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Lucene example source code file (IndexDeletionPolicy.java)

This example Lucene source code file (IndexDeletionPolicy.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

indexcommit, indexcommit, indexdeletionpolicy, indexdeletionpolicy, io, ioexception, ioexception, util

The Lucene IndexDeletionPolicy.java source code

package org.apache.lucene.index;

/**
 * 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.
 */

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

/**
 * <p>Expert: policy for deletion of stale {@link IndexCommit index commits}. 
 * 
 * <p>Implement this interface, and pass it to one
 * of the {@link IndexWriter} or {@link IndexReader}
 * constructors, to customize when older
 * {@link IndexCommit point-in-time commits}
 * are deleted from the index directory.  The default deletion policy
 * is {@link KeepOnlyLastCommitDeletionPolicy}, which always
 * removes old commits as soon as a new commit is done (this
 * matches the behavior before 2.2).</p>
 *
 * <p>One expected use case for this (and the reason why it
 * was first created) is to work around problems with an
 * index directory accessed via filesystems like NFS because
 * NFS does not provide the "delete on last close" semantics
 * that Lucene's "point in time" search normally relies on.
 * By implementing a custom deletion policy, such as "a
 * commit is only removed once it has been stale for more
 * than X minutes", you can give your readers time to
 * refresh to the new commit before {@link IndexWriter}
 * removes the old commits.  Note that doing so will
 * increase the storage requirements of the index.  See <a
 * target="top"
 * href="http://issues.apache.org/jira/browse/LUCENE-710">LUCENE-710</a>
 * for details.</p>
 */

public interface IndexDeletionPolicy {

  /**
   * <p>This is called once when a writer is first
   * instantiated to give the policy a chance to remove old
   * commit points.</p>
   * 
   * <p>The writer locates all index commits present in the 
   * index directory and calls this method.  The policy may 
   * choose to delete some of the commit points, doing so by
   * calling method {@link IndexCommit#delete delete()} 
   * of {@link IndexCommit}.</p>
   * 
   * <p>Note: the last CommitPoint is the most recent one,
   * i.e. the "front index state". Be careful not to delete it,
   * unless you know for sure what you are doing, and unless 
   * you can afford to lose the index content while doing that. 
   *
   * @param commits List of current 
   * {@link IndexCommit point-in-time commits},
   *  sorted by age (the 0th one is the oldest commit).
   */
  public void onInit(List<? extends IndexCommit> commits) throws IOException;

  /**
   * <p>This is called each time the writer completed a commit.
   * This gives the policy a chance to remove old commit points
   * with each commit.</p>
   *
   * <p>The policy may now choose to delete old commit points 
   * by calling method {@link IndexCommit#delete delete()} 
   * of {@link IndexCommit}.</p>
   * 
   * <p>This method is only called when {@link
   * IndexWriter#commit} or {@link IndexWriter#close} is
   * called, or possibly not at all if the {@link
   * IndexWriter#rollback} is called.
   *
   * <p>Note: the last CommitPoint is the most recent one,
   * i.e. the "front index state". Be careful not to delete it,
   * unless you know for sure what you are doing, and unless 
   * you can afford to lose the index content while doing that.
   *  
   * @param commits List of {@link IndexCommit},
   *  sorted by age (the 0th one is the oldest commit).
   */
  public void onCommit(List<? extends IndexCommit> commits) throws IOException;
}

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