Mybatis MetaObject和ObjectWrapper設計概念

ObjectWrapper

該類的作用是對象的包裝，對對象屬性的操作，其行為有

BaseWrapper

具備了MetaObject，對象包裝的公共父類，主要處理集合類型

BeanWrapper

具備了儲存對象的Object和MetaClass

@Override
public Object get(PropertyTokenizer prop) {
    if (prop.getIndex() != null) {
        // 使用MetaObject逐級實例化集合對象
        Object collection = resolveCollection(prop, object);
        // 使用MetaObject獲得Value
        return getCollectionValue(prop, collection);
    } else {
        return getBeanProperty(prop, object);
    }
}

MetaObject

private final Object originalObject;
private final ObjectWrapper objectWrapper;
private final ObjectFactory objectFactory;
private final ObjectWrapperFactory objectWrapperFactory;
private final ReflectorFactory reflectorFactory;

private MetaObject(Object object, ObjectFactory objectFactory, ObjectWrapperFactory objectWrapperFactory, ReflectorFactory reflectorFactory) {
    this.originalObject = object;
    this.objectFactory = objectFactory;
    this.objectWrapperFactory = objectWrapperFactory;
    this.reflectorFactory = reflectorFactory;

    // 根據originalObject的類型實例化具體的ObjectMapper，將MetaObject自己注入進去，委派模式
    if (object instanceof ObjectWrapper) {
      this.objectWrapper = (ObjectWrapper) object;
    } else if (objectWrapperFactory.hasWrapperFor(object)) {
      this.objectWrapper = objectWrapperFactory.getWrapperFor(this, object);
    } else if (object instanceof Map) {
      this.objectWrapper = new MapWrapper(this, (Map) object);
    } else if (object instanceof Collection) {
      this.objectWrapper = new CollectionWrapper(this, (Collection) object);
    } else {
      this.objectWrapper = new BeanWrapper(this, object);
    }
}

獲得初始對象的屬性值通過ObjectWrapper並可能委派給MetaObject來獲得。