org.apache.lucene.search.QueryVisitor.java Source code

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Here is the source code for org.apache.lucene.search.QueryVisitor.java

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/*
 * 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.lucene.search;

import java.util.Arrays;
import java.util.Set;

import org.apache.lucene.index.Term;

/**
 * Allows recursion through a query tree
 *
 * @see Query#visit(QueryVisitor)
 */
public abstract class QueryVisitor {

    /**
     * Called by leaf queries that match on specific terms
     *
     * @param query  the leaf query
     * @param terms  the terms the query will match on
     */
    public void consumeTerms(Query query, Term... terms) {
    }

    // TODO it would be nice to have a way to consume 'classes' of Terms from
    // things like AutomatonQuery

    /**
     * Called by leaf queries that do not match on terms
     * @param query the query
     */
    public void visitLeaf(Query query) {
    }

    /**
     * Whether or not terms from this field are of interest to the visitor
     *
     * Implement this to avoid collecting terms from heavy queries such as {@link TermInSetQuery}
     * that are not running on fields of interest
     */
    public boolean acceptField(String field) {
        return true;
    }

    /**
     * Pulls a visitor instance for visiting child clauses of a query
     *
     * The default implementation returns {@code this}, unless {@code occur} is equal
     * to {@link BooleanClause.Occur#MUST_NOT} in which case it returns
     * {@link #EMPTY_VISITOR}
     *
     * @param occur   the relationship between the parent and its children
     * @param parent  the query visited
     */
    public QueryVisitor getSubVisitor(BooleanClause.Occur occur, Query parent) {
        if (occur == BooleanClause.Occur.MUST_NOT) {
            return EMPTY_VISITOR;
        }
        return this;
    }

    /**
     * Builds a {@code QueryVisitor} instance that collects all terms that may match a query
     * @param termSet a {@code Set} to add collected terms to
     */
    public static QueryVisitor termCollector(Set<Term> termSet) {
        return new QueryVisitor() {
            @Override
            public void consumeTerms(Query query, Term... terms) {
                termSet.addAll(Arrays.asList(terms));
            }
        };
    }

    /**
     * A QueryVisitor implementation that does nothing
     */
    public static final QueryVisitor EMPTY_VISITOR = new QueryVisitor() {
    };

}