prefixquery.java

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package org.apache.lucene.search;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache Lucene" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
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 *
 * 5. Products derived from this software may not be called "Apache",
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 *
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

import java.io.IOException;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermEnum;
import org.apache.lucene.index.TermDocs;
import org.apache.lucene.index.IndexReader;

/** A Query that matches documents containing terms with a specified prefix. */
final public class PrefixQuery extends Query {
  private Term prefix;
  private IndexReader reader;
  private BooleanQuery query;

  /** Constructs a query for terms starting with <code>prefix</code>. */
  public PrefixQuery(Term prefix) {
    this.prefix = prefix;
    this.reader = reader;
  }

  final void prepare(IndexReader reader) {
    this.query = null;
    this.reader = reader;
  }

  final float sumOfSquaredWeights(Searcher searcher)
    throws IOException {
    return getQuery().sumOfSquaredWeights(searcher);
  }

  void normalize(float norm) {
    try {
      getQuery().normalize(norm);
    } catch (IOException e) {
      throw new RuntimeException(e.toString());
    }
  }

  Scorer scorer(IndexReader reader) throws IOException {
    return getQuery().scorer(reader);
  }

  private BooleanQuery getQuery() throws IOException {
    if (query == null) {
      BooleanQuery q = new BooleanQuery();
      TermEnum enum = reader.terms(prefix);
      try {
	String prefixText = prefix.text();
	String prefixField = prefix.field();
	do {
	  Term term = enum.term();
	  if (term != null &&
	      term.text().startsWith(prefixText) &&
	      term.field() == prefixField) {
	    TermQuery tq = new TermQuery(term);	  // found a match
	    tq.setBoost(boost);			  // set the boost
	    q.add(tq, false, false);		  // add to q
	    //System.out.println("added " + term);
	  } else {
	    break;
	  }
	} while (enum.next());
      } finally {
	enum.close();
      }
      query = q;
    }
    return query;
  }

  /** Prints a user-readable version of this query. */
  public String toString(String field) {
    StringBuffer buffer = new StringBuffer();
    if (!prefix.field().equals(field)) {
      buffer.append(prefix.field());
      buffer.append(":");
    }
    buffer.append(prefix.text());
    buffer.append('*');
    if (boost != 1.0f) {
      buffer.append("^");
      buffer.append(Float.toString(boost));
    }
    return buffer.toString();
  }
}