【mybatis】mybatis的工作原理

一、工作流程

• 1.系统启动会加载解析全局配置文件（如mybatis-config.xml），加载解析的信息存储在Configuration对象中
• 2.通过建造者模式完成配置文件的解析与SqlSessionFactory对象的创建
• 3.通过SqlSessionFactory对象（是单例的）获取SqlSession对象
• 4.通过SqlSession中的api来操作数据库，有两种方式，可以通过名称空间和标签的id拼接成一个唯一的statement，还可以通过sqlSesion.getMapper拿到代理对象，通过代理对象去操作
• 5.关掉sqlSession，清空缓存

二、说明

2.1 构建SqlSessionFactory

• 1.每个基于mybatis的应用都是以一个SqlSessionFactory的实例为核心的。SqlSessionFactory的实例可以通过SqlSessionFactoryBuilder获得

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

• 2.SqlSessionFactoryBuilder可以从XML配置文件或一个预先配置的Configuration实例来构建出SqlSessionFactory实例

• 3.从XML文件中构建SqlSessionFactory实例，建议使用类路径下的资源文件进行配置。
  

• 4.也可以使用任意的输入流（InputStream）实例，例如文件路径字符串（file://）或者数据库URL构造输入流（xml格式与configuration格式）

• 5.使用mybatis中Resource工具类，能简化从类路径或其它位置加载资源文件

• 6.xml配置文件包括：获取数据库连接实例的数据源（DataSource）、决定事务作用域、控制方法的事务管理器（TransactionManager)。environment元素包含事务管理和连接池的配置。mappers元素包含映射器（mapper）,映射器包含了sql代码和映射定义信息

2.2 SqlSession的获取

• 1.通过SqlSession sqlSession = sqlSessionFactory.openSession();得到sqlSession

2.3 SqlSession执行语句

• 1.通过sqlSession.api(“名称空间.标签名”, 1);

SqlSession sqlSession = sqlSessionFactory.openSession();Car car = (Car)sqlSession.selectOne("org.apache.ibatis.learning.mapper.CarMapper.selectCar", 1);System.out.println(car.getName());

• 2.通过sqlSession.getMapper(CarMapper.class);获取代理对象，通过代理对象调用方法

package org.apache.ibatis.learning.mapper;
public interface CarMapper {Car selectCar(int id);
}

SqlSession sqlSession = sqlSessionFactory.openSession();
CarMapper carMapper = sqlSession.getMapper(CarMapper.class);
car = carMapper.selectCar(1);
System.out.println(car.getName());

三、源码结构

3.1 接口层

• 1.SqlSession

3.2 核心处理

• 1. 配置解析
• 2. 参数映射
• 3. sql解析
• 4. sql执行
• 5. 结果集映射
• 6. 插件

3.3 核心处理层

• 1. 数据源模块
• 2. 事务管理模块
• 3. 缓存模块
• 4. Binding模块
• 5.反射模块
• 6.类型转换模块
• 7.日志模块
• 8.资源加载
• 9.解析器模块

四、代码示例

4.1 通过inputStream构建SqlSessionFactory

package org.apache.ibatis.learning.sqlsessionfactory;import org.apache.ibatis.io.Resources;
import org.apache.ibatis.learning.mapper.Car;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.InputStream;/* @Author wangyouhui* @Description 通过inputStream构建SqlSessionFactory/
public class SqlSessionFactoryByInputStream {public static void main(String[] args) throws Exception {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();Car car = (Car)sqlSession.selectOne("org.apache.ibatis.learning.mapper.CarMapper.selectCar", 1);System.out.println(car.getName());}
}

4.2 通过configuration构建SqlSessionFactory

package org.apache.ibatis.learning.sqlsessionfactory;import org.apache.ibatis.datasource.pooled.PooledDataSource;
import org.apache.ibatis.datasource.unpooled.UnpooledDataSource;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.learning.mapper.Car;
import org.apache.ibatis.learning.mapper.CarMapper;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.apache.ibatis.transaction.TransactionFactory;
import org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;import javax.sql.DataSource;
import java.io.IOException;
import java.util.Properties;/* @Author wangyouhui* @Description 通过configuration构建SqlSessionFactory/
public class SqlSessionFactoryByConfiguration {public static void main(String[] args) throws Exception {DataSource dataSource = createDataSource();TransactionFactory transactionFactory = new JdbcTransactionFactory();Environment environment = new Environment("Production", transactionFactory, dataSource);Configuration configuration = new Configuration(environment);
//    configuration.setLazyLoadingEnabled(true);
//    configuration.setUseActualParamName(false);
//    configuration.getTypeAliasRegistry().registerAlias(Car.class);configuration.addMapper(CarMapper.class);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);SqlSession sqlSession = sqlSessionFactory.openSession();Car car = (Car)sqlSession.selectOne("org.apache.ibatis.learning.mapper.CarMapper.selectCar", 1);System.out.println(car.getName());}private static DataSource createDataSource() throws IOException {String resource = "jdbc.properties";Properties props = Resources.getResourceAsProperties(resource);PooledDataSource ds = new PooledDataSource();ds.setDriver(props.getProperty("driver"));ds.setUrl(props.getProperty("url"));ds.setUsername(props.getProperty("username"));ds.setPassword(props.getProperty("password"));ds.setDefaultAutoCommit(false);return ds;}
}

4.3 mybatis-config.xml示例

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><properties resource="jdbc.properties"/><environments default="development"><environment id="development"><transactionManager type="JDBC"></transactionManager><dataSource type="POOLED"><property name="driver" value="${driver}"/><property name="url" value="${url}"/><property name="username" value="${username}"/><property name="password" value="${password}"/></dataSource></environment></environments><mappers><mapper resource="org/apache/ibatis/learning/mapper/CarMapper.xml"></mapper></mappers>
</configuration>