package org.apache.lucene.analysis.th;
/**
* Copyright 2006 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 java.io.IOException;
import java.lang.Character.UnicodeBlock;
import java.text.BreakIterator;
import java.util.Locale;
import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.core.LowerCaseFilter;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
import org.apache.lucene.analysis.util.CharArrayIterator;
import org.apache.lucene.util.AttributeSource;
import org.apache.lucene.util.Version;
/**
* {@link TokenFilter} that use {@link java.text.BreakIterator} to break each
* Token that is Thai into separate Token(s) for each Thai word.
* <p>Please note: Since matchVersion 3.1 on, this filter no longer lowercases non-thai text.
* {@link ThaiAnalyzer} will insert a {@link LowerCaseFilter} before this filter
* so the behaviour of the Analyzer does not change. With version 3.1, the filter handles
* position increments correctly.
* <p>WARNING: this filter may not be supported by all JREs.
* It is known to work with Sun/Oracle and Harmony JREs.
* If your application needs to be fully portable, consider using ICUTokenizer instead,
* which uses an ICU Thai BreakIterator that will always be available.
*/
public final class ThaiWordFilter extends TokenFilter {
/**
* True if the JRE supports a working dictionary-based breakiterator for Thai.
* If this is false, this filter will not work at all!
*/
public static final boolean DBBI_AVAILABLE;
private static final BreakIterator proto = BreakIterator.getWordInstance(new Locale("th"));
static {
// check that we have a working dictionary-based break iterator for thai
proto.setText("ภาษาไทย");
DBBI_AVAILABLE = proto.isBoundary(4);
}
private final BreakIterator breaker = (BreakIterator) proto.clone();
private final CharArrayIterator charIterator = CharArrayIterator.newWordInstance();
private final boolean handlePosIncr;
private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);
private final OffsetAttribute offsetAtt = addAttribute(OffsetAttribute.class);
private final PositionIncrementAttribute posAtt = addAttribute(PositionIncrementAttribute.class);
private AttributeSource clonedToken = null;
private CharTermAttribute clonedTermAtt = null;
private OffsetAttribute clonedOffsetAtt = null;
private boolean hasMoreTokensInClone = false;
private boolean hasIllegalOffsets = false; // only if the length changed before this filter
/** Creates a new ThaiWordFilter with the specified match version. */
public ThaiWordFilter(Version matchVersion, TokenStream input) {
super(matchVersion.onOrAfter(Version.LUCENE_31) ?
input : new LowerCaseFilter(matchVersion, input));
if (!DBBI_AVAILABLE)
throw new UnsupportedOperationException("This JRE does not have support for Thai segmentation");
handlePosIncr = matchVersion.onOrAfter(Version.LUCENE_31);
}
@Override
public boolean incrementToken() throws IOException {
if (hasMoreTokensInClone) {
int start = breaker.current();
int end = breaker.next();
if (end != BreakIterator.DONE) {
clonedToken.copyTo(this);
termAtt.copyBuffer(clonedTermAtt.buffer(), start, end - start);
if (hasIllegalOffsets) {
offsetAtt.setOffset(clonedOffsetAtt.startOffset(), clonedOffsetAtt.endOffset());
} else {
offsetAtt.setOffset(clonedOffsetAtt.startOffset() + start, clonedOffsetAtt.startOffset() + end);
}
if (handlePosIncr) posAtt.setPositionIncrement(1);
return true;
}
hasMoreTokensInClone = false;
}
if (!input.incrementToken()) {
return false;
}
if (termAtt.length() == 0 || UnicodeBlock.of(termAtt.charAt(0)) != UnicodeBlock.THAI) {
return true;
}
hasMoreTokensInClone = true;
// if length by start + end offsets doesn't match the term text then assume
// this is a synonym and don't adjust the offsets.
hasIllegalOffsets = offsetAtt.endOffset() - offsetAtt.startOffset() != termAtt.length();
// we lazy init the cloned token, as in ctor not all attributes may be added
if (clonedToken == null) {
clonedToken = cloneAttributes();
clonedTermAtt = clonedToken.getAttribute(CharTermAttribute.class);
clonedOffsetAtt = clonedToken.getAttribute(OffsetAttribute.class);
} else {
this.copyTo(clonedToken);
}
// reinit CharacterIterator
charIterator.setText(clonedTermAtt.buffer(), 0, clonedTermAtt.length());
breaker.setText(charIterator);
int end = breaker.next();
if (end != BreakIterator.DONE) {
termAtt.setLength(end);
if (hasIllegalOffsets) {
offsetAtt.setOffset(clonedOffsetAtt.startOffset(), clonedOffsetAtt.endOffset());
} else {
offsetAtt.setOffset(clonedOffsetAtt.startOffset(), clonedOffsetAtt.startOffset() + end);
}
// position increment keeps as it is for first token
return true;
}
return false;
}
@Override
public void reset() throws IOException {
super.reset();
hasMoreTokensInClone = false;
clonedToken = null;
clonedTermAtt = null;
clonedOffsetAtt = null;
}
}