org.apache.lucene.search.uhighlight

Class UnifiedHighlighter

java.lang.Object

org.apache.lucene.search.uhighlight.UnifiedHighlighter

public class UnifiedHighlighter
extends Object

A Highlighter that can get offsets from either postings (IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS), term vectors (FieldType.setStoreTermVectorOffsets(boolean)), or via re-analyzing text.

This highlighter treats the single original document as the whole corpus, and then scores individual passages as if they were documents in this corpus. It uses a BreakIterator to find passages in the text; by default it breaks using getSentenceInstance(Locale.ROOT). It then iterates in parallel (merge sorting by offset) through the positions of all terms from the query, coalescing those hits that occur in a single passage into a Passage, and then scores each Passage using a separate PassageScorer. Passages are finally formatted into highlighted snippets with a PassageFormatter.

You can customize the behavior by calling some of the setters, or by subclassing and overriding some methods. Some important hooks:

• getBreakIterator(String): Customize how the text is divided into passages.
• getScorer(String): Customize how passages are ranked.
• getFormatter(String): Customize how snippets are formatted.

This is thread-safe.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	UnifiedHighlighter.HighlightFlag Flags for controlling highlighting behavior.
protected static class	UnifiedHighlighter.LimitedStoredFieldVisitor Fetches stored fields for highlighting.
static class	UnifiedHighlighter.OffsetSource Source of term offsets; essential for highlighting.

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_CACHE_CHARS_THRESHOLD
static int	DEFAULT_MAX_LENGTH
protected FieldInfos	fieldInfos
protected Analyzer	indexAnalyzer
protected static char	MULTIVAL_SEP_CHAR
protected IndexSearcher	searcher
protected static CharacterRunAutomaton[]	ZERO_LEN_AUTOMATA_ARRAY

Constructor Summary

Constructors

Constructor and Description
UnifiedHighlighter(IndexSearcher indexSearcher, Analyzer indexAnalyzer) Constructs the highlighter with the given index searcher and analyzer.

