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Lucene example source code file (FilteredDocIdSet.java)

This example Lucene source code file (FilteredDocIdSet.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

docidset, docidset, docidsetiterator, filtereddocidset, filtereddocidset, io, ioexception, ioexception, override, override

The Lucene FilteredDocIdSet.java source code

package org.apache.lucene.search;

/**
 * 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.io.IOException;

/**
 * Abstract decorator class for a DocIdSet implementation
 * that provides on-demand filtering/validation
 * mechanism on a given DocIdSet.
 *
 * <p/>
 *
 * Technically, this same functionality could be achieved
 * with ChainedFilter (under contrib/misc), however the
 * benefit of this class is it never materializes the full
 * bitset for the filter.  Instead, the {@link #match}
 * method is invoked on-demand, per docID visited during
 * searching.  If you know few docIDs will be visited, and
 * the logic behind {@link #match} is relatively costly,
 * this may be a better way to filter than ChainedFilter.
 *
 * @see DocIdSet
 */

public abstract class FilteredDocIdSet extends DocIdSet {
  private final DocIdSet _innerSet;
  
  /**
   * Constructor.
   * @param innerSet Underlying DocIdSet
   */
  public FilteredDocIdSet(DocIdSet innerSet) {
    _innerSet = innerSet;
  }
  
  /** This DocIdSet implementation is cacheable if the inner set is cacheable. */
  @Override
  public boolean isCacheable() {
    return _innerSet.isCacheable();
  }

  /**
   * Validation method to determine whether a docid should be in the result set.
   * @param docid docid to be tested
   * @return true if input docid should be in the result set, false otherwise.
   */
  protected abstract boolean match(int docid) throws IOException;
	
  /**
   * Implementation of the contract to build a DocIdSetIterator.
   * @see DocIdSetIterator
   * @see FilteredDocIdSetIterator
   */
  @Override
  public DocIdSetIterator iterator() throws IOException {
    return new FilteredDocIdSetIterator(_innerSet.iterator()) {
      @Override
      protected boolean match(int docid) throws IOException {
        return FilteredDocIdSet.this.match(docid);
      }
    };
  }
}

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