mybatis第5 章：MapperRegistry

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李延 LV6 2021-06-06

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# 作用

在那些xml和第一次加载接口的时候。都通过MapperRegistry，将Mapper进行注册。另外，MapperFactoryBean的getObject方法最终也是通过这个方法获取代理的。

# addMapper

注册服务

```java
public <T> void addMapper(Class<T> type) {
    //判断是否为接口
    if (type.isInterface()) {
      if (hasMapper(type)) {
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {
        //创建MapperProxyFactory对象，并注册
        knownMappers.put(type, new MapperProxyFactory<T>(type));
        // It's important that the type is added before the parser is run
        // otherwise the binding may automatically be attempted by the
        // mapper parser. If the type is already known, it won't try.
        //尝试解析注册
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

```

我们看到一方面创建了代理MapperProxyFactory对象，并保存在了knownMappers中，另一方面创建MapperAnnotationBuilder对象，解析注解。

# getMapper

```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);
    }
  }

```

我们看到获取代理是通过之前注册的MapperProxyFactory对象。调用newInstance方法实现

# MapperProxyFactory

```java

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);
  }

```

这里我们看到 这里使用的是java动态代理的方法。其代理对象为MapperProxy

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