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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.language.opennlp;
import com.yahoo.language.Language;
import com.yahoo.language.detect.Detection;
import com.yahoo.language.detect.Detector;
import com.yahoo.language.detect.Hint;
import com.yahoo.language.simple.SimpleDetector;
import opennlp.tools.langdetect.LanguageDetectorConfig;
import opennlp.tools.langdetect.LanguageDetectorME;
import opennlp.tools.langdetect.LanguageDetectorModel;
import java.io.IOException;
import java.io.UncheckedIOException;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import static java.nio.charset.StandardCharsets.UTF_8;
/**
* Detects text language using patched OpenNLP, with fallback to {@link SimpleDetector} for undetected CJK input.
*
* @author jonmv
*/
class OpenNlpDetector implements Detector {
private static final Object monitor = new Object();
private static LanguageDetectorModel model;
private final SimpleDetector simple = new SimpleDetector();
private final Map<String, Language> languagesByISO3 = new HashMap<>();
private final LanguageDetectorME detector;
private final LanguageDetectorConfig config;
OpenNlpDetector() {
detector = new LanguageDetectorME(loadModel());
config = new LanguageDetectorConfig();
config.setMinDiff(0.02);
config.setChunkSize(32);
config.setMaxLength(256);
for (Locale locale : Locale.getAvailableLocales()) {
Language language = Language.fromLocale(locale);
if (language != null)
languagesByISO3.put(locale.getISO3Language(), language);
}
}
private static LanguageDetectorModel loadModel() {
synchronized (monitor) {
if (model == null) {
try {
model = new LanguageDetectorModel(OpenNlpDetector.class.getResourceAsStream("/models/langdetect-183.bin"));
}
catch (IOException e) {
throw new UncheckedIOException(e);
}
}
}
return model;
}
@Override
public Detection detect(byte[] input, int offset, int length, Hint hint) {
Charset encoding = Charset.forName(simple.guessEncoding(input, offset, length));
return new Detection(detectLanguage(new String(input, offset, length, encoding)), encoding.name(), false);
}
@Override
public Detection detect(ByteBuffer input, Hint hint) {
if (input.hasArray())
return detect(input.array(), input.arrayOffset() + input.position(), input.remaining(), hint);
byte[] buffer = new byte[input.remaining()];
input.get(buffer);
return detect(buffer, 0, buffer.length, hint);
}
@Override
public Detection detect(String input, Hint hint) {
return new Detection(detectLanguage(input), UTF_8.name(), false);
}
@SuppressWarnings("removal")
private Language detectLanguage(String input) {
var prediction = detector.probingPredictLanguages(input, config).getLanguages()[0];
var result = prediction.getConfidence() > 0.02 ? languagesByISO3.get(prediction.getLang()) : null;
return result != null ? result : simple.guessLanguage(input.substring(0, Math.min(input.length(), 256)));
}
}
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