org.apache.lucene.search.highlight.Highlighter Maven / Gradle / Ivy
Show all versions of lucene-highlighter Show documentation
/*
* 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.lucene.search.highlight;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Objects;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.util.PriorityQueue;
/**
* Marks up highlighted terms found in the best sections of text, using configurable {@link
* Fragmenter}, {@link Scorer}, {@link Formatter}, {@link Encoder} and tokenizers.
*
* This is Lucene's original Highlighter; there are others.
*/
public class Highlighter {
public static final int DEFAULT_MAX_CHARS_TO_ANALYZE = 50 * 1024;
private Formatter formatter;
private Encoder encoder;
private Scorer fragmentScorer;
private int maxDocCharsToAnalyze = DEFAULT_MAX_CHARS_TO_ANALYZE;
private Fragmenter textFragmenter = new SimpleFragmenter();
public Highlighter(Scorer fragmentScorer) {
this(new SimpleHTMLFormatter(), fragmentScorer);
}
public Highlighter(Formatter formatter, Scorer fragmentScorer) {
this(formatter, new DefaultEncoder(), fragmentScorer);
}
public Highlighter(Formatter formatter, Encoder encoder, Scorer fragmentScorer) {
ensureArgumentNotNull(formatter, "'formatter' must not be null");
ensureArgumentNotNull(encoder, "'encoder' must not be null");
ensureArgumentNotNull(fragmentScorer, "'fragmentScorer' must not be null");
this.formatter = formatter;
this.encoder = encoder;
this.fragmentScorer = fragmentScorer;
}
/**
* Highlights chosen terms in a text, extracting the most relevant section. This is a convenience
* method that calls {@link #getBestFragment(TokenStream, String)}
*
* @param analyzer the analyzer that will be used to split text into chunks
* @param text text to highlight terms in
* @param fieldName Name of field used to influence analyzer's tokenization policy
* @return highlighted text fragment or null if no terms found
* @throws InvalidTokenOffsetsException thrown if any token's endOffset exceeds the provided
* text's length
*/
public final String getBestFragment(Analyzer analyzer, String fieldName, String text)
throws IOException, InvalidTokenOffsetsException {
TokenStream tokenStream = analyzer.tokenStream(fieldName, text);
return getBestFragment(tokenStream, text);
}
/**
* Highlights chosen terms in a text, extracting the most relevant section. The document text is
* analysed in chunks to record hit statistics across the document. After accumulating stats, the
* fragment with the highest score is returned
*
* @param tokenStream a stream of tokens identified in the text parameter, including offset
* information. This is typically produced by an analyzer re-parsing a document's text. Some
* work may be done on retrieving TokenStreams more efficiently by adding support for storing
* original text position data in the Lucene index but this support is not currently available
* (as of Lucene 1.4 rc2).
* @param text text to highlight terms in
* @return highlighted text fragment or null if no terms found
* @throws InvalidTokenOffsetsException thrown if any token's endOffset exceeds the provided
* text's length
*/
public final String getBestFragment(TokenStream tokenStream, String text)
throws IOException, InvalidTokenOffsetsException {
String[] results = getBestFragments(tokenStream, text, 1);
if (results.length > 0) {
return results[0];
}
return null;
}
/**
* Highlights chosen terms in a text, extracting the most relevant sections. This is a convenience
* method that calls {@link #getBestFragments(TokenStream, String, int)}
*
* @param analyzer the analyzer that will be used to split text into chunks
* @param fieldName the name of the field being highlighted (used by analyzer)
* @param text text to highlight terms in
* @param maxNumFragments the maximum number of fragments.
