mybatis - mapper.java 的建立

一. Mapper.java 建立過程

在前面注冊 bean 的時候, 對beanClass 進行了替換, 為 MapperFactoryBean. 那麼建立執行個體的時候, 會調用 MapperFactoryBean 的 getObject() 方法得到執行個體. 

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

  public SqlSession getSqlSession() {
    return this.sqlSession;
  }      

這裡的的 sqlSession 就是 前面在配置類中建立的 SqlSessionTemplate 執行個體.

是以 getMapper 調用的就是 SqlSessionTemplate 的 getMapper 方法. 具體調用過程有點曲折, 最後會調用  MapperRegistry 的 getMapper 方法

// SqlSessionTemplate.java
  @Override
  public <T> T getMapper(Class<T> type) {
    return getConfiguration().getMapper(type, this);
  }

 |
 |
\|/
 
  // Configuration.java
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
  }

 |
 |
\|/

  // MapperRegistry.java
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) 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 調用的是  MapperProxyFactory 的方法:

//MapperProxyFactory.java
  public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }


  protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }      

從這裡可以看到, 對于 UserMapper.java 接口, 采用了 jdk代理 的方式來建立一個執行個體. 且代理處理類為:  MapperProxy