org.eclipse.equinox.p2.query.MatchQuery Maven / Gradle / Ivy
/*******************************************************************************
* 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.
*
* 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.
*
* @deprecated If possible, use one of the predefined queries in {@link QueryUtil}
* or use the {@link QueryUtil#createMatchQuery(String, Object...)}
* to create a custom expression based query. If the query cannot be expressed using
* the p2QL, then use a predefined or custom expression query as a first filter
* (in worst case, use {@link QueryUtil#createIUAnyQuery()}) and then provide further filtering
* like so:
* for(iter = queryable.query(someExpressionQuery).iterator(); iter.hasNext();) {
* // do your match here
* }
* @since 2.0
*/
public abstract class MatchQuery implements IMatchQuery {
/**
* Returns whether the given object satisfies the parameters of this query.
*
* @param candidate The object to perform the query against
* @return true if the unit satisfies the parameters
* of this query, and false otherwise
*
* @noreference This method is not intended to be referenced by clients.
* Clients should call {@link #perform(Iterator)}
* @since 2.0
*/
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 perform(Iterator iterator) {
Collector result = new Collector();
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.
*
* 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.
*
* This method will be called even if the query does not complete successfully.
*
* 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;
}
}