* @return highlighted text fragments (between 0 and maxNumFragments number of fragments)
* @throws InvalidTokenOffsetsException thrown if any token's endOffset exceeds the provided
* text's length
*/
public final String[] getBestFragments(
Analyzer analyzer, String fieldName, String text, int maxNumFragments)
throws IOException, InvalidTokenOffsetsException {
TokenStream tokenStream = analyzer.tokenStream(fieldName, text);
return getBestFragments(tokenStream, text, maxNumFragments);
}
/**
* Highlights chosen terms in a text, extracting the most relevant sections. The document text is
* analysed in chunks to record hit statistics across the document. After accumulating stats, the
* fragments with the highest scores are returned as an array of strings in order of score
* (contiguous fragments are merged into one in their original order to improve readability)
*
* @param text text to highlight terms in
* @param maxNumFragments the maximum number of fragments.
* @return highlighted text fragments (between 0 and maxNumFragments number of fragments)
* @throws InvalidTokenOffsetsException thrown if any token's endOffset exceeds the provided
* text's length
*/
public final String[] getBestFragments(TokenStream tokenStream, String text, int maxNumFragments)
throws IOException, InvalidTokenOffsetsException {
maxNumFragments = Math.max(1, maxNumFragments); // sanity check
TextFragment[] frag = getBestTextFragments(tokenStream, text, true, maxNumFragments);
// Get text
ArrayList fragTexts = new ArrayList<>();
for (int i = 0; i < frag.length; i++) {
if ((frag[i] != null) && (frag[i].getScore() > 0)) {
fragTexts.add(frag[i].toString());
}
}
return fragTexts.toArray(new String[0]);
}
/**
* Low level api to get the most relevant (formatted) sections of the document. This method has
* been made public to allow visibility of score information held in TextFragment objects. Thanks
* to Jason Calabrese for help in redefining the interface.
*
* @throws IOException If there is a low-level I/O error
* @throws InvalidTokenOffsetsException thrown if any token's endOffset exceeds the provided
* text's length
*/
public final TextFragment[] getBestTextFragments(
TokenStream tokenStream, String text, boolean mergeContiguousFragments, int maxNumFragments)
throws IOException, InvalidTokenOffsetsException {
ArrayList docFrags = new ArrayList<>();
StringBuilder newText = new StringBuilder();
CharTermAttribute termAtt = tokenStream.addAttribute(CharTermAttribute.class);
OffsetAttribute offsetAtt = tokenStream.addAttribute(OffsetAttribute.class);
TextFragment currentFrag = new TextFragment(newText, newText.length(), docFrags.size());
if (fragmentScorer instanceof QueryScorer) {
((QueryScorer) fragmentScorer).setMaxDocCharsToAnalyze(maxDocCharsToAnalyze);
}
TokenStream newStream = fragmentScorer.init(tokenStream);
if (newStream != null) {
tokenStream = newStream;
}
fragmentScorer.startFragment(currentFrag);
docFrags.add(currentFrag);
FragmentQueue fragQueue = new FragmentQueue(maxNumFragments);
try {
String tokenText;
int startOffset;
int endOffset;
int lastEndOffset = 0;
textFragmenter.start(text, tokenStream);
TokenGroup tokenGroup = new TokenGroup(tokenStream);
tokenStream.reset();
for (boolean next = tokenStream.incrementToken();
next && (offsetAtt.startOffset() < maxDocCharsToAnalyze);
next = tokenStream.incrementToken()) {
if ((offsetAtt.endOffset() > text.length()) || (offsetAtt.startOffset() > text.length())) {
throw new InvalidTokenOffsetsException(
"Token "
+ termAtt.toString()
+ " exceeds length of provided text sized "
+ text.length());
}
if ((tokenGroup.getNumTokens() > 0) && (tokenGroup.isDistinct())) {
// the current token is distinct from previous tokens -
// markup the cached token group info
