common_helper/src/main/java/com/xiongyingqi/util/CompositeIterator.java
public void add(Iterator<E> iterator) {
        Assert.state(!inUse, "You can no longer add iterator to a composite iterator that's already in use");
        if (iterators.contains(iterator)) {
            throw new IllegalArgumentException("You cannot add the same iterator twice");
        }
        iterators.add(iterator);
    }
public void add(Iterator<E> iterator) {
        Assert.state(!inUse, "You can no longer add iterator to a composite iterator that's already in use");
        if (iterators.contains(iterator)) {
            throw new IllegalArgumentException("You cannot add the same iterator twice");
        }
        iterators.add(iterator);
    }
Add given iterator to this composite.