/***********************************************************************************************************************
* Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
*
* 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 eu.stratosphere.pact.runtime.util;
import java.io.IOException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import eu.stratosphere.api.common.typeutils.TypeComparator;
import eu.stratosphere.api.common.typeutils.TypeSerializer;
import eu.stratosphere.util.MutableObjectIterator;
/**
* The KeyValueIterator returns a key and all values that belong to the key (share the same key).
*
*/
public final class KeyGroupedIterator<E> {
private final MutableObjectIterator<E> iterator;
private final TypeSerializer<E> serializer;
private final TypeComparator<E> comparator;
private E current;
private E lookahead;
private ValuesIterator valuesIterator;
private boolean lookAheadHasNext;
private boolean done;
/**
* Initializes the KeyGroupedIterator. It requires an iterator which returns its result
* sorted by the key fields.
*
* @param iterator An iterator over records, which are sorted by the key fields, in any order.
* @param serializer The serializer for the data type iterated over.
* @param comparator The comparator for the data type iterated over.
*/
public KeyGroupedIterator(MutableObjectIterator<E> iterator,
TypeSerializer<E> serializer, TypeComparator<E> comparator)
{
if (iterator == null || serializer == null || comparator == null) {
throw new NullPointerException();
}
this.iterator = iterator;
this.serializer = serializer;
this.comparator = comparator;
}
/**
* Moves the iterator to the next key. This method may skip any values that have not yet been returned by the
* iterator created by the {@link #getValues()} method. Hence, if called multiple times it "removes" pairs.
*
* @return true if the input iterator has an other group of key-value pairs that share the same key.
*/
public boolean nextKey() throws IOException
{
// first element (or empty)
if (this.current == null) {
if (this.done) {
this.valuesIterator = null;
return false;
}
this.current = this.serializer.createInstance();
if ((this.current = this.iterator.next(this.current)) != null) {
this.comparator.setReference(this.current);
this.lookAheadHasNext = false;
this.valuesIterator = new ValuesIterator();
this.valuesIterator.currentIsUnconsumed = true;
return true;
} else {
// empty input, set everything null
this.valuesIterator = null;
this.current = null;
this.done = true;
return false;
}
}
// Whole value-iterator was read and a new key is available.
if (this.lookAheadHasNext) {
this.lookAheadHasNext = false;
this.current = this.lookahead;
this.lookahead = null;
this.comparator.setReference(this.current);
this.valuesIterator.currentIsUnconsumed = true;
return true;
}
// try to move to next key.
// Required if user code / reduce() method did not read the whole value iterator.
while (true) {
if (!this.done && ((this.current = this.iterator.next(this.current)) != null)) {
if (!this.comparator.equalToReference(this.current)) {
// the keys do not match, so we have a new group. store the current keys
this.comparator.setReference(this.current);
this.lookAheadHasNext = false;
this.valuesIterator.currentIsUnconsumed = true;
return true;
}
}
else {
this.valuesIterator = null;
this.current = null;
this.done = true;
return false;
}
}
}
public TypeComparator<E> getComparatorWithCurrentReference() {
return this.comparator;
}
public E getCurrent() {
return this.current;
}
/**
* Returns an iterator over all values that belong to the current key. The iterator is initially <code>null</code>
* (before the first call to {@link #nextKey()} and after all keys are consumed. In general, this method returns
* always a non-null value, if a previous call to {@link #nextKey()} return <code>true</code>.
*
* @return Iterator over all values that belong to the current key.
*/
public ValuesIterator getValues() {
return this.valuesIterator;
}
// --------------------------------------------------------------------------------------------
public final class ValuesIterator implements Iterator<E>
{
private final TypeSerializer<E> serializer = KeyGroupedIterator.this.serializer;
private final TypeComparator<E> comparator = KeyGroupedIterator.this.comparator;
private E staging = this.serializer.createInstance();
private boolean currentIsUnconsumed = false;
private ValuesIterator() {}
@Override
public boolean hasNext()
{
if (KeyGroupedIterator.this.current == null || KeyGroupedIterator.this.lookAheadHasNext) {
return false;
}
if (this.currentIsUnconsumed) {
return true;
}
try {
// read the next value into the staging record to make sure we keep the
// current as it is in case the key changed
E stagingStaging = KeyGroupedIterator.this.iterator.next(this.staging);
if (stagingStaging != null) {
this.staging = stagingStaging;
if (this.comparator.equalToReference(this.staging)) {
// same key, next value is in staging, so exchange staging with current
final E tmp = this.staging;
this.staging = KeyGroupedIterator.this.current;
KeyGroupedIterator.this.current = tmp;
this.currentIsUnconsumed = true;
return true;
} else {
// moved to the next key, no more values here
KeyGroupedIterator.this.lookAheadHasNext = true;
KeyGroupedIterator.this.lookahead = this.staging;
this.staging = KeyGroupedIterator.this.current;
return false;
}
}
else {
// backing iterator is consumed
KeyGroupedIterator.this.done = true;
return false;
}
}
catch (IOException ioex) {
throw new RuntimeException("An error occurred while reading the next record: " +
ioex.getMessage(), ioex);
}
}
/**
* Prior to call this method, call hasNext() once!
*/
@Override
public E next() {
if (this.currentIsUnconsumed || hasNext()) {
this.currentIsUnconsumed = false;
return KeyGroupedIterator.this.current;
} else {
throw new NoSuchElementException();
}
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
}