Method Summary

Modifier and Type	Method and Description
protected static Set<Term>	extractTerms(Query query) Extracts matching terms after rewriting against an empty index
protected static BytesRef[]	filterExtractedTerms(Predicate<String> fieldMatcher, Set<Term> queryTerms)
protected CharacterRunAutomaton[]	getAutomata(String field, Query query, Set<UnifiedHighlighter.HighlightFlag> highlightFlags)
protected BreakIterator	getBreakIterator(String field) Returns the BreakIterator to use for dividing text into passages.
int	getCacheFieldValCharsThreshold() Limits the amount of field value pre-fetching until this threshold is passed.
protected FieldHighlighter	getFieldHighlighter(String field, Query query, Set<Term> allTerms, int maxPassages)
protected FieldInfo	getFieldInfo(String field) Called by the default implementation of getOffsetSource(String).
protected Predicate<String>	getFieldMatcher(String field) Returns the predicate to use for extracting the query part that must be highlighted.
protected Set<UnifiedHighlighter.HighlightFlag>	getFlags(String field)
protected PassageFormatter	getFormatter(String field) Returns the PassageFormatter to use for formatting passages into highlighted snippets.
Analyzer	getIndexAnalyzer() ...
IndexSearcher	getIndexSearcher() ...
int	getMaxLength() The maximum content size to process.
protected int	getMaxNoHighlightPassages(String field) Returns the number of leading passages (as delineated by the BreakIterator) when no highlights could be found.
protected UnifiedHighlighter.OffsetSource	getOffsetSource(String field) Determine the offset source for the specified field.
protected FieldOffsetStrategy	getOffsetStrategy(UnifiedHighlighter.OffsetSource offsetSource, UHComponents components)
protected UnifiedHighlighter.OffsetSource	getOptimizedOffsetSource(String field, BytesRef[] terms, PhraseHelper phraseHelper, CharacterRunAutomaton[] automata)
protected PhraseHelper	getPhraseHelper(String field, Query query, Set<UnifiedHighlighter.HighlightFlag> highlightFlags)
protected PassageScorer	getScorer(String field) Returns the PassageScorer to use for ranking passages.
String[]	highlight(String field, Query query, TopDocs topDocs) Highlights the top passages from a single field.
String[]	highlight(String field, Query query, TopDocs topDocs, int maxPassages) Highlights the top-N passages from a single field.
Map<String,String[]>	highlightFields(String[] fieldsIn, Query query, int[] docidsIn, int[] maxPassagesIn) Highlights the top-N passages from multiple fields, for the provided int[] docids.
Map<String,String[]>	highlightFields(String[] fields, Query query, TopDocs topDocs) Highlights the top passages from multiple fields.
Map<String,String[]>	highlightFields(String[] fields, Query query, TopDocs topDocs, int[] maxPassages) Highlights the top-N passages from multiple fields.
protected Map<String,Object[]>	highlightFieldsAsObjects(String[] fieldsIn, Query query, int[] docIdsIn, int[] maxPassagesIn) Expert: highlights the top-N passages from multiple fields, for the provided int[] docids, to custom Object as returned by the PassageFormatter.
Object	highlightWithoutSearcher(String field, Query query, String content, int maxPassages) Highlights text passed as a parameter.
protected List<CharSequence[]>	loadFieldValues(String[] fields, DocIdSetIterator docIter, int cacheCharsThreshold) Loads the String values for each docId by field to be highlighted.
protected UnifiedHighlighter.LimitedStoredFieldVisitor	newLimitedStoredFieldsVisitor(String[] fields)
protected Collection<Query>	preSpanQueryRewrite(Query query) When highlighting phrases accurately, we may need to handle custom queries that aren't supported in the WeightedSpanTermExtractor as called by the PhraseHelper.
protected Boolean	requiresRewrite(SpanQuery spanQuery) When highlighting phrases accurately, we need to know which SpanQuery's need to have Query.rewrite(IndexReader) called on them.
void	setBreakIterator(Supplier<BreakIterator> breakIterator)
void	setCacheFieldValCharsThreshold(int cacheFieldValCharsThreshold)
void	setFieldMatcher(Predicate<String> predicate)
void	setFormatter(PassageFormatter formatter)
void	setHandleMultiTermQuery(boolean handleMtq)
void	setHighlightPhrasesStrictly(boolean highlightPhrasesStrictly)
void	setMaxLength(int maxLength)
void	setMaxNoHighlightPassages(int defaultMaxNoHighlightPassages)
void	setScorer(PassageScorer scorer)
protected boolean	shouldHandleMultiTermQuery(String field) Returns whether MultiTermQuery derivatives will be highlighted.
protected boolean	shouldHighlightPhrasesStrictly(String field) Returns whether position sensitive queries (e.g.
protected boolean	shouldPreferPassageRelevancyOverSpeed(String field)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

MULTIVAL_SEP_CHAR

protected static final char MULTIVAL_SEP_CHAR

See Also:

Constant Field Values

DEFAULT_MAX_LENGTH

public static final int DEFAULT_MAX_LENGTH

See Also:

Constant Field Values

DEFAULT_CACHE_CHARS_THRESHOLD

public static final int DEFAULT_CACHE_CHARS_THRESHOLD

See Also:

Constant Field Values

ZERO_LEN_AUTOMATA_ARRAY

protected static final CharacterRunAutomaton[] ZERO_LEN_AUTOMATA_ARRAY

searcher

protected final IndexSearcher searcher

indexAnalyzer

protected final Analyzer indexAnalyzer

fieldInfos

protected volatile FieldInfos fieldInfos

Constructor Detail

UnifiedHighlighter

public UnifiedHighlighter(IndexSearcher indexSearcher,
                          Analyzer indexAnalyzer)

Constructs the highlighter with the given index searcher and analyzer.

Parameters:

indexSearcher - Usually required, unless highlightWithoutSearcher(String, Query, String, int) is used, in which case this needs to be null.

indexAnalyzer - Required, even if in some circumstances it isn't used.

