alvinalexander.com | career | drupal | java | mac | mysql | perl | scala | uml | unix  

What this is

This file 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.

Other links

The source code

package org.apache.lucene.search;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed 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 org.apache.lucene.index.IndexReader;
import java.util.BitSet;
import java.util.WeakHashMap;
import java.util.Map;
import java.io.IOException;

/**
 * Wraps another filters result and caches it.  The caching
 * behavior is like {@link QueryFilter}.  The purpose is to allow
 * filters to simply filter, and then wrap with this class to add
 * caching, keeping the two concerns decoupled yet composable.
 */
public class CachingWrapperFilter extends Filter {
  private Filter filter;

  /**
   * @todo What about serialization in RemoteSearchable?  Caching won't work.
   *       Should transient be removed?
   */
  private transient Map cache;

  /**
   * @param filter Filter to cache results of
   */
  public CachingWrapperFilter(Filter filter) {
    this.filter = filter;
  }

  public BitSet bits(IndexReader reader) throws IOException {
    if (cache == null) {
      cache = new WeakHashMap();
    }

    synchronized (cache) {  // check cache
      BitSet cached = (BitSet) cache.get(reader);
      if (cached != null) {
        return cached;
      }
    }

    final BitSet bits = filter.bits(reader);

    synchronized (cache) {  // update cache
      cache.put(reader, bits);
    }

    return bits;
  }

  public String toString() {
    return "CachingWrapperFilter("+filter+")";
  }
}
... this post is sponsored by my books ...

#1 New Release!

FP Best Seller

 

new blog posts

 

Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.