Hi MyBatis ~

学习笔记 : 初识MyBatis

简介 : MyBatis的前身是iBATIS,是Clinton Begin在2001年发起的一个开源项目,最初侧重于密码软件的开发,后来发展成为一款基于Java的持久层框架.2004年,Clinton将iBATIS的名字和源码捐赠给了Apache软件基金会.2010年,核心开发团队决定离开Apache软件基金会,并且将iBATIS该名为MyBatis.

MyBatis 工作原理

MyBatis框架执行流程图如下所示 :

从MyBatis框架执行流程图中可得知,MyBatis框架在操作数据库时,大体经过了8个步骤.下面对每一步进行详解哟 ~

1. 读取MyBatis配置文件mybatis-config.xml.其作为MyBatis的全局配置文件,配置了MyBatis的运行环境等信息,其中主要内容是获取数据库连接.

2. 加载映射配置文件Mapper.xml.既SQL映射文件,该文件配置了操作数据库的SQL语句,需要在mybatis-config.xml中加载才能执行.mybatis-config.xml可以加载多个配置文件,每个配置文件对应数据库中的一张表.

3. 构建会话工厂.通过MyBatis的环境等配置信息构建会话工厂SqlSessionFactory.

4. 创建SqlSession对象.由会话工厂创建SqlSession对象,该对象中包含了执行SQL的所有方法.

5. MyBatis底层定义了一个Executor接口来操作数据库,它会根据SqlSession传递的参数动态地生成需要执行的SQL语句,同时负责查询缓存的维护.

6. 在Executor接口的执行方法中,包含一个MappedStatement类型的参数,该参数是对映射信息的封装,用于存储要映射的SQL语句的id,参数等.. Mapper.xml文件中一个SQL对应一个MappedStatement对象,SQL的id既是MappedStatement的id.

7. 输入参数映射,其过程类似于JDBC编程中对preparedStatement对象设置参数的过程.

8. 输出参数映射,其过程类似于JDBC编程中对结果的解析处理过程.

MyBatis 入门程序

1. User.java : 一个简单Java bean

   package pers.huangyuhui.mybatis.bean;
   
   /**
    * @ClassName: User
    * @Description: 封装用户信息
    * @author: HuangYuhui
    * @date: May 9, 2019 5:07:23 PM
    *
    */
   public class User {
   
   	private Integer id;
   	private String name;
   	private String gender;
   	private String email;
   
   	public Integer getId() {
   		return id;
   	}
   
   	public void setId(Integer id) {
   		this.id = id;
   	}
   
   	public String getName() {
   		return name;
   	}
   
   	public void setName(String name) {
   		this.name = name;
   	}
   
   	public String getGender() {
   		return gender;
   	}
   
   	public void setGender(String gender) {
   		this.gender = gender;
   	}
   
   	public String getEmail() {
   		return email;
   	}
   
   	public void setEmail(String email) {
   		this.email = email;
   	}
   
   	@Override
   	public String toString() {
   		return "User [id=" + id + ", name=" + name + ", gender=" + gender + ", email=" + email + "]";
   	}
   
   }

2. db.properties : 数据库配置信息文件.

   #database configuration information
   jdbc.driver=com.mysql.cj.jdbc.Driver
   jdbc.url=jdbc:mysql://LOCALHOST/MyBatis?useSSL=false&serverTimezone=UTC&allowPublicKeyRetrieval=true
   jdbc.username=root
   jdbc.password=GoodTime

3. mybatis-config.xml : MyBatis核心配置文件

   <?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>
   	<!-- 读取数据库配置文件 -->
   	<properties resource="db.properties" />
   	<!-- 配置环境-默认环境id为MySQL -->
   	<environments default="MySQL">
   		<environment id="MySQL">
   			<!-- 使用JDBC事务管理 -->
   			<transactionManager type="JDBC" />
   			<!-- 数据库连接池 -->
   			<dataSource type="POOLED">
   				<property name="driver" value="${jdbc.driver}" />
   				<property name="url" value="${jdbc.url}" />
   				<property name="username" value="${jdbc.username}" />
   				<property name="password" value="${jdbc.password}" />
   			</dataSource>
   		</environment>
   	</environments>
   	<!-- 将sql映射文件注册到全局配置文件中 -->
   	<mappers>
   		<mapper resource="UserMapper.xml" />
   	</mappers>
   </configuration>

4. UserTest.java : 测试类

   package pers.huangyuhui.mybatis.bean.test;
   
   import java.io.IOException;
   import java.io.InputStream;
   
   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 org.junit.jupiter.api.Test;
   
   import pers.huangyuhui.mybatis.bean.User;
   
   /**
    * @ClassName: UserTest
    * @Description: Test Mybatis
    * @author: HuangYuhui
    * @date: May 9, 2019 5:26:52 PM
    *
    */
   public class UserTest {
   
   	InputStream inputStream;
   	SqlSessionFactory sqlSessionFactory;
   	SqlSession sqlSession;
   
   	@Test
   	public void test() {
   
   		try {
   			// 读取配置文件
   			inputStream = Resources.getResourceAsStream("mybatis-config.xml");
   			// 根据配置文件构建会话工厂对象
   			SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
   			// 通过SqlSessionFactory创建SqlSession
   			sqlSession = sqlSessionFactory.openSession();
   			// 执行映射文件中定义的SQL并返回映射结果
   			User user = sqlSession.selectOne("Namespace.UserInfoMapper.SelectUserInfoByID", 1);
   
   			System.out.println(user);
   
   		} catch (IOException e) {
   			e.printStackTrace();
   		} finally {
   			sqlSession.close();
   		}
   
   	}
   }

5. log4j.properties : 日志文件(便于查看MyBatis操作数据库的过程).

   #Global configuration
   log4j.rootLogger=DEBUG,stdout
   #Log configuration
   log4j.logger.pers.huangyuhui.mybatis.bean.test=TRACE
   #Console configuration
   log4j.appender.stdout=org.apache.log4j.ConsoleAppender
   log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
   log4j.appender.stdout.layout.layout.ConversionPattern=%5p [%t] - %m%n

6. 程序运行结果如下所示

   Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
   PooledDataSource forcefully closed/removed all connections.
   PooledDataSource forcefully closed/removed all connections.
   PooledDataSource forcefully closed/removed all connections.
   PooledDataSource forcefully closed/removed all connections.
   Opening JDBC Connection
   Created connection 1238080693.
   Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@49cb9cb5]
   
   ==>  Preparing: select id,name,gender,email from Test_MyBatis where id = ? 
   ==> Parameters: 1(Integer)
   <==      Total: 1
   User [id=1, name=YUbuntu0109, gender=M, email=Gentleman_0109@outlook.com]
   
   Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@49cb9cb5]
   Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@49cb9cb5]
   Returned connection 1238080693 to pool.