startOffset = tokenGroup.getStartOffset();
endOffset = tokenGroup.getEndOffset();
tokenText = text.substring(startOffset, endOffset);
String markedUpText = formatter.highlightTerm(encoder.encodeText(tokenText), tokenGroup);
// store any whitespace etc from between this and last group
if (startOffset > lastEndOffset)
newText.append(encoder.encodeText(text.substring(lastEndOffset, startOffset)));
newText.append(markedUpText);
lastEndOffset = Math.max(endOffset, lastEndOffset);
tokenGroup.clear();
// check if current token marks the start of a new fragment
if (textFragmenter.isNewFragment()) {
currentFrag.setScore(fragmentScorer.getFragmentScore());
// record stats for a new fragment
currentFrag.textEndPos = newText.length();
currentFrag = new TextFragment(newText, newText.length(), docFrags.size());
fragmentScorer.startFragment(currentFrag);
docFrags.add(currentFrag);
}
}
tokenGroup.addToken(fragmentScorer.getTokenScore());
// if(lastEndOffset>maxDocBytesToAnalyze)
// {
// break;
// }
}
currentFrag.setScore(fragmentScorer.getFragmentScore());
if (tokenGroup.getNumTokens() > 0) {
// flush the accumulated text (same code as in above loop)
startOffset = tokenGroup.getStartOffset();
endOffset = tokenGroup.getEndOffset();
tokenText = text.substring(startOffset, endOffset);
String markedUpText = formatter.highlightTerm(encoder.encodeText(tokenText), tokenGroup);
// store any whitespace etc from between this and last group
if (startOffset > lastEndOffset)
newText.append(encoder.encodeText(text.substring(lastEndOffset, startOffset)));
newText.append(markedUpText);
lastEndOffset = Math.max(lastEndOffset, endOffset);
}
// Test what remains of the original text beyond the point where we stopped analyzing
if (
// if there is text beyond the last token considered..
(lastEndOffset < text.length())
&&
// and that text is not too large...
(text.length() <= maxDocCharsToAnalyze)) {
// append it to the last fragment
newText.append(encoder.encodeText(text.substring(lastEndOffset)));
}
currentFrag.textEndPos = newText.length();
// sort the most relevant sections of the text
for (Iterator i = docFrags.iterator(); i.hasNext(); ) {
currentFrag = i.next();
// If you are running with a version of Lucene before 11th Sept 03
// you do not have PriorityQueue.insert() - so uncomment the code below
/*
if (currentFrag.getScore() >= minScore)
{
fragQueue.put(currentFrag);
if (fragQueue.size() > maxNumFragments)
{ // if hit queue overfull
fragQueue.pop(); // remove lowest in hit queue
minScore = ((TextFragment) fragQueue.top()).getScore(); // reset minScore
}
}
*/
// The above code caused a problem as a result of Christoph Goller's 11th Sept 03
// fix to PriorityQueue. The correct method to use here is the new "insert" method
// USE ABOVE CODE IF THIS DOES NOT COMPILE!
fragQueue.insertWithOverflow(currentFrag);
}
// return the most relevant fragments
TextFragment[] frag = new TextFragment[fragQueue.size()];
for (int i = frag.length - 1; i >= 0; i--) {
frag[i] = fragQueue.pop();
}
// merge any contiguous fragments to improve readability
if (mergeContiguousFragments) {
mergeContiguousFragments(frag);
ArrayList fragTexts = new ArrayList<>();
for (int i = 0; i < frag.length; i++) {
if ((frag[i] != null) && (frag[i].getScore() > 0)) {
fragTexts.add(frag[i]);
}
}
frag = fragTexts.toArray(new TextFragment[0]);
}
return frag;
} finally {
if (tokenStream != null) {
try {
tokenStream.end();
tokenStream.close();
} catch (
@SuppressWarnings("unused")
Exception e) {
}
}
}
}
/**
* Improves readability of a score-sorted list of TextFragments by merging any fragments that were
* contiguous in the original text into one larger fragment with the correct order. This will
* leave a "null" in the array entry for the lesser scored fragment.
