/*
* 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.example;
import java.io.InputStream;
import java.io.Reader;
import java.util.concurrent.Executor;
import org.apache.jackrabbit.core.query.lucene.FieldNames;
import org.apache.jackrabbit.core.value.InternalValue;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.document.AbstractField;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.Field.Store;
import org.apache.lucene.document.Field.TermVector;
import org.apache.tika.metadata.Metadata;
import org.apache.tika.parser.ParseContext;
import org.apache.tika.parser.Parser;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.xml.sax.ContentHandler;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
/**
* <code>LazyTextExtractorField</code> implements a Lucene field with a String
* value that is lazily initialized from a given {@link Reader}. In addition
* this class provides a method to find out whether the purpose of the reader is
* to extract text and whether the extraction process is already finished.
*
* @see #isExtractorFinished()
*/
@SuppressWarnings("serial")
public class LazyTextExtractorField extends AbstractField {
/**
* The logger instance for this class.
*/
private static final Logger LOG = LoggerFactory.getLogger(LazyTextExtractorField.class);
/**
* The exception used to forcibly terminate the extraction process when the
* maximum field length is reached.
* <p>
* Such exceptions shouldn't be used in logging since its stack trace is meaningless.
*/
private static final SAXException STOP = new SAXException("max field length reached");
/**
* The extracted text content of the given binary value. Set to non-null
* when the text extraction task finishes.
*/
private volatile String extract = null;
/**
* Creates a new <code>LazyTextExtractorField</code> with the given
* <code>name</code>.
*
* @param name the name of the field.
* @param reader the reader where to obtain the string from.
* @param highlighting set to <code>true</code> to enable result highlighting support
*/
public LazyTextExtractorField(Parser parser, InternalValue value,
Metadata metadata, Executor executor, boolean highlighting,
int maxFieldLength) {
super(FieldNames.FULLTEXT, highlighting ? Store.YES : Store.NO,
Field.Index.ANALYZED, highlighting ? TermVector.WITH_OFFSETS
: TermVector.NO);
executor.execute(new ParsingTask(parser, value, metadata,
maxFieldLength));
}
/**
* Returns the extracted text. This method blocks until the text extraction
* task has been completed.
*
* @return the string value of this field
*/
public synchronized String stringValue() {
try {
while (!isExtractorFinished()) {
wait();
}
return extract;
} catch (InterruptedException e) {
LOG.error("Text extraction thread was interrupted", e);
return "";
}
}
/**
* @return always <code>null</code>
*/
public Reader readerValue() {
return null;
}
/**
* @return always <code>null</code>
*/
public byte[] binaryValue() {
return null;
}
/**
* @return always <code>null</code>
*/
public TokenStream tokenStreamValue() {
return null;
}
/**
* Checks whether the text extraction task has finished.
*
* @return <code>true</code> if the extracted text is available
*/
public boolean isExtractorFinished() {
return extract != null;
}
private synchronized void setExtractedText(String value) {
extract = value;
notify();
}
/**
* Releases all resources associated with this field.
*/
public void dispose() {
// TODO: Cause the ContentHandler below to throw an exception
}
/**
* The background task for extracting text from a binary value.
*/
private class ParsingTask extends DefaultHandler implements Runnable {
private final Parser parser;
private final InternalValue value;
private final Metadata metadata;
private final int maxFieldLength;
private final StringBuilder builder = new StringBuilder();
private final ParseContext context = new ParseContext();
// NOTE: not a part of Jackrabbit code, made
private final ContentHandler handler = new DefaultHandler();
public ParsingTask(Parser parser, InternalValue value,
Metadata metadata, int maxFieldLength) {
this.parser = parser;
this.value = value;
this.metadata = metadata;
this.maxFieldLength = maxFieldLength;
}
public void run() {
try {
try (InputStream stream = value.getStream()) {
parser.parse(stream, handler, metadata, context);
}
} catch (LinkageError e) {
// Capture and ignore
} catch (Throwable t) {
if (t != STOP) {
LOG.debug("Failed to extract text.", t);
setExtractedText("TextExtractionError");
return;
}
} finally {
value.discard();
}
setExtractedText(handler.toString());
}
@Override
public void characters(char[] ch, int start, int length)
throws SAXException {
builder.append(ch, start,
Math.min(length, maxFieldLength - builder.length()));
if (builder.length() >= maxFieldLength) {
throw STOP;
}
}
@Override
public void ignorableWhitespace(char[] ch, int start, int length)
throws SAXException {
characters(ch, start, length);
}
}
}