Mybatis接口编程原理分析（三）

前面两篇博客​​Mybatis接口编程原理分析（一）​​​和​​Mybatis接口编程原理分析（二）​​我们介绍了MapperProxyFactory、MapperProxy和MapperMethod的操作及源码分析，接下来我们介绍MapperRegistry

MapperRegistry：它是用来注册Mapper接口和获取登出代理类实例的工具类，它通过getMapper函数获得代理类和addMapper函数来注册代理类，

源码如下：

 

//这个类通过名字就可以看出 是用来注册Mapper接口与获取生成代理类实例的工具类
public class MapperRegistry {
  
  //全局配置文件对象
  private final Configuration config;
  
  //一个HashMap Key是mapper的类型对象, Value是MapperProxyFactory对象
  //这个MapperProxyFactory是创建Mapper代理对象的工厂 
  private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>();

  public MapperRegistry(Configuration config) {
    this.config = config;
  }
   //获取生成的代理对象
  @SuppressWarnings("unchecked")
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
  //通过Mapper的接口类型 去Map当中查找 如果为空就抛异常
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
    //否则创建一个当前接口的代理对象 并且传入sqlSession
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }
  
  public <T> boolean hasMapper(Class<T> type) {
    return knownMappers.containsKey(type);
  }
  //注册Mapper接口
  public <T> void addMapper(Class<T> type) {
    if (type.isInterface()) {
      if (hasMapper(type)) {
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {
        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.
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

  /**
   * @since 3.2.2
   */
  public Collection<Class<?>> getMappers() {
    return Collections.unmodifiableCollection(knownMappers.keySet());
  }

  /**
   * @since 3.2.2
   */
  //注册Mapper接口
  public void addMappers(String packageName, Class<?> superType) {
    ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
    resolverUtil.find(new ResolverUtil.IsA(superType), packageName);
    Set<Class<? extends Class<?>>> mapperSet = resolverUtil.getClasses();
    for (Class<?> mapperClass : mapperSet) {
      addMapper(mapperClass);
    }
  }

  /**
   * @since 3.2.2
   */
  //通过包名扫描下面所有接口
  public void addMappers(String packageName) {
    addMappers(packageName, Object.class);
  }
  
}

在解析mapper.xml时会根据namespace来加载对应的接口类

private void bindMapperForNamespace() {
        //获取namespace
        String namespace = this.builderAssistant.getCurrentNamespace();
        if (namespace != null) {
            Class boundType = null;

            try {
                //判断namespace是否是一个接口
                boundType = Resources.classForName(namespace);
            } catch (ClassNotFoundException var4) {
                ;
            }

            //如果存在接口类在调用addMapper
            if (boundType != null && !this.configuration.hasMapper(boundType)) {
                this.configuration.addLoadedResource("namespace:" + namespace);
                this.configuration.addMapper(boundType);
            }
        }

    }

在DefaultSqlSession中通过getMapper函数从Configuration中获取代理类：

 

 

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

 

 

在Configuration类中通过getMapper从MapperRegistry来获取代理类

 

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

这样就完成了mybatis接口编程的构造和调用的全部过程。