org.apache.lucene.index.IndexCommit.java Source code

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Here is the source code for org.apache.lucene.index.IndexCommit.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.index;

import java.util.Collection;
import java.util.Map;
import java.io.IOException;

import org.apache.lucene.store.Directory;

/**
 * <p>Expert: represents a single commit into an index as seen by the
 * {@link IndexDeletionPolicy} or {@link IndexReader}.</p>
 *
 * <p> Changes to the content of an index are made visible
 * only after the writer who made that change commits by
 * writing a new segments file
 * (<code>segments_N</code>). This point in time, when the
 * action of writing of a new segments file to the directory
 * is completed, is an index commit.</p>
 *
 * <p>Each index commit point has a unique segments file
 * associated with it. The segments file associated with a
 * later index commit point would have a larger N.</p>
 *
 * @lucene.experimental
*/

// TODO: this is now a poor name, because this class also represents a
// point-in-time view from an NRT reader
public abstract class IndexCommit implements Comparable<IndexCommit> {

    /**
     * Get the segments file (<code>segments_N</code>) associated 
     * with this commit point.
     */
    public abstract String getSegmentsFileName();

    /**
     * Returns all index files referenced by this commit point.
     */
    public abstract Collection<String> getFileNames() throws IOException;

    /**
     * Returns the {@link Directory} for the index.
     */
    public abstract Directory getDirectory();

    /**
     * Delete this commit point.  This only applies when using
     * the commit point in the context of IndexWriter's
     * IndexDeletionPolicy.
     * <p>
     * Upon calling this, the writer is notified that this commit 
     * point should be deleted. 
     * <p>
     * Decision that a commit-point should be deleted is taken by the {@link IndexDeletionPolicy} in effect
     * and therefore this should only be called by its {@link IndexDeletionPolicy#onInit onInit()} or 
     * {@link IndexDeletionPolicy#onCommit onCommit()} methods.
    */
    public abstract void delete();

    /** Returns true if this commit should be deleted; this is
     *  only used by {@link IndexWriter} after invoking the
     *  {@link IndexDeletionPolicy}. */
    public abstract boolean isDeleted();

    /** Returns number of segments referenced by this commit. */
    public abstract int getSegmentCount();

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

    /** Two IndexCommits are equal if both their Directory and versions are equal. */
    @Override
    public boolean equals(Object other) {
        if (other instanceof IndexCommit) {
            IndexCommit otherCommit = (IndexCommit) other;
            return otherCommit.getDirectory() == getDirectory() && otherCommit.getGeneration() == getGeneration();
        } else {
            return false;
        }
    }

    @Override
    public int hashCode() {
        return getDirectory().hashCode() + Long.valueOf(getGeneration()).hashCode();
    }

    /** Returns the generation (the _N in segments_N) for this
     *  IndexCommit */
    public abstract long getGeneration();

    /** Returns userData, previously passed to {@link
     *  IndexWriter#setLiveCommitData(Iterable)} for this commit.  Map is
     *  {@code String -> String}. */
    public abstract Map<String, String> getUserData() throws IOException;

    @Override
    public int compareTo(IndexCommit commit) {
        if (getDirectory() != commit.getDirectory()) {
            throw new UnsupportedOperationException(
                    "cannot compare IndexCommits from different Directory instances");
        }

        long gen = getGeneration();
        long comgen = commit.getGeneration();
        return Long.compare(gen, comgen);
    }

    /** Package-private API for IndexWriter to init from a commit-point pulled from an NRT or non-NRT reader. */
    StandardDirectoryReader getReader() {
        return null;
    }
}