认识达内从这里开始

一. Mapper.java 创建过程

在前面注册 bean 的时候, 对beanClass 进行了替换, 为 MapperFactoryBean. 那么创建实例的时候, 会调用 MapperFactoryBean 的 getObject() 方法得到实例.

@Override

public T getObject() throws Exception {

return getSqlSession().getMapper(this.mapperInterface);

}

public SqlSession getSqlSession() {

return this.sqlSession;

}

这里的的 sqlSession 就是 前面在配置类中创建的 SqlSessionTemplate 实例.

所以 getMapper 调用的就是 SqlSessionTemplate 的 getMapper 方法. 具体调用过程有点曲折, 最后会调用 MapperRegistry 的 getMapper 方法

// SqlSessionTemplate.java

@Override

public T getMapper(Class type) {

return getConfiguration().getMapper(type, this);

}

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// Configuration.java

public T getMapper(Class type, SqlSession sqlSession) {

return mapperRegistry.getMapper(type, sqlSession);

}

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// MapperRegistry.java

public T getMapper(Class type, SqlSession sqlSession) {

final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);

if (mapperProxyFactory == null) {

throw new BindingException("Type " + type + " is not known to the MapperRegistry.");

}

try {

return mapperProxyFactory.newInstance(sqlSession);

} catch (Exception e) {

throw new BindingException("Error getting mapper instance. Cause: " + e, e);

}

}

newInstance 调用的是 MapperProxyFactory 的方法:

//MapperProxyFactory.java public T newInstance(SqlSession sqlSession) {

final MapperProxy mapperProxy = new MapperProxy(sqlSession, mapperInterface, methodCache);

return newInstance(mapperProxy);

}

protected T newInstance(MapperProxy mapperProxy) {

return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);

}

从这里可以看到, 对于 UserMapper.java 接口, 采用了 jdk代理 的方式来创建一个实例. 且代理处理类为: MapperProxy