sharedfieldsortcomparator.java

来自「jsr170接口的java实现。是个apache的开源项目。」· Java 代码 · 共 142 行

/*
 * 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.jackrabbit.core.query.lucene;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.FieldCache;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.ScoreDocComparator;
import org.apache.lucene.search.SortComparator;
import org.apache.lucene.search.SortField;

import java.io.IOException;

/**
 * Implements a <code>SortComparator</code> which knows how to sort on a lucene
 * field that contains values for multiple properties.
 * <p/>
 * <b>Important:</b> The ScoreDocComparator returned by {@link #newComparator}
 * does not implement the contract for {@link ScoreDocComparator#sortValue(ScoreDoc)}
 * properly. The method will always return an empty String to save memory consumption
 * on large property ranges. Those values are only of relevance when queries
 * are executed with a <code>MultiSearcher</code>, which is currently not the
 * case in Jackrabbit.
 */
public class SharedFieldSortComparator extends SortComparator {

    /**
     * A <code>SharedFieldSortComparator</code> that is based on
     * {@link FieldNames#PROPERTIES}.
     */
    static final SortComparator PROPERTIES = new SharedFieldSortComparator(FieldNames.PROPERTIES);

    /**
     * The name of the shared field in the lucene index.
     */
    private final String field;

    /**
     * If <code>true</code> <code>ScoreDocComparator</code> will returns term
     * values when {@link org.apache.lucene.search.ScoreDocComparator#sortValue(org.apache.lucene.search.ScoreDoc)}
     * is called, otherwise only a dummy value is returned.
     */
    private final boolean createComparatorValues;

    /**
     * Creates a new <code>SharedFieldSortComparator</code> for a given shared
     * field.
     *
     * @param fieldname the shared field.
     */
    public SharedFieldSortComparator(String fieldname) {
        this(fieldname, false);
    }

    /**
     * Creates a new <code>SharedFieldSortComparator</code> for a given shared
     * field.
     *
     * @param fieldname              the shared field.
     * @param createComparatorValues if <code>true</code> creates values
     * for the <code>ScoreDocComparator</code>s.
     * @see #createComparatorValues
     */
    public SharedFieldSortComparator(String fieldname, boolean createComparatorValues) {
        this.field = fieldname;
        this.createComparatorValues = createComparatorValues;
    }

    /**
     * Creates a new <code>ScoreDocComparator</code> for an embedded
     * <code>propertyName</code> and a <code>reader</code>.
     * @param reader the index reader.
     * @param propertyName the name of the property to sort.
     * @return a <code>ScoreDocComparator</code> for the
     * @throws IOException
     */
    public ScoreDocComparator newComparator(final IndexReader reader, String propertyName)
            throws IOException {
        // get the StringIndex for propertyName
        final FieldCache.StringIndex index
                = SharedFieldCache.INSTANCE.getStringIndex(reader, field,
                        FieldNames.createNamedValue(propertyName, ""),
                        SharedFieldSortComparator.this,
                        createComparatorValues);

        return new ScoreDocComparator() {
            public final int compare(final ScoreDoc i, final ScoreDoc j) {
                final int fi = index.order[i.doc];
                final int fj = index.order[j.doc];
                if (fi < fj) {
                    return -1;
                } else if (fi > fj) {
                    return 1;
                } else {
                    return 0;
                }
            }

            /**
             * Returns an empty if no lookup table is available otherwise
             * the index term for the score doc <code>i</code>.
             *
             * @param i the score doc.
             * @return the sort value if available.
             */
            public Comparable sortValue(final ScoreDoc i) {
                if (index.lookup != null) {
                    return index.lookup[index.order[i.doc]];
                } else {
                    // return dummy value
                    return "";
                }
            }

            public int sortType() {
                return SortField.CUSTOM;
            }
        };
    }

    /**
     * @throws UnsupportedOperationException always.
     */
    protected Comparable getComparable(String termtext) {
        throw new UnsupportedOperationException();
    }
}