mybatis源码分析

mybatis 一般集成到spring框架中使用，下面介绍如何在spring中使用mybatis

1. 创建datasource实例

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName">
            <value>com.mysql.jdbc.Driver</value>
        </property>
        <property name="url">
            <value>jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8</value>
   
        </property>
        <property name="username">
            <value>root</value>
        </property>
        <property name="password">
            <value>xxx</value>
        </property>
    </bean>

2. 创建SqlSessionFactoryBean 实例

    <bean id="sqlSession" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
        <property name="plugins">
            <array>
                <bean class="com.learn.springmybatis.ExecutorInterceptor"></bean>
            </array>
        </property>
    </bean>

3. 创建数据库操作的bean

    <bean id="userDao" class="org.mybatis.spring.mapper.MapperFactoryBean">
        <property name="mapperInterface" value="com.learn.springmybatis.UserDao"/>
        <property name="sqlSessionFactory" ref="sqlSession"></property>
    </bean>

   当然还有具体java代码，这里不体现出来。列出上述配置主要说明mybatis使用的大体流程。业务代码最终是拿数据库操作bean实例，如userDao去操作数据库。那我们就从userDao开始吧，看看业务代码通过mybatis是如何和db打交道的。

userDao的实例化过程

下面是UserDao的java代码，一个Interface，里面除了有一个注解，啥都没有。那么它是如何实现数据插入的呢？

public interface UserDao {

    @Insert(" insert into user ( id, name, title ) values (#{id},#{name}, #{title}) ")
    public int insert(User user);
}

• userDao是MapperFactoryBean创建的
  从xml配置我们可以得知，userDao是MapperFactoryBean创建，而MapperFactoryBean实现类FactoryBean接口，Spring的FactoryBean可以根据需要创建不同类型的bean

  通过MapperFactoryBean的getObject获取userDao实例

    public T getObject() throws Exception {
        return this.getSqlSession().getMapper(this.mapperInterface);
    }

  this.getSqlSession()是new SqlSessionTemplate(sqlSessionFactory)
  最终进入Configuration的getMapper

    public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        return this.mapperRegistry.getMapper(type, sqlSession);
    }

  最终调用到MapperRegistry，具体代码如下，通过type在knownMappers获取mapperProxyFactory，这里直接用knownMappers，那么这个knownMapper什么时候初始化好的？先留个疑问，不着急解答。获取到mapperProxyFactory后创建新的实例

    public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);
        if (mapperProxyFactory == null) {
            throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
        } else {
            try {
                return mapperProxyFactory.newInstance(sqlSession);
            } catch (Exception var5) {
                throw new BindingException("Error getting mapper instance. Cause: " + var5, var5);
            }
        }
    }

  新实例如何创建？看代码，用到java的动态代理,sql的执行，最终会代理到这个MapperProxy进行，想知道sql如何执行，只需分析MapperProxy即可。

    protected T newInstance(MapperProxy<T> mapperProxy) {
        return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy);
    }
  
    public T newInstance(SqlSession sqlSession) {
        MapperProxy<T> mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);
        return this.newInstance(mapperProxy);
    }

• 未完待续