org.springframework.util.CompositeIterator Maven / Gradle / Ivy
/*
* Copyright 2002-2018 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.util;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* Composite iterator that combines multiple other iterators,
* as registered via {@link #add(Iterator)}.
*
* This implementation maintains a linked set of iterators
* which are invoked in sequence until all iterators are exhausted.
*
* @author Erwin Vervaet
* @author Juergen Hoeller
* @since 3.0
* @param the element type
*/
public class CompositeIterator implements Iterator {
private final Set> iterators = new LinkedHashSet<>();
private boolean inUse = false;
/**
* Add given iterator to this composite.
*/
public void add(Iterator iterator) {
Assert.state(!this.inUse, "You can no longer add iterators to a composite iterator that's already in use");
if (this.iterators.contains(iterator)) {
throw new IllegalArgumentException("You cannot add the same iterator twice");
}
this.iterators.add(iterator);
}
@Override
public boolean hasNext() {
this.inUse = true;
for (Iterator iterator : this.iterators) {
if (iterator.hasNext()) {
return true;
}
}
return false;
}
@Override
public E next() {
this.inUse = true;
for (Iterator iterator : this.iterators) {
if (iterator.hasNext()) {
return iterator.next();
}
}
throw new NoSuchElementException("All iterators exhausted");
}
@Override
public void remove() {
throw new UnsupportedOperationException("CompositeIterator does not support remove()");
}
}