/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.jena.reasoner;
import org.apache.jena.graph.Triple ;
import org.apache.jena.util.iterator.* ;
/**
* Some simple helper methods used when working with Finders,
* particularly to compose them into cascade sequences.
* The cascades are designed to cope with null Finders as well.
*/
public class FinderUtil {
/**
* Create a continuation object which is a cascade of two
* continuation objects.
* @param first the first Graph/Finder to try
* @param second the second Graph/Finder to try
*/
public static Finder cascade(Finder first, Finder second) {
if (first == null || (first instanceof FGraph && ((FGraph)first).getGraph() == null)) return second;
if (second == null || (second instanceof FGraph && ((FGraph)second).getGraph() == null)) return first;
return new Cascade(first, second);
}
/**
* Create a continuation object which is a cascade of three
* continuation objects.
* @param first the first Graph/Finder to try
* @param second the second Graph/Finder to try
* @param third the third Graph/Finder to try
*/
public static Finder cascade(Finder first, Finder second, Finder third) {
return new Cascade(first, cascade(second, third));
}
/**
* Create a continuation object which is a cascade of four
* continuation objects.
* @param first the first Graph/Finder to try
* @param second the second Graph/Finder to try
* @param third the third Graph/Finder to try
* @param fourth the third Graph/Finder to try
*/
public static Finder cascade(Finder first, Finder second, Finder third, Finder fourth) {
return new Cascade(first, cascade(second, cascade(third, fourth)));
}
/**
* Inner class used to implement cascades of two continuation objects
*/
private static class Cascade implements Finder {
/** the first Graph/Finder to try */
Finder first;
/** the second Graph/Finder to try */
Finder second;
/**
* Constructor
*/
Cascade(Finder first, Finder second) {
this.first = first;
this.second = second;
}
/**
* Basic pattern lookup interface.
* @param pattern a TriplePattern to be matched against the data
* @return a ClosableIterator over all Triples in the data set
* that match the pattern
*/
@Override
public ExtendedIterator<Triple> find(TriplePattern pattern) {
if (second == null) {
return first.find(pattern);
} else if (first == null) {
return second.find(pattern);
} else {
return first.findWithContinuation(pattern, second);
}
}
/**
* Extended find interface used in situations where the implementator
* may or may not be able to answer the complete query. It will
* attempt to answer the pattern but if its answers are not known
* to be complete then it will also pass the request on to the nested
* Finder to append more results.
* @param pattern a TriplePattern to be matched against the data
* @param continuation either a Finder or a normal Graph which
* will be asked for additional match results if the implementor
* may not have completely satisfied the query.
*/
@Override
public ExtendedIterator<Triple> findWithContinuation(TriplePattern pattern, Finder continuation) {
return (FinderUtil.cascade(first, second, continuation)).find(pattern);
}
/**
* Return true if the given pattern occurs somewhere in the find sequence.
*/
@Override
public boolean contains(TriplePattern pattern) {
ClosableIterator<Triple> it = find(pattern);
boolean result = it.hasNext();
it.close();
return result;
}
}
}