org.apache.jackrabbit.oak.security.user.query.ResultIterator Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.jackrabbit.oak.security.user.query;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* Implements a query result iterator which only returns a maximum number of
* element from an underlying iterator starting at a given offset.
*
* @param element type of the query results
*/
public final class ResultIterator implements Iterator {
public static final int OFFSET_NONE = 0;
public static final int MAX_ALL = -1;
private final Iterator iterator;
private final long offset;
private final long max;
private int pos;
private T next;
/**
* Create a new {@code ResultIterator} with a given offset and maximum
*
* @param offset Offset to start iteration at. Must be non negative
* @param max Maximum elements this iterator should return.
* Set to {@link #MAX_ALL} for all results.
* @param iterator the underlying iterator
* @throws IllegalArgumentException if offset is negative
*/
private ResultIterator(long offset, long max, Iterator iterator) {
if (offset < OFFSET_NONE) {
throw new IllegalArgumentException("Offset must not be negative");
}
this.iterator = iterator;
this.offset = offset;
this.max = max;
}
/**
* Returns an iterator respecting the specified {@code offset} and {@code max}.
*
* @param offset offset to start iteration at. Must be non negative
* @param max maximum elements this iterator should return. Set to
* {@link #MAX_ALL} for all
* @param iterator the underlying iterator
* @param element type
* @return an iterator which only returns the elements in the given bounds
*/
public static Iterator create(long offset, long max, Iterator iterator) {
if (offset == OFFSET_NONE && max == MAX_ALL) {
// no constraints on offset nor max -> return the original iterator.
return iterator;
} else {
return new ResultIterator(offset, max, iterator);
}
}
//-----------------------------------------------------------< Iterator >---
@Override
public boolean hasNext() {
if (next == null) {
fetchNext();
}
return next != null;
}
@Override
public T next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
return consumeNext();
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
//------------------------------------------------------------< private >---
private void fetchNext() {
for (; pos < offset && iterator.hasNext(); pos++) {
next = iterator.next();
}
if (pos < offset || !iterator.hasNext() || max >= 0 && pos - offset + 1 > max) {
next = null;
} else {
next = iterator.next();
pos++;
}
}
private T consumeNext() {
T element = next;
next = null;
return element;
}
}