/* * This file is part of the GeoLatte project. * * GeoLatte is free software: you can redistribute it and/or modify * it 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. * * GeoLatte is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public License * along with GeoLatte. If not, see <http://www.gnu.org/licenses/>. * * Copyright (C) 2010 - 2010 and Ownership of code is shared by: * Qmino bvba - Romeinsestraat 18 - 3001 Heverlee (http://www.qmino.com) * Geovise bvba - Generaal Eisenhowerlei 9 - 2140 Antwerpen (http://www.geovise.com) */ package org.geolatte.common.transformer; import java.util.Iterator; import java.util.NoSuchElementException; /** * <p> * Performs a filtering operation on its source elements. When the given filter {@link Transformation} ({@code <_, Boolean>}) evaluates * to false, the source element is not passed, when it evaluates to true, it is passed unmodified to the output. * </p> * * <pre> * input | tf | output * -------------------- * obj1 | false | - * obj2 | true | obj2 * obj3 | false | - * obj4 | true | obj4 * obj5 |*excep*| - (+ error event) * </pre> * * * <p> * <i>Creation-Date</i>: 02-Jun-2010<br> * <i>Creation-Time</i>: 17:08:21<br> * </p> * * @author Bert Vanhooff * @author <a href="http://www.qmino.com">Qmino bvba</a> * @since SDK1.5 */ public class DefaultFilter<Source> extends AbstractObservableTransformer<Source, Source> { private Transformation<Source, Boolean> filter; private Iterable<? extends Source> currentInput; // The currentInput Iterable set by the client private Iterable<Source> currentOutput; /** * Constructs a DefaultFilterTransformer which calls the given transformation. * * @param transformation Cannot be null * @throws IllegalArgumentException When transformation is null. */ public DefaultFilter(Transformation<Source, Boolean> transformation) { if (transformation == null) throw new IllegalArgumentException("Argument transformation cannot be null"); this.filter = transformation; } /** * {@inheritDoc} */ @Override protected void setInput(Iterable<? extends Source> input) { currentInput = input; currentOutput = null; } /** * {@inheritDoc} */ @Override protected Iterable<Source> output() { if (currentInput == null && currentOutput == null) return null; // In case a transformation is already in progress, return the existing output iterable if (currentOutput != null) return currentOutput; // No transformation is in progress -> create new output and forget the input currentOutput = new FilterIterable<Source>(currentInput.iterator()); currentInput = null; return currentOutput; } /* * Implementation of the actual transformer process is encapsulated in an internal Iterator. */ /** * The Iterable implementation for DefaultFilter. Returns the FilterIterator. * * @param <Source> Source type that must correspond to the Source type of the corresponding transformer. */ private class FilterIterable<Source> implements Iterable<Source> { private Iterator<? extends Source> inputIterator; private FilterIterable(Iterator<? extends Source> inputIterator) { this.inputIterator = inputIterator; } /** * Returns an iterator for the Transformer. * * @return An iterator for the Transformer. */ public Iterator<Source> iterator() { return new FilterIterator<Source>(inputIterator); } } /** * The Iterator implementation that delegates to DefaultFilter to get its next value. * * @param <T> Target type that must correspond to the Source type of the corresponding transformer. */ private class FilterIterator<T> implements Iterator<T> { private Iterator<? extends T> inputIterator; private T cachedElement = null; private boolean isCachedElementValid = false; private FilterIterator(Iterator<? extends T> inputIterator) { this.inputIterator = inputIterator; } /** * Returns <tt>true</tt> if the transformation can produce more elements. (In other * words, returns <tt>true</tt> if <tt>next</tt> would return an element * rather than throwing an exception.) * * @return <tt>true</tt> if the transformation can produce more elements. */ @SuppressWarnings("unchecked") public boolean hasNext() { if (isCachedElementValid) return true; while (inputIterator.hasNext()) { T nextElement = null; try { nextElement = inputIterator.next(); // Don't know why this cast is actually necassary if (filter.transform((Source)nextElement)) { // passed through filter cachedElement = nextElement; isCachedElementValid = true; } else { // Not passed through filter -> try the next element cachedElement = null; isCachedElementValid = false; continue; } return true; } catch (TransformationException e) { onTransformerErrorOccurred((Source)nextElement, e); } } return false; } /** * Returns the next transformed element. * * @return The next transformed element. */ public T next() { if (isCachedElementValid || hasNext()) { isCachedElementValid = false; return cachedElement; } throw new NoSuchElementException(); } /** * Not supported. */ public void remove() { throw new UnsupportedOperationException(); } } }