDBC之后的好处

JDBC完成用户的CURD

jdbc.properties：配置连接数据库的四大基本参数。

className=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/test
username=root
password=root

User实体类

import lombok.Data;

@Data
public class User {
   
    private Integer uid;
    private String uname;
    private String pwd;
    private Integer sex;
    private Integer age;
}

sql建表语句

CREATE TABLE `users` (
  `uid` int(10) NOT NULL AUTO_INCREMENT COMMENT '用户id',
  `uname` varchar(255) DEFAULT NULL COMMENT '用户姓名',
  `pwd` varchar(255) DEFAULT NULL COMMENT '用户密码',
  `sex` int(1) DEFAULT NULL COMMENT '用户性别，1：男，0：女',
  `age` int(3) DEFAULT NULL COMMENT '用户年龄',
  PRIMARY KEY (`uid`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

CURD代码

package cn.xxxq.jdbc.statement;

import cn.xxxq.jdbc.domain.User;

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

/**
 *  使用Statement对象执行增删改查SQL语句，有SQL注入的风险。
 */
public class JDBC_CURD_Statement {
   

    private static String className;
    private static String url;
    private static String username;
    private static String password;
	
	/*
		使用静态代码块在类加载的时候读取外部属性文件
	*/
    static {
   
        InputStream in = JDBC_CURD_Statement.class.getClassLoader().getResourceAsStream("jdbc.properties");
        Properties properties = new Properties();
        try {
   
            properties.load(in);
            className = properties.getProperty("className");
            url = properties.getProperty("url");
            username = properties.getProperty("username");
            password = properties.getProperty("password");
        } catch (IOException e) {
   
            e.printStackTrace();
        } finally {
   
            if (in!=null)
                try {
   
                    in.close();
                } catch (IOException e) {
   
                    e.printStackTrace();
                }
        }
    }

    public static void main(String[] args) {
   
        selectAllUser();
//        insert();
//        update();
//        delete();
    }
	
	/**
     *  查询所有用户
     */
    public static void selectAllUser(){
   
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try {
   
            //注册驱动
            Class.forName(className);
            //获取连接对象
            connection = DriverManager.getConnection(url, username, password);
            //获取SQL执行对象
            statement = connection.createStatement();
            /*执行SQL语句*/
            String sql = "select * from users";
            resultSet = statement.executeQuery(sql);
            while (resultSet.next()){
   
                int uid = resultSet.getInt("uid");
                int sex = resultSet.getInt("sex");
                int age = resultSet