Method Detail

extractTerms

protected static Set<Term> extractTerms(Query query)
                                 throws IOException

Extracts matching terms after rewriting against an empty index

Throws:

IOException

setHandleMultiTermQuery

public void setHandleMultiTermQuery(boolean handleMtq)

setHighlightPhrasesStrictly

public void setHighlightPhrasesStrictly(boolean highlightPhrasesStrictly)

setMaxLength

public void setMaxLength(int maxLength)

setBreakIterator

public void setBreakIterator(Supplier<BreakIterator> breakIterator)

setScorer

public void setScorer(PassageScorer scorer)

setFormatter

public void setFormatter(PassageFormatter formatter)

setMaxNoHighlightPassages

public void setMaxNoHighlightPassages(int defaultMaxNoHighlightPassages)

setCacheFieldValCharsThreshold

public void setCacheFieldValCharsThreshold(int cacheFieldValCharsThreshold)

setFieldMatcher

public void setFieldMatcher(Predicate<String> predicate)

shouldHandleMultiTermQuery

protected boolean shouldHandleMultiTermQuery(String field)

Returns whether MultiTermQuery derivatives will be highlighted. By default it's enabled. MTQ highlighting can be expensive, particularly when using offsets in postings.

shouldHighlightPhrasesStrictly

protected boolean shouldHighlightPhrasesStrictly(String field)

Returns whether position sensitive queries (e.g. phrases and SpanQueryies) should be highlighted strictly based on query matches (slower) versus any/all occurrences of the underlying terms. By default it's enabled, but there's no overhead if such queries aren't used.

shouldPreferPassageRelevancyOverSpeed

protected boolean shouldPreferPassageRelevancyOverSpeed(String field)

getFieldMatcher

protected Predicate<String> getFieldMatcher(String field)

Returns the predicate to use for extracting the query part that must be highlighted. By default only queries that target the current field are kept. (AKA requireFieldMatch)

getMaxLength

public int getMaxLength()

The maximum content size to process. Content will be truncated to this size before highlighting. Typically snippets closer to the beginning of the document better summarize its content.

getBreakIterator

protected BreakIterator getBreakIterator(String field)

Returns the BreakIterator to use for dividing text into passages. This returns BreakIterator.getSentenceInstance(Locale) by default; subclasses can override to customize.

Note: this highlighter will call BreakIterator.preceding(int) and BreakIterator.next() many times on it. The default generic JDK implementation of preceding performs poorly.

getScorer

protected PassageScorer getScorer(String field)

Returns the PassageScorer to use for ranking passages. This returns a new PassageScorer by default; subclasses can override to customize.

getFormatter

protected PassageFormatter getFormatter(String field)

Returns the PassageFormatter to use for formatting passages into highlighted snippets. This returns a new PassageFormatter by default; subclasses can override to customize.

getMaxNoHighlightPassages

protected int getMaxNoHighlightPassages(String field)

Returns the number of leading passages (as delineated by the BreakIterator) when no highlights could be found. If it's less than 0 (the default) then this defaults to the maxPassages parameter given for each request. If this is 0 then the resulting highlight is null (not formatted).

getCacheFieldValCharsThreshold

public int getCacheFieldValCharsThreshold()

Limits the amount of field value pre-fetching until this threshold is passed. The highlighter internally highlights in batches of documents sized on the sum field value length (in chars) of the fields to be highlighted (bounded by getMaxLength() for each field). By setting this to 0, you can force documents to be fetched and highlighted one at a time, which you usually shouldn't do. The default is 524288 chars which translates to about a megabyte. However, note that the highlighter sometimes ignores this and highlights one document at a time (without caching a bunch of documents in advance) when it can detect there's no point in it -- such as when all fields will be highlighted via re-analysis as one example.

getIndexSearcher

public IndexSearcher getIndexSearcher()

... as passed in from constructor.

getIndexAnalyzer

public Analyzer getIndexAnalyzer()

... as passed in from constructor.

getOffsetSource

protected UnifiedHighlighter.OffsetSource getOffsetSource(String field)

Determine the offset source for the specified field. The default algorithm is as follows:

1. This calls getFieldInfo(String). Note this returns null if there is no searcher or if the field isn't found there.
2. If there's a field info it has IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS then UnifiedHighlighter.OffsetSource.POSTINGS is returned.
3. If there's a field info and FieldInfo.hasVectors() then UnifiedHighlighter.OffsetSource.TERM_VECTORS is returned (note we can't check here if the TV has offsets; if there isn't then an exception will get thrown down the line).
4. Fall-back: UnifiedHighlighter.OffsetSource.ANALYSIS is returned.

Note that the highlighter sometimes switches to something else based on the query, such as if you have UnifiedHighlighter.OffsetSource.POSTINGS_WITH_TERM_VECTORS but in fact don't need term vectors.

getFieldInfo

protected FieldInfo getFieldInfo(String field)

Called by the default implementation of getOffsetSource(String). If there is no searcher then we simply always return null.

highlight

public String[] highlight(String field,
                          Query query,
                          TopDocs topDocs)
                   throws IOException

Highlights the top passages from a single field.

