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/*
* 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.
*/
package org.apache.mahout.vectorizer.encoders;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.mahout.common.lucene.TokenStreamIterator;
import java.io.IOException;
import java.io.Reader;
import java.nio.CharBuffer;
import java.util.Iterator;
/**
* Encodes text using a lucene style tokenizer.
*
* @see TextValueEncoder
*/
public class LuceneTextValueEncoder extends TextValueEncoder {
private Analyzer analyzer;
public LuceneTextValueEncoder(String name) {
super(name);
}
public void setAnalyzer(Analyzer analyzer) {
this.analyzer = analyzer;
}
/**
* Tokenizes a string using the simplest method. This should be over-ridden for more subtle
* tokenization.
*/
@Override
protected Iterable tokenize(CharSequence originalForm) {
try {
TokenStream ts = analyzer.tokenStream(getName(), new CharSequenceReader(originalForm));
ts.addAttribute(CharTermAttribute.class);
return new LuceneTokenIterable(ts, false);
} catch (IOException ex) {
throw new IllegalStateException(ex);
}
}
private static final class CharSequenceReader extends Reader {
private final CharBuffer buf;
/**
* Creates a new character-stream reader whose critical sections will synchronize on the reader
* itself.
*/
private CharSequenceReader(CharSequence input) {
int n = input.length();
buf = CharBuffer.allocate(n);
for (int i = 0; i < n; i++) {
buf.put(input.charAt(i));
}
buf.rewind();
}
/**
* Reads characters into a portion of an array. This method will block until some input is
* available, an I/O error occurs, or the end of the stream is reached.
*
* @param cbuf Destination buffer
* @param off Offset at which to start storing characters
* @param len Maximum number of characters to read
* @return The number of characters read, or -1 if the end of the stream has been reached
*/
@Override
public int read(char[] cbuf, int off, int len) {
int toRead = Math.min(len, buf.remaining());
if (toRead > 0) {
buf.get(cbuf, off, toRead);
return toRead;
} else {
return -1;
}
}
@Override
public void close() {
// do nothing
}
}
private static final class LuceneTokenIterable implements Iterable {
private boolean firstTime = true;
private final TokenStream tokenStream;
private LuceneTokenIterable(TokenStream ts, boolean firstTime) {
this.tokenStream = ts;
this.firstTime = firstTime;
}
/**
* Returns an iterator over a set of elements of type T.
*
* @return an Iterator.
*/
@Override
public Iterator iterator() {
if (firstTime) {
firstTime = false;
} else {
try {
tokenStream.reset();
} catch (IOException e) {
throw new IllegalStateException("This token stream can't be reset");
}
}
return new TokenStreamIterator(tokenStream);
}
}
}
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