1.傳統(tǒng)的JDBC編程

1.創(chuàng)建數據庫

create database mybatis charset utf8 collate utf8_general_ci;

CREATE TABLE `tb_user` (
  `ID` int(11) NOT NULL AUTO_INCREMENT,
  `NAME` varchar(18) DEFAULT NULL,
  `SEX` char(2) DEFAULT NULL,
  `AGE` int(11) DEFAULT NULL,
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

2.Java后臺代碼

• 1.引入mysql jar包

compile group: 'mysql', name: 'mysql-connector-java', version: '6.0.6'

• 2.創(chuàng)建java實體類型

public class User {
    private int id;

    private String name;

    private String sex;

    private int age;

   //省略get set

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", age=" + age +
                '}';
    }

• 3.編寫JDBC代碼

創(chuàng)建數據庫鏈接

private Connection getConnection() throws ClassNotFoundException, SQLException {
    Connection connection = null;
    Class.forName("com.mysql.jdbc.Driver");
    String url = "jdbc:mysql://localhost:3306/mybatis";
    String user = "root";
    String password = "root";
    connection = DriverManager.getConnection(url, user, password);
    return connection;
}

創(chuàng)建關閉數據對象銷毀方法

private void close(ResultSet rs, Statement statement, Connection connection) throws SQLException {
    if (rs != null && !rs.isClosed())
        rs.close();
    if (statement != null && !statement.isClosed())
        statement.close();
    if (connection != null && !connection.isClosed())
        connection.close();
}

編寫獲取對象的方法

public User getUser(int id) throws SQLException {
    User user = new User();
    Connection connection = null;
    PreparedStatement statement = null;
    ResultSet rs = null;
    try {
        connection = getConnection();
        statement = connection.prepareStatement("select * from tb_user where id=?");
        statement.setInt(1, id);
        rs = statement.executeQuery();
        while (rs.next()) {
            int uId = rs.getInt("ID");
            String name = rs.getString("NAME");
            String sex = rs.getString("SEX");
            int age = rs.getInt("AGE");
            user.setId(uId);
            user.setName(name);
            user.setSex(sex);
            user.setAge(age);
            break;
        }
    } catch (Exception ex) {
        ex.printStackTrace();
    } finally {
        close(rs, statement, connection);
    }
    return user;
}

運行測試

public static void main(String[] args) {
    try {
        JdbcExample example = new JdbcExample();
        User user = example.getUser(1);
        System.out.println(user.toString());
    } catch (Exception ex) {
        ex.printStackTrace();
    }
}

從上面的代碼中，我們可以看出傳統(tǒng)的JDBC的整個過程是:

• 1.使用JDBC編程需要連接數據庫，注冊驅動和數據庫信息
• 2.操作Connection，打開Statement對象
• 3，通過Statement對象執(zhí)行SQL，返回結果到ResultSet對象
• 4.使用ResultSet讀取數據，通過代碼轉換為具體的POJO對象
• 5.關閉數據庫連接

缺點

• 1.需要先連接，然后處理JDBC底層事務
• 2.還需要操作Connection對象，Statement對象，ResultSet對象
• 3.還需要獲取ResultSet對象進行對POJO的映射
• 4.還需要處理異常以及關閉數據資源

2.ORM框架

對于快速迭代的項目而言，增加了巨大的工作量。于是誕生了ORM(Object Relational Mapping)的概念

解決數據庫數據和POJO對象的相互映射。可以迅速將數據庫表的數據轉化為POJO

ORM映射模型

3.MyBatis

Mybatis是一個半自動映射的框架，因為它需要手動進行匹配提供POJO、SQL和映射關系。

• MyBatis的映射文件包含

1. SQL
2. 映射規(guī)則
3. POJO

4.實戰(zhàn)代碼

• 引入jar包

compile group: 'org.mybatis', name: 'mybatis', version: '3.4.4'

• 創(chuàng)建Dao User接口

package dao;

import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;

import java.util.List;

import model.User;

@Mapper
public interface UserDao {
    User getUser(int id);
}

• 創(chuàng)建UserMapper.xml文件

在resource文件夾下面創(chuàng)建mapper文件夾

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="dao.UserDao">
   <select id="getUser" parameterType="int" resultType="model.User">
       select * from tb_user where id=#{id};
   </select>
</mapper>

• 創(chuàng)建mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
                <property name="username" value="root" />
                <property name="password" value="root" />
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="mapper/UserDao.xml" />
    </mappers>
</configuration>

• 操作代碼

import model.User;
import dao.UserDao;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;

/**
 * Created on 2017-08-06.
 */
public class MyBatisClient {
    public static void main(String[] args) throws IOException {
        //讀取mybatis-config.xml文件
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        //初始化mybatis，創(chuàng)建SqlsessionFactory類的實例
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //創(chuàng)建Sqlsession實例
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //獲取User Dao的實例
        UserDao dao = sqlSession.getMapper(UserDao.class);
        User user = dao.getUser(1);
        System.out.println(user.toString());
    }
}