*
* @param frag An array of document fragments in descending score
*/
private void mergeContiguousFragments(TextFragment[] frag) {
boolean mergingStillBeingDone;
if (frag.length > 1)
do {
mergingStillBeingDone = false; // initialise loop control flag
// for each fragment, scan other frags looking for contiguous blocks
for (int i = 0; i < frag.length; i++) {
if (frag[i] == null) {
continue;
}
// merge any contiguous blocks
for (int x = 0; x < frag.length; x++) {
if (frag[x] == null) {
continue;
}
if (frag[i] == null) {
break;
}
TextFragment frag1 = null;
TextFragment frag2 = null;
int frag1Num = 0;
int frag2Num = 0;
int bestScoringFragNum;
int worstScoringFragNum;
// if blocks are contiguous....
if (frag[i].follows(frag[x])) {
frag1 = frag[x];
frag1Num = x;
frag2 = frag[i];
frag2Num = i;
} else if (frag[x].follows(frag[i])) {
frag1 = frag[i];
frag1Num = i;
frag2 = frag[x];
frag2Num = x;
}
// merging required..
if (frag1 != null) {
if (frag1.getScore() > frag2.getScore()) {
bestScoringFragNum = frag1Num;
worstScoringFragNum = frag2Num;
} else {
bestScoringFragNum = frag2Num;
worstScoringFragNum = frag1Num;
}
frag1.merge(frag2);
frag[worstScoringFragNum] = null;
mergingStillBeingDone = true;
frag[bestScoringFragNum] = frag1;
}
}
}
} while (mergingStillBeingDone);
}
/**
* Highlights terms in the text , extracting the most relevant sections and concatenating the
* chosen fragments with a separator (typically "..."). The document text is analysed in chunks to
* record hit statistics across the document. After accumulating stats, the fragments with the
* highest scores are returned in order as "separator" delimited strings.
*
* @param text text to highlight terms in
* @param maxNumFragments the maximum number of fragments.
* @param separator the separator used to intersperse the document fragments (typically "...")
* @return highlighted text
* @throws InvalidTokenOffsetsException thrown if any token's endOffset exceeds the provided
* text's length
*/
public final String getBestFragments(
TokenStream tokenStream, String text, int maxNumFragments, String separator)
throws IOException, InvalidTokenOffsetsException {
String[] sections = getBestFragments(tokenStream, text, maxNumFragments);
StringBuilder result = new StringBuilder();
for (int i = 0; i < sections.length; i++) {
if (i > 0) {
result.append(separator);
}
result.append(sections[i]);
}
return result.toString();
}
public int getMaxDocCharsToAnalyze() {
return maxDocCharsToAnalyze;
}
public void setMaxDocCharsToAnalyze(int maxDocCharsToAnalyze) {
this.maxDocCharsToAnalyze = maxDocCharsToAnalyze;
}
public Fragmenter getTextFragmenter() {
return textFragmenter;
}
public void setTextFragmenter(Fragmenter fragmenter) {
textFragmenter = Objects.requireNonNull(fragmenter);
}
/**
* @return Object used to score each text fragment
*/
public Scorer getFragmentScorer() {
return fragmentScorer;
}
public void setFragmentScorer(Scorer scorer) {
fragmentScorer = Objects.requireNonNull(scorer);
}
public Encoder getEncoder() {
return encoder;
}
public void setEncoder(Encoder encoder) {
this.encoder = Objects.requireNonNull(encoder);
}
/**
* Throws an IllegalArgumentException with the provided message if 'argument' is null.
*
* @param argument the argument to be null-checked
* @param message the message of the exception thrown if argument == null
*/
private static void ensureArgumentNotNull(Object argument, String message) {
if (argument == null) {
throw new IllegalArgumentException(message);
}
}
static class FragmentQueue extends PriorityQueue {
FragmentQueue(int size) {
super(size);
}
@Override
public final boolean lessThan(TextFragment fragA, TextFragment fragB) {
if (fragA.getScore() == fragB.getScore()) return fragA.fragNum > fragB.fragNum;
else return fragA.getScore() < fragB.getScore();
}
}
}