Parameters:

field - field name to highlight. Must have a stored string value and also be indexed with offsets.

query - query to highlight.

topDocs - TopDocs containing the summary result documents to highlight.

Returns:

Array of formatted snippets corresponding to the documents in topDocs. If no highlights were found for a document, the first sentence for the field will be returned.

Throws:

IOException - if an I/O error occurred during processing

IllegalArgumentException - if field was indexed without IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS

highlight

public String[] highlight(String field,
                          Query query,
                          TopDocs topDocs,
                          int maxPassages)
                   throws IOException

Highlights the top-N passages from a single field.

Parameters:

field - field name to highlight. Must have a stored string value.

query - query to highlight.

topDocs - TopDocs containing the summary result documents to highlight.

maxPassages - The maximum number of top-N ranked passages used to form the highlighted snippets.

Returns:

Array of formatted snippets corresponding to the documents in topDocs. If no highlights were found for a document, the first maxPassages sentences from the field will be returned.

Throws:

IOException - if an I/O error occurred during processing

IllegalArgumentException - if field was indexed without IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS

highlightFields

public Map<String,String[]> highlightFields(String[] fields,
                                            Query query,
                                            TopDocs topDocs)
                                     throws IOException

Highlights the top passages from multiple fields.

Conceptually, this behaves as a more efficient form of:

 Map m = new HashMap();
 for (String field : fields) {
 m.put(field, highlight(field, query, topDocs));
 }
 return m;
 

Parameters:

fields - field names to highlight. Must have a stored string value.

query - query to highlight.

topDocs - TopDocs containing the summary result documents to highlight.

Returns:

Map keyed on field name, containing the array of formatted snippets corresponding to the documents in topDocs. If no highlights were found for a document, the first sentence from the field will be returned.

Throws:

IOException - if an I/O error occurred during processing

IllegalArgumentException - if field was indexed without IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS

highlightFields

public Map<String,String[]> highlightFields(String[] fields,
                                            Query query,
                                            TopDocs topDocs,
                                            int[] maxPassages)
                                     throws IOException

Highlights the top-N passages from multiple fields.

Conceptually, this behaves as a more efficient form of:

 Map m = new HashMap();
 for (String field : fields) {
 m.put(field, highlight(field, query, topDocs, maxPassages));
 }
 return m;
 

Parameters:

fields - field names to highlight. Must have a stored string value.

query - query to highlight.

topDocs - TopDocs containing the summary result documents to highlight.

maxPassages - The maximum number of top-N ranked passages per-field used to form the highlighted snippets.

Returns:

Map keyed on field name, containing the array of formatted snippets corresponding to the documents in topDocs. If no highlights were found for a document, the first maxPassages sentences from the field will be returned.

Throws:

IOException - if an I/O error occurred during processing

IllegalArgumentException - if field was indexed without IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS

highlightFields

public Map<String,String[]> highlightFields(String[] fieldsIn,
                                            Query query,
                                            int[] docidsIn,
                                            int[] maxPassagesIn)
                                     throws IOException

Highlights the top-N passages from multiple fields, for the provided int[] docids.

Parameters:

fieldsIn - field names to highlight. Must have a stored string value.

query - query to highlight.

docidsIn - containing the document IDs to highlight.

maxPassagesIn - The maximum number of top-N ranked passages per-field used to form the highlighted snippets.

Returns:

Map keyed on field name, containing the array of formatted snippets corresponding to the documents in docidsIn. If no highlights were found for a document, the first maxPassages from the field will be returned.

Throws:

IOException - if an I/O error occurred during processing

IllegalArgumentException - if field was indexed without IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS

highlightFieldsAsObjects

protected Map<String,Object[]> highlightFieldsAsObjects(String[] fieldsIn,
                                                        Query query,
                                                        int[] docIdsIn,
                                                        int[] maxPassagesIn)
                                                 throws IOException

Expert: highlights the top-N passages from multiple fields, for the provided int[] docids, to custom Object as returned by the PassageFormatter. Use this API to render to something other than String.

Parameters:

fieldsIn - field names to highlight. Must have a stored string value.

query - query to highlight.

docIdsIn - containing the document IDs