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Lucene example source code file (WildcardTermEnum.java)

This example Lucene source code file (WildcardTermEnum.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

filteredtermenum, io, ioexception, override, override, string, string, term, wildcard_char, wildcard_char, wildcard_string, wildcard_string, wildcardtermenum

The Lucene WildcardTermEnum.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;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;

/**
 * Subclass of FilteredTermEnum for enumerating all terms that match the
 * specified wildcard filter term.
 * <p>
 * Term enumerations are always ordered by Term.compareTo().  Each term in
 * the enumeration is greater than all that precede it.
 */
public class WildcardTermEnum extends FilteredTermEnum {
  final Term searchTerm;
  final String field;
  final String text;
  final String pre;
  final int preLen;
  boolean endEnum = false;

  /**
   * Creates a new <code>WildcardTermEnum.
   * <p>
   * After calling the constructor the enumeration is already pointing to the first 
   * valid term if such a term exists.
   */
  public WildcardTermEnum(IndexReader reader, Term term) throws IOException {
    super();
    searchTerm = term;
    field = searchTerm.field();
    final String searchTermText = searchTerm.text();

    final int sidx = searchTermText.indexOf(WILDCARD_STRING);
    final int cidx = searchTermText.indexOf(WILDCARD_CHAR);
    int idx = sidx;
    if (idx == -1) {
      idx = cidx;
    }
    else if (cidx >= 0) {
      idx = Math.min(idx, cidx);
    }
    pre = idx != -1?searchTerm.text().substring(0,idx): "";

    preLen = pre.length();
    text = searchTermText.substring(preLen);
    setEnum(reader.terms(new Term(searchTerm.field(), pre)));
  }

  @Override
  protected final boolean termCompare(Term term) {
    if (field == term.field()) {
      String searchText = term.text();
      if (searchText.startsWith(pre)) {
        return wildcardEquals(text, 0, searchText, preLen);
      }
    }
    endEnum = true;
    return false;
  }

  @Override
  public float difference() {
    return 1.0f;
  }

  @Override
  public final boolean endEnum() {
    return endEnum;
  }

  /********************************************
   * String equality with support for wildcards
   ********************************************/

  public static final char WILDCARD_STRING = '*';
  public static final char WILDCARD_CHAR = '?';

  /**
   * Determines if a word matches a wildcard pattern.
   * <small>Work released by Granta Design Ltd after originally being done on
   * company time.</small>
   */
  public static final boolean wildcardEquals(String pattern, int patternIdx,
    String string, int stringIdx)
  {
    int p = patternIdx;
    
    for (int s = stringIdx; ; ++p, ++s)
      {
        // End of string yet?
        boolean sEnd = (s >= string.length());
        // End of pattern yet?
        boolean pEnd = (p >= pattern.length());

        // If we're looking at the end of the string...
        if (sEnd)
        {
          // Assume the only thing left on the pattern is/are wildcards
          boolean justWildcardsLeft = true;

          // Current wildcard position
          int wildcardSearchPos = p;
          // While we haven't found the end of the pattern,
          // and haven't encountered any non-wildcard characters
          while (wildcardSearchPos < pattern.length() && justWildcardsLeft)
          {
            // Check the character at the current position
            char wildchar = pattern.charAt(wildcardSearchPos);
            
            // If it's not a wildcard character, then there is more
            // pattern information after this/these wildcards.
            if (wildchar != WILDCARD_CHAR && wildchar != WILDCARD_STRING)
            {
              justWildcardsLeft = false;
            }
            else
            {
              // to prevent "cat" matches "ca??"
              if (wildchar == WILDCARD_CHAR) {
                return false;
              }
              
              // Look at the next character
              wildcardSearchPos++;
            }
          }

          // This was a prefix wildcard search, and we've matched, so
          // return true.
          if (justWildcardsLeft)
          {
            return true;
          }
        }

        // If we've gone past the end of the string, or the pattern,
        // return false.
        if (sEnd || pEnd)
        {
          break;
        }

        // Match a single character, so continue.
        if (pattern.charAt(p) == WILDCARD_CHAR)
        {
          continue;
        }

        //
        if (pattern.charAt(p) == WILDCARD_STRING)
        {
          // Look at the character beyond the '*' characters.
          while (p < pattern.length() && pattern.charAt(p) == WILDCARD_STRING)
            ++p;
          // Examine the string, starting at the last character.
          for (int i = string.length(); i >= s; --i)
          {
            if (wildcardEquals(pattern, p, string, i))
            {
              return true;
            }
          }
          break;
        }
        if (pattern.charAt(p) != string.charAt(s))
        {
          break;
        }
      }
      return false;
  }
}

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