| /******************************************************************************* |
| * Copyright (c) 2009, 2010 EclipseSource and others. All rights reserved. This |
| * program and the accompanying materials are made available under the terms of |
| * the Eclipse Public License v1.0 which accompanies this distribution, and is |
| * available at http://www.eclipse.org/legal/epl-v10.html |
| * |
| * Contributors: |
| * EclipseSource - initial API and implementation |
| * IBM Corporation - ongoing development |
| ******************************************************************************/ |
| package org.eclipse.equinox.p2.query; |
| |
| import java.util.Iterator; |
| import org.eclipse.equinox.p2.metadata.expression.IExpression; |
| |
| /** |
| * This class represents a simple Java-based query. Clients may subclass and |
| * override the {@link #isMatch(Object)} method in order to write simple |
| * queries against p2 metadata. |
| * <p> |
| * Note that hand-written queries cannot be optimized for queryables containing |
| * indices, or for remote queryables. In general you should use one of the pre-defined |
| * queries found in {@link QueryUtil} if possible, to obtain queries optimized for indexing and |
| * remote execution. This class is intended for simple queries against small data |
| * sources where indexed lookup and remote query execution are not needed. |
| * </p> |
| * @since 2.0 |
| */ |
| public abstract class MatchQuery<T> implements IMatchQuery<T> { |
| |
| /** |
| * Returns whether the given object satisfies the parameters of this query. |
| * |
| * @param candidate The object to perform the query against |
| * @return <code>true</code> if the unit satisfies the parameters |
| * of this query, and <code>false</code> otherwise |
| * |
| * @noreference This method is not intended to be referenced by clients. |
| * Clients should call {@link #perform(Iterator)} |
| */ |
| public abstract boolean isMatch(T candidate); |
| |
| /** |
| * Performs this query on the given iterator, passing all objects in the iterator |
| * that match the criteria of this query to the given result. |
| */ |
| public final IQueryResult<T> perform(Iterator<T> iterator) { |
| Collector<T> result = new Collector<T>(); |
| while (iterator.hasNext()) { |
| T candidate = iterator.next(); |
| if (candidate != null && isMatch(candidate)) |
| if (!result.accept(candidate)) |
| break; |
| } |
| return result; |
| } |
| |
| /** |
| * Execute any pre-processing that must be done before this query is performed against |
| * a particular iterator. This method may be used by subclasses to do any calculations, |
| * caching, or other preparation for the query. |
| * <p> |
| * This method is internal to the framework. Subclasses may override this method, but |
| * should not call this method. |
| * |
| * @noreference This method is not intended to be referenced by clients. |
| */ |
| public void prePerform() { |
| // nothing to do by default |
| } |
| |
| /** |
| * Execute any post-processing that must be done after this query has been performed against |
| * a particular iterator. This method may be used by subclasses to clear caches or any other |
| * cleanup that should occur after a query. |
| * <p> |
| * This method will be called even if the query does not complete successfully. |
| * <p> |
| * This method is internal to the framework. Subclasses may override this method, but |
| * should not call this method. |
| * |
| * @noreference This method is not intended to be referenced by clients. |
| */ |
| public void postPerform() { |
| // nothing to do by default |
| } |
| |
| public IExpression getExpression() { |
| return null; |
| } |
| } |