org.apache.lucene.codecs.FieldsConsumer.java Source code

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Here is the source code for org.apache.lucene.codecs.FieldsConsumer.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.codecs;

import java.io.Closeable;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.lucene.index.Fields;
import org.apache.lucene.index.MappedMultiFields;
import org.apache.lucene.index.MergeState;
import org.apache.lucene.index.MultiFields;
import org.apache.lucene.index.ReaderSlice;

/** 
 * Abstract API that consumes terms, doc, freq, prox, offset and
 * payloads postings.  Concrete implementations of this
 * actually do "something" with the postings (write it into
 * the index in a specific format).
 *
 * @lucene.experimental
 */

public abstract class FieldsConsumer implements Closeable {

    /** Sole constructor. (For invocation by subclass 
     *  constructors, typically implicit.) */
    protected FieldsConsumer() {
    }

    // TODO: can we somehow compute stats for you...?

    // TODO: maybe we should factor out "limited" (only
    // iterables, no counts/stats) base classes from
    // Fields/Terms/Docs/AndPositions?

    /** Write all fields, terms and postings.  This the "pull"
     *  API, allowing you to iterate more than once over the
     *  postings, somewhat analogous to using a DOM API to
     *  traverse an XML tree.
     *
     *  <p><b>Notes</b>:
     *
     *  <ul>
     *    <li> You must compute index statistics,
     *         including each Term's docFreq and totalTermFreq,
     *         as well as the summary sumTotalTermFreq,
     *         sumTotalDocFreq and docCount.
     *
     *    <li> You must skip terms that have no docs and
     *         fields that have no terms, even though the provided
     *         Fields API will expose them; this typically
     *         requires lazily writing the field or term until
     *         you've actually seen the first term or
     *         document.
     *
     *    <li> The provided Fields instance is limited: you
     *         cannot call any methods that return
     *         statistics/counts; you cannot pass a non-null
     *         live docs when pulling docs/positions enums.
     *  </ul>
     */
    public abstract void write(Fields fields, NormsProducer norms) throws IOException;

    /** Merges in the fields from the readers in 
     *  <code>mergeState</code>. The default implementation skips
     *  and maps around deleted documents, and calls {@link #write(Fields,NormsProducer)}.
     *  Implementations can override this method for more sophisticated
     *  merging (bulk-byte copying, etc). */
    public void merge(MergeState mergeState, NormsProducer norms) throws IOException {
        final List<Fields> fields = new ArrayList<>();
        final List<ReaderSlice> slices = new ArrayList<>();

        int docBase = 0;

        for (int readerIndex = 0; readerIndex < mergeState.fieldsProducers.length; readerIndex++) {
            final FieldsProducer f = mergeState.fieldsProducers[readerIndex];

            final int maxDoc = mergeState.maxDocs[readerIndex];
            f.checkIntegrity();
            slices.add(new ReaderSlice(docBase, maxDoc, readerIndex));
            fields.add(f);
            docBase += maxDoc;
        }

        Fields mergedFields = new MappedMultiFields(mergeState,
                new MultiFields(fields.toArray(Fields.EMPTY_ARRAY), slices.toArray(ReaderSlice.EMPTY_ARRAY)));
        write(mergedFields, norms);
    }

    // NOTE: strange but necessary so javadocs linting is happy:
    @Override
    public abstract void close() throws IOException;
}