package org.apache.lucene.collation;
/**
* 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 org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.util.IndexableBinaryStringTools;
import java.io.IOException;
import java.text.Collator;
/**
* <p>
* Converts each token into its {@link java.text.CollationKey}, and then
* encodes the CollationKey with {@link IndexableBinaryStringTools}, to allow
* it to be stored as an index term.
* </p>
* <p>
* <strong>WARNING:</strong> Make sure you use exactly the same Collator at
* index and query time -- CollationKeys are only comparable when produced by
* the same Collator. Since {@link java.text.RuleBasedCollator}s are not
* independently versioned, it is unsafe to search against stored
* CollationKeys unless the following are exactly the same (best practice is
* to store this information with the index and check that they remain the
* same at query time):
* </p>
* <ol>
* <li>JVM vendor</li>
* <li>JVM version, including patch version</li>
* <li>
* The language (and country and variant, if specified) of the Locale
* used when constructing the collator via
* {@link Collator#getInstance(java.util.Locale)}.
* </li>
* <li>
* The collation strength used - see {@link Collator#setStrength(int)}
* </li>
* </ol>
* <p>
* The <code>ICUCollationKeyFilter</code> in the icu package of Lucene's
* contrib area uses ICU4J's Collator, which makes its
* version available, thus allowing collation to be versioned independently
* from the JVM. ICUCollationKeyFilter is also significantly faster and
* generates significantly shorter keys than CollationKeyFilter. See
* <a href="http://site.icu-project.org/charts/collation-icu4j-sun"
* >http://site.icu-project.org/charts/collation-icu4j-sun</a> for key
* generation timing and key length comparisons between ICU4J and
* java.text.Collator over several languages.
* </p>
* <p>
* CollationKeys generated by java.text.Collators are not compatible
* with those those generated by ICU Collators. Specifically, if you use
* CollationKeyFilter to generate index terms, do not use
* ICUCollationKeyFilter on the query side, or vice versa.
* </p>
*/
public final class CollationKeyFilter extends TokenFilter {
private final Collator collator;
private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
/**
* @param input Source token stream
* @param collator CollationKey generator
*/
public CollationKeyFilter(TokenStream input, Collator collator) {
super(input);
this.collator = collator;
}
@Override
public boolean incrementToken() throws IOException {
if (input.incrementToken()) {
byte[] collationKey = collator.getCollationKey(termAtt.toString()).toByteArray();
int encodedLength = IndexableBinaryStringTools.getEncodedLength(
collationKey, 0, collationKey.length);
termAtt.resizeBuffer(encodedLength);
termAtt.setLength(encodedLength);
IndexableBinaryStringTools.encode(collationKey, 0, collationKey.length,
termAtt.buffer(), 0, encodedLength);
return true;
} else {
return false;
}
}
}