CompositeEncodingDetector.java
/*
* 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.tika.detect;
import java.io.IOException;
import java.io.Serializable;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.tika.io.TikaInputStream;
import org.apache.tika.metadata.Metadata;
import org.apache.tika.metadata.TikaCoreProperties;
import org.apache.tika.parser.ParseContext;
/**
* A composite encoding detector that runs child detectors.
*
* <p>If a {@link MetaEncodingDetector} is among the children, this
* composite switches from first-match-wins to collect-all mode:
* all base detectors run first and their results are collected in an
* {@link EncodingDetectorContext}, then the meta detector runs last
* to arbitrate. Only one meta detector is supported.</p>
*
* <p>If no meta detector is present, the first non-empty result wins
* (traditional behavior).</p>
*/
public class CompositeEncodingDetector implements EncodingDetector, Serializable {
private static final long serialVersionUID = 5980683158436430252L;
private static final Logger LOG =
LoggerFactory.getLogger(CompositeEncodingDetector.class);
private final List<EncodingDetector> detectors;
private final List<EncodingDetector> baseDetectors;
private final MetaEncodingDetector metaDetector;
public CompositeEncodingDetector(List<EncodingDetector> detectors,
Collection<Class<? extends EncodingDetector>>
excludeEncodingDetectors) {
this.detectors = new ArrayList<>();
for (EncodingDetector encodingDetector : detectors) {
if (!isExcluded(excludeEncodingDetectors, encodingDetector.getClass())) {
this.detectors.add(encodingDetector);
}
}
this.baseDetectors = new ArrayList<>();
this.metaDetector = partition(this.detectors, baseDetectors);
}
public CompositeEncodingDetector(List<EncodingDetector> detectors) {
this.detectors = new ArrayList<>(detectors);
this.baseDetectors = new ArrayList<>();
this.metaDetector = partition(this.detectors, baseDetectors);
}
private static MetaEncodingDetector partition(
List<EncodingDetector> all, List<EncodingDetector> base) {
MetaEncodingDetector meta = null;
for (EncodingDetector d : all) {
if (d instanceof MetaEncodingDetector) {
if (meta == null) {
meta = (MetaEncodingDetector) d;
} else {
LOG.warn("Multiple MetaEncodingDetectors found; ignoring {}",
d.getClass().getName());
}
} else {
base.add(d);
}
}
return meta;
}
@Override
public List<EncodingResult> detect(TikaInputStream tis, Metadata metadata,
ParseContext parseContext) throws IOException {
if (metaDetector != null) {
return detectWithMeta(tis, metadata, parseContext);
}
return detectFirstMatch(tis, metadata, parseContext);
}
/**
* Traditional first-match-wins behavior: returns the results from the
* first detector that produces a non-empty list.
*/
private List<EncodingResult> detectFirstMatch(TikaInputStream tis, Metadata metadata,
ParseContext parseContext)
throws IOException {
for (EncodingDetector detector : getDetectors()) {
List<EncodingResult> results = detector.detect(tis, metadata, parseContext);
if (!results.isEmpty()) {
Charset detected = results.get(0).getCharset();
metadata.set(TikaCoreProperties.DETECTED_ENCODING, detected.name());
if (!detector.getClass().getSimpleName()
.equals("CompositeEncodingDetector")) {
metadata.set(TikaCoreProperties.ENCODING_DETECTOR,
detector.getClass().getSimpleName());
}
return results;
}
}
return Collections.emptyList();
}
/**
* Collect-all mode: run every base detector, populate context,
* then let the meta detector arbitrate.
*
* <p>The stream is marked once before the base-detector loop. After all
* base detectors have run (potentially consuming the stream), it is reset
* to that mark so the meta detector can re-read the raw bytes for
* language-based arbitration. Base detectors are not reset between
* themselves ��� each handles its own mark/reset internally if needed.</p>
*/
private List<EncodingResult> detectWithMeta(TikaInputStream tis, Metadata metadata,
ParseContext parseContext)
throws IOException {
EncodingDetectorContext context = new EncodingDetectorContext();
parseContext.set(EncodingDetectorContext.class, context);
try {
for (EncodingDetector detector : baseDetectors) {
List<EncodingResult> detected = detector.detect(tis, metadata, parseContext);
if (!detected.isEmpty()) {
context.addResult(detected, detector.getClass().getSimpleName());
}
}
// Each base detector handles its own mark/reset, so the stream is
// back at the start here. CharSoup handles its own mark/reset too.
List<EncodingResult> metaResults =
metaDetector.detect(tis, metadata, parseContext);
List<EncodingResult> finalResults;
String detectorName;
if (metaResults.isEmpty() && !context.getResults().isEmpty()) {
// Meta detector abstained ��� fall back to first base detector's results
EncodingDetectorContext.Result first = context.getResults().get(0);
finalResults = first.getEncodingResults();
detectorName = first.getDetectorName();
} else if (!metaResults.isEmpty()) {
finalResults = metaResults;
Charset winner = metaResults.get(0).getCharset();
// Credit the base detector that originally proposed the winning charset
detectorName = metaDetector.getClass().getSimpleName();
for (EncodingDetectorContext.Result r : context.getResults()) {
if (r.getCharset().equals(winner)) {
detectorName = r.getDetectorName();
break;
}
}
} else {
return Collections.emptyList();
}
Charset detected = finalResults.get(0).getCharset();
metadata.set(TikaCoreProperties.DETECTED_ENCODING, detected.name());
metadata.set(TikaCoreProperties.ENCODING_DETECTOR, detectorName);
metadata.set(TikaCoreProperties.ENCODING_DETECTION_TRACE, buildTrace(context));
return finalResults;
} finally {
parseContext.set(EncodingDetectorContext.class, null);
}
}
private static String buildTrace(EncodingDetectorContext context) {
StringBuilder sb = new StringBuilder();
for (EncodingDetectorContext.Result r : context.getResults()) {
if (sb.length() > 0) {
sb.append(", ");
}
sb.append(r.getDetectorName()).append("->").append(r.getCharset().name());
sb.append("[").append(r.getResultType()).append("]");
if (r.getResultType() == EncodingResult.ResultType.STATISTICAL) {
sb.append(String.format(java.util.Locale.ROOT, "(%.2f)", r.getConfidence()));
}
}
String info = context.getArbitrationInfo();
if (info != null) {
sb.append(" [").append(info).append("]");
}
return sb.toString();
}
public List<EncodingDetector> getDetectors() {
return Collections.unmodifiableList(detectors);
}
private boolean isExcluded(
Collection<Class<? extends EncodingDetector>> excludeEncodingDetectors,
Class<? extends EncodingDetector> encodingDetector) {
return excludeEncodingDetectors.contains(encodingDetector) ||
assignableFrom(excludeEncodingDetectors, encodingDetector);
}
private boolean assignableFrom(
Collection<Class<? extends EncodingDetector>> excludeEncodingDetectors,
Class<? extends EncodingDetector> encodingDetector) {
for (Class<? extends EncodingDetector> e : excludeEncodingDetectors) {
if (e.isAssignableFrom(encodingDetector)) {
return true;
}
}
return false;
}
}