Spring ManagedList

@Override
@SuppressWarnings("unchecked")
public List<E> merge(@Nullable Object parent) {
   if (!this.mergeEnabled) {
      throw new IllegalStateException("Not allowed to merge when the 'mergeEnabled' property is set to 'false'");
   }
   if (parent == null) {
      return this;
   }
   if (!(parent instanceof List)) {
      throw new IllegalArgumentException("Cannot merge with object of type [" + parent.getClass() + "]");
   }
   // 创建对象
   List<E> merged = new ManagedList<>();
   // 放入 集合列表中
   merged.addAll((List<E>) parent);
   merged.addAll(this);
   return merged;
}