DownloadIterator.java

/*
 * Copyright 2014 Google Inc. 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.
 * 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 com.google.identitytoolkit;

import com.google.common.collect.ImmutableSet;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Iterator which supports paginated download.
 *
 * @param <T> Element type
 */
public abstract class DownloadIterator<T> implements Iterator<T> {

  private Iterator<T> iterator = ImmutableSet.<T>of().iterator();

  protected abstract Iterator<T> getNextResults();

  @Override
  public boolean hasNext() {
    if (!iterator.hasNext()) {
      iterator = getNextResults();
    }
    return iterator.hasNext();
  }

  @Override
  public T next() {
    if (hasNext()) {
      return iterator.next();
    } else {
      throw new NoSuchElementException();
    }
  }

  @Override
  public void remove() {
    throw new UnsupportedOperationException();
  }
}