AbstractUnaryClause.java

/* Copyright (2005-2012) Schibsted ASA
 * This file is part of Possom.
 *
 *   Possom 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.
 *
 *   Possom 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 Possom.  If not, see <http://www.gnu.org/licenses/>.
 * AbstractOperationClause.java
 *
 * Created on 7 January 2006, 16:05
 *
 */

package no.sesat.search.query.parser;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.Set;
import no.sesat.commons.ref.ReferenceMap;
import no.sesat.search.query.Clause;
import no.sesat.search.query.UnaryClause;
import no.sesat.search.query.token.TokenEvaluationEngine;
import no.sesat.search.query.token.TokenPredicate;
import org.apache.log4j.Logger;

/**
 * Basic implementation of the OperationClause interface.
 * Implements ontop of AbstractClause.
 * <b>Objects of this class are immutable</b>
 *
 *
 * @version $Id$
 */
public abstract class AbstractUnaryClause extends AbstractClause implements UnaryClause {

    private static final Logger LOG = Logger.getLogger(AbstractLeafClause.class);

    /**
     * Works off the assumption that OperationClause constructor's have the exact parameter list:
     *       final String term,
     *       final Clause left,
     *       final Clause right,
     *       final Set<Predicate> knownPredicates,
     *       final Set<Predicate> possiblePredicates
     *
     * Where this is true subclasses are free to use this helper method.
     *
     * @param left the left child clause for OperationClause the clause we are about to create (or find) will have.
     * @param right the right child clause the clause we are about to create (or find) will have.
     * @param clauseClass the exact subclass of AbstracLeafClause that we are about to create (or find already in use).
     * @param term the term the clause we are about to create (or find) will have.
     * @param engine the factory handing out evaluators against TokenPredicates.
     * Also holds state information about the current term/clause we are finding predicates against.
     * @param weakCache the map containing the key to WeakReference (of the Clause) mappings.
     * @return Either a clause already in use that matches this term and field, or a newly created cluase for this term and field.
     */
    public static <T extends AbstractUnaryClause> T createClause(
            final Class<T> clauseClass,
            final String term,
            final Clause left,
            final Clause right,
            final TokenEvaluationEngine engine,
            final ReferenceMap<String,T> weakCache) {


        final String key = term; // important that the key argument is unique to this object.

        // check weak reference cache of immutable wordClauses here.
        // no need to synchronise, no big lost if duplicate identical objects are created and added over each other
        //  into the cache, compared to the performance lost of trying to synchronise this.
        T clause = findClauseInUse(key, weakCache);

        if (clause == null) {
            // Doesn't exist in weak-reference cache. let's find the predicates and create the WordClause.

            // find the applicale predicates now
            final boolean healthy = findPredicates(engine);
            try {
                // find the constructor...
                final Constructor<T> constructor = clauseClass.getDeclaredConstructor(
                    String.class, Clause.class, Clause.class, Set.class, Set.class
                );
                // use the constructor...
                clause = constructor.newInstance(
                    term,
                    left,
                    right,
                    engine.getState().getKnownPredicates(),
                    engine.getState().getPossiblePredicates()
                );

            } catch (SecurityException ex) {
                LOG.error(ERR_FAILED_FINDING_OR_USING_CONSTRUCTOR + clauseClass.getName(), ex);
            } catch (NoSuchMethodException ex) {
                LOG.error(ERR_FAILED_FINDING_OR_USING_CONSTRUCTOR + clauseClass.getName(), ex);
            } catch (IllegalArgumentException ex) {
                LOG.error(ERR_FAILED_FINDING_OR_USING_CONSTRUCTOR + clauseClass.getName(), ex);
            } catch (InstantiationException ex) {
                LOG.error(ERR_FAILED_FINDING_OR_USING_CONSTRUCTOR + clauseClass.getName(), ex);
            } catch (InvocationTargetException ex) {
                LOG.error(ERR_FAILED_FINDING_OR_USING_CONSTRUCTOR + clauseClass.getName(), ex);
            } catch (IllegalAccessException ex) {
                LOG.error(ERR_FAILED_FINDING_OR_USING_CONSTRUCTOR + clauseClass.getName(), ex);
            }

            if( healthy ){
                return addClauseInUse(key, clause, weakCache);
            }
        }

        return clause;
    }

    /**
     * Create clause with the given term, known and possible predicates.
     * @param term the term (query string) for this clause.
     * @param first
     * @param knownPredicates the set of known predicates for this clause.
     * @param possiblePredicates the set of possible predicates for this clause.
     */
    protected AbstractUnaryClause(
            final String term,
            final Clause first,
            final Set<TokenPredicate> knownPredicates,
            final Set<TokenPredicate> possiblePredicates) {

        super(term, knownPredicates, possiblePredicates);
        firstClause = first;
    }

    /**
     *  The first clause of a binary clause, or the only clause of a UnaryClause.
     */
    protected final Clause firstClause;

    /**
     * Get the firstClause.
     *
     * @return the firstClause.
     */
    public Clause getFirstClause() {
        return firstClause;
    }

    @Override
    public String toString() {
        return getClass().getSimpleName() + '[' + getFirstClause() + ']';
    }
}