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/*
* Copyright 2011-2012 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, 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.
* 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.amazon.carbonado.cursor;
import com.amazon.carbonado.Cursor;
import com.amazon.carbonado.FetchException;
import com.amazon.carbonado.Query;
/**
* Wraps another cursor and periodically calls a {@link com.amazon.carbonado.Query.Controller controller}.
*
* @author Brian S O'Neill
*/
public class ControllerCursor<S> extends AbstractCursor<S> {
/**
* Returns a ControllerCursor depending on whether a controller instance is
* passed in or not.
*
* @param controller optional controller which can abort query operation
* @throws IllegalArgumentException if source is null
*/
public static <S> Cursor<S> apply(Cursor<S> source, Query.Controller controller) {
return controller == null ? source : new ControllerCursor<S>(source, controller);
}
private final Cursor<S> mSource;
private final Query.Controller mController;
private byte mCount;
/**
* @param controller required controller which can abort query operation
* @throws IllegalArgumentException if either argument is null
*/
private ControllerCursor(Cursor<S> source, Query.Controller controller) {
if (source == null) {
throw new IllegalArgumentException("Source is null");
}
if (controller == null) {
throw new IllegalArgumentException("Controller is null");
}
mSource = source;
mController = controller;
controller.begin();
}
public boolean hasNext() throws FetchException {
if (mSource.hasNext()) {
continueCheck();
return true;
}
return false;
}
public S next() throws FetchException {
S next = mSource.next();
continueCheck();
return next;
}
public void close() throws FetchException {
try {
mSource.close();
} finally {
mController.close();
}
}
private void continueCheck() throws FetchException {
if (++mCount == 0) {
try {
mController.continueCheck();
} catch (FetchException e) {
try {
close();
} catch (FetchException e2) {
// Ignore.
}
throw e;
}
}
}
}
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