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

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Here is the source code for org.apache.lucene.codecs.PostingsWriterBase.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 org.apache.lucene.codecs.blocktree.BlockTreeTermsWriter;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.SegmentWriteState;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.store.IndexOutput;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.FixedBitSet;

import java.io.Closeable;
import java.io.IOException;

/**
 * Class that plugs into term dictionaries, such as {@link
 * BlockTreeTermsWriter}, and handles writing postings.
 * 
 * @see PostingsReaderBase
 * @lucene.experimental
 */
// TODO: find a better name; this defines the API that the
// terms dict impls use to talk to a postings impl.
// TermsDict + PostingsReader/WriterBase == FieldsProducer/Consumer
public abstract class PostingsWriterBase implements Closeable {

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

    /** Called once after startup, before any terms have been
     *  added.  Implementations typically write a header to
     *  the provided {@code termsOut}. */
    public abstract void init(IndexOutput termsOut, SegmentWriteState state) throws IOException;

    /** Write all postings for one term; use the provided
     *  {@link TermsEnum} to pull a {@link org.apache.lucene.index.PostingsEnum}.
     *  This method should not
     *  re-position the {@code TermsEnum}!  It is already
     *  positioned on the term that should be written.  This
     *  method must set the bit in the provided {@link
     *  FixedBitSet} for every docID written.  If no docs
     *  were written, this method should return null, and the
     *  terms dict will skip the term. */
    public abstract BlockTermState writeTerm(BytesRef term, TermsEnum termsEnum, FixedBitSet docsSeen,
            NormsProducer norms) throws IOException;

    /**
     * Encode metadata as long[] and byte[]. {@code absolute} controls whether 
     * current term is delta encoded according to latest term. 
     * Usually elements in {@code longs} are file pointers, so each one always 
     * increases when a new term is consumed. {@code out} is used to write generic
     * bytes, which are not monotonic.
     *
     * NOTE: sometimes long[] might contain "don't care" values that are unused, e.g. 
     * the pointer to postings list may not be defined for some terms but is defined
     * for others, if it is designed to inline  some postings data in term dictionary.
     * In this case, the postings writer should always use the last value, so that each
     * element in metadata long[] remains monotonic.
     */
    public abstract void encodeTerm(long[] longs, DataOutput out, FieldInfo fieldInfo, BlockTermState state,
            boolean absolute) throws IOException;

    /** 
     * Sets the current field for writing, and returns the
     * fixed length of long[] metadata (which is fixed per
     * field), called when the writing switches to another field. */
    // TODO: better name?
    public abstract int setField(FieldInfo fieldInfo);

    @Override
    public abstract void close() throws IOException;
}