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/*
* Copyright 2014-2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file 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 com.amazonaws.services.dynamodbv2.document.internal;
import java.util.Iterator;
import java.util.NoSuchElementException;
import com.amazonaws.services.dynamodbv2.document.Page;
/**
* An internal iterator implementation for {@link PageBasedCollection}.
*
* NOTE: this internal class is marked as public since it has been incorrectly
* exposed in the public method {@link PageBasedCollection#iterator()}, and it
* will be changed to be package private in the next major version.
*
* @param
* resource type
* @param
* low level result type
*/
public class IteratorSupport implements Iterator {
/**
* Used to iterate through the resource pages, dynamically making network
* calls as needed.
*/
final PageIterator resourcePageIterator;
/**
* Used to iterate through a list of resources already retrieved.
*/
private Iterator localResourceIterator;
private T resource;
IteratorSupport(PageIterator resourcePageIterator) {
this.resourcePageIterator = resourcePageIterator;
}
@Override
public boolean hasNext() {
if (resource != null) {
return true;
}
resource = nextResource();
return (resource != null);
}
@Override
public T next() {
T rval = resource;
if (rval == null) {
rval = nextResource();
if (rval == null) {
throw new NoSuchElementException("No more elements");
}
} else {
resource = null;
}
return rval;
}
@Override
public void remove() {
throw new UnsupportedOperationException(
"Collection is read-only");
}
private T nextResource() {
while (true) {
if (localResourceIterator != null && localResourceIterator.hasNext()) {
return localResourceIterator.next();
}
if (!resourcePageIterator.hasNext()) {
return null;
}
Page resourcePage = resourcePageIterator.next();
localResourceIterator = resourcePage.iterator();
}
}
}