mybatis源码学习笔记

￡神魔★判官ぃ 2021-09-24 15:42 451阅读 0赞

1.读取配置文件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>
        
        <properties resource="jdbc.properties"></properties>
        <typeAliases>
            <package  name="com.xqc.model" />
        </typeAliases>
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC" />
                
                <dataSource type="POOLED">
                    <property name="driver" value="${jdbc.driverClass}" />
                    <property name="url" value="${jdbc.url}" />
                    <property name="username" value="${jdbc.username}" />
                    <property name="password" value="${jdbc.password}" />
                </dataSource>
            </environment>
        </environments>
    
        <mappers>
            <mapper resource="mapper/EoStockMapper.xml" />
        </mappers>
    
    </configuration>

注意配置文件的属性顺序，不然会报错，typeAliases要写在properties猴儿面，不然会报错，例如这样写  
  
![20200905222059717.png][]  
![202009052218498.png][]读取mybatis-config.xml的方法

InputStream is = Resources.getResourceAsStream("mybatis-config.xml");

2.创建SqlSessionFactory，最为关键的步骤

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

**SqlSessionFactory的解析过程，解析**configuration的属性，  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70][]  
mybatis解析mappers文件的几种方式，官网上有4种，resource、url、class、package  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 1][]  
其中**package**优先级最高。接着是resource、url、class  
![20200905230651388.png][]  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 2][]

![20200905230824136.png][]  
3.打开SqlSession

SqlSession sqlSession = sqlSessionFactory.openSession();

mybatis的三种执行器，默认是SIMPLE  
![2020090523390227.png][]  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 3][]  
mybatis的一级缓存默认是开启的  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 4][]  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 5][]  
  
4.执行SQL

EoStockMapper eoStockMapper = sqlSession.getMapper(EoStockMapper.class);

EoStockMapper接口文件

public interface EoStockMapper {
        List<EoStockModel> selectList();
    }

EoStockMapper接口对应的xml文件

<?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="com.xqc.mapper.EoStockMapper" >
    
        <select id="selectList" resultType="EoStockModel"  useCache="false" flushCache="true">
            select
            *
            from eo_stock
        </select>
    
    </mapper>

为什么只写接口和xml就能实现查询返回结果呢？核心精髓就是jdk的动态代理

连续查询两次，第二次没有查询数据库，**（同一个SqlSession ，不同的SqlSession对象都是相互隔离的）**  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 6][]  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 7][]  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 8][]  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 9][]  
关闭一级缓存的方法：sql映射文件的配置  
![20200905235533926.png][]  
可以看到两次都查询了数据库  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 10][]  
  
EoStockMapper.xml  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RoajE5OTE4MQ_size_16_color_FFFFFF_t_70 11][]  
  
5.关闭SqlSession

sqlSession.close();

[20200905222059717.png]: /images/20210923/85824377f12a4c658eb20d08cf56f4ab.png
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