/*
* Copyright 2002-2014 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
*
* http://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)}.
*
* <p>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
*/
public class
CompositeIterator<E> implements
Iterator<E> {
private final
Set<
Iterator<E>>
iterators = new
LinkedHashSet<
Iterator<E>>();
private boolean
inUse = false;
/**
* Add given iterator to this composite.
*/
public void
add(
Iterator<E>
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<E>
iterator : this.
iterators) {
if (
iterator.
hasNext()) {
return true;
}
}
return false;
}
@
Override
public E
next() {
this.
inUse = true;
for (
Iterator<E>
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()");
}
}