MyBatis 3源码解析(三)

三、getMapper获取接口的代理对象

1.先调用DefaultSqlSession的getMapper方法。代码如下：

  @Override
  public <T> T getMapper(Class<T> type) {
    return configuration.<T>getMapper(type, this);
  }

2.实际上是调用了configuration的getMapper方法。具体代码如下：

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

3.又是调用了mapperRegistry的getMapper方法。代码如下：

  @SuppressWarnings("unchecked")
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    // 4.根据接口类型获取mapperProxyFactory 
    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);
    }
  }

4.具体我们可以看这行：return mapperProxyFactory.newInstance(sqlSession);。mapperProxyFactory的该方法如下：

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

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