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...ce/src/eu/esdihumboldt/hale/common/instance/model/impl/FilterResourceIteratorAdapter.java
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| /* | ||
| * Copyright (c) 2024 wetransform GmbH | ||
| * | ||
| * All rights reserved. This program and the accompanying materials are made | ||
| * available under the terms of the GNU Lesser General Public License as | ||
| * published by the Free Software Foundation, either version 3 of the License, | ||
| * or (at your option) any later version. | ||
| * | ||
| * You should have received a copy of the GNU Lesser General Public License | ||
| * along with this distribution. If not, see <http://www.gnu.org/licenses/>. | ||
| * | ||
| * Contributors: | ||
| * wetransform GmbH <http://www.wetransform.to> | ||
| */ | ||
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| package eu.esdihumboldt.hale.common.instance.model.impl; | ||
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| import java.util.Iterator; | ||
| import java.util.NoSuchElementException; | ||
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| import eu.esdihumboldt.hale.common.instance.model.ResourceIterator; | ||
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| /** | ||
| * {@link ResourceIterator} adapter for a normal iterator that can perform a | ||
| * conversion from the iterator elements to a target element type. It filters | ||
| * out items that are converted to a <code>null</code> value. | ||
| * | ||
| * @param <S> the source object type served by the wrapped iterator | ||
| * @param <T> the object type served by the resource iterator | ||
| * @author Simon Templer | ||
| */ | ||
| public abstract class FilterResourceIteratorAdapter<S, T> implements ResourceIterator<T> { | ||
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| /** | ||
| * The next matching instance | ||
| */ | ||
| private T preview; | ||
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| /** | ||
| * States if the value in {@link #preview} represents a valid element | ||
| */ | ||
| private boolean previewPresent; | ||
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| /** | ||
| * States if {@link #preview}/{@link #previewPresent} must be updated | ||
| */ | ||
| private boolean updatePreview = true; | ||
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| private final Iterator<S> iterator; | ||
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| /** | ||
| * Create a {@link ResourceIterator} adapter for the given iterator. | ||
| * | ||
| * @param iterator the iterator to adapt | ||
| */ | ||
| public FilterResourceIteratorAdapter(Iterator<S> iterator) { | ||
| super(); | ||
| this.iterator = iterator; | ||
| } | ||
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| @Override | ||
| public boolean hasNext() { | ||
| update(); // ensure previewPresent/preview are set | ||
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| return previewPresent; | ||
| } | ||
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| @Override | ||
| public T next() { | ||
| update(); // ensure previewPresent/preview are set | ||
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| if (!previewPresent) { | ||
| throw new NoSuchElementException(); | ||
| } | ||
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| updatePreview = true; // next time, update the preview | ||
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| return preview; | ||
| } | ||
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| /** | ||
| * Move {@link #preview} to the next non-null converted item if possible, | ||
| * update {@link #previewPresent}. | ||
| */ | ||
| private void update() { | ||
| if (updatePreview) { | ||
| previewPresent = false; | ||
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| // find first instance matching the filter | ||
| while (!previewPresent && iterator.hasNext()) { | ||
| S item = iterator.next(); | ||
| T converted = convert(item); | ||
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| if (converted != null) { | ||
| previewPresent = true; | ||
| preview = converted; | ||
| } | ||
| } | ||
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| if (!previewPresent) { | ||
| preview = null; | ||
| } | ||
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| updatePreview = false; | ||
| } | ||
| } | ||
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| @Override | ||
| public void remove() { | ||
| throw new UnsupportedOperationException( | ||
| "Removing instances not supported on filtered collections"); | ||
| } | ||
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| /** | ||
| * Convert an object before it is returned by {@link #next()}. | ||
| * | ||
| * @param next the object to convert | ||
| * @return the converted object or null if it should be skipped | ||
| */ | ||
| protected abstract T convert(S next); | ||
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| /** | ||
| * @see ResourceIterator#close() | ||
| */ | ||
| @Override | ||
| public void close() { | ||
| if (iterator instanceof ResourceIterator<?>) { | ||
| ((ResourceIterator<?>) iterator).close(); | ||
| } | ||
| } | ||
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| } |
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