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

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Here is the source code for org.apache.lucene.search.RegexpQuery.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 org.apache.lucene.index.Term;
import org.apache.lucene.util.automaton.Automaton;
import org.apache.lucene.util.automaton.AutomatonProvider;
import org.apache.lucene.util.automaton.Operations;
import org.apache.lucene.util.automaton.RegExp;

/**
 * A fast regular expression query based on the
 * {@link org.apache.lucene.util.automaton} package.
 * <ul>
 * <li>Comparisons are <a
 * href="http://tusker.org/regex/regex_benchmark.html">fast</a>
 * <li>The term dictionary is enumerated in an intelligent way, to avoid
 * comparisons. See {@link AutomatonQuery} for more details.
 * </ul>
 * <p>
 * The supported syntax is documented in the {@link RegExp} class.
 * Note this might be different than other regular expression implementations.
 * For some alternatives with different syntax, look under the sandbox.
 * </p>
 * <p>
 * Note this query can be slow, as it needs to iterate over many terms. In order
 * to prevent extremely slow RegexpQueries, a Regexp term should not start with
 * the expression <code>.*</code>
 * 
 * @see RegExp
 * @lucene.experimental
 */
public class RegexpQuery extends AutomatonQuery {
    /**
     * A provider that provides no named automata
     */
    private static AutomatonProvider defaultProvider = new AutomatonProvider() {
        @Override
        public Automaton getAutomaton(String name) {
            return null;
        }
    };

    /**
     * Constructs a query for terms matching <code>term</code>.
     * <p>
     * By default, all regular expression features are enabled.
     * </p>
     * 
     * @param term regular expression.
     */
    public RegexpQuery(Term term) {
        this(term, RegExp.ALL);
    }

    /**
     * Constructs a query for terms matching <code>term</code>.
     * 
     * @param term regular expression.
     * @param flags optional RegExp features from {@link RegExp}
     */
    public RegexpQuery(Term term, int flags) {
        this(term, flags, defaultProvider, Operations.DEFAULT_MAX_DETERMINIZED_STATES);
    }

    /**
     * Constructs a query for terms matching <code>term</code>.
     * 
     * @param term regular expression.
     * @param flags optional RegExp features from {@link RegExp}
     * @param maxDeterminizedStates maximum number of states that compiling the
     *  automaton for the regexp can result in.  Set higher to allow more complex
     *  queries and lower to prevent memory exhaustion.
     */
    public RegexpQuery(Term term, int flags, int maxDeterminizedStates) {
        this(term, flags, defaultProvider, maxDeterminizedStates);
    }

    /**
     * Constructs a query for terms matching <code>term</code>.
     * 
     * @param term regular expression.
     * @param flags optional RegExp features from {@link RegExp}
     * @param provider custom AutomatonProvider for named automata
     * @param maxDeterminizedStates maximum number of states that compiling the
     *  automaton for the regexp can result in.  Set higher to allow more complex
     *  queries and lower to prevent memory exhaustion.
     */
    public RegexpQuery(Term term, int flags, AutomatonProvider provider, int maxDeterminizedStates) {
        super(term, new RegExp(term.text(), flags).toAutomaton(provider, maxDeterminizedStates),
                maxDeterminizedStates);
    }

    /** Returns the regexp of this query wrapped in a Term. */
    public Term getRegexp() {
        return term;
    }

    /** Prints a user-readable version of this query. */
    @Override
    public String toString(String field) {
        StringBuilder buffer = new StringBuilder();
        if (!term.field().equals(field)) {
            buffer.append(term.field());
            buffer.append(":");
        }
        buffer.append('/');
        buffer.append(term.text());
        buffer.append('/');
        return buffer.toString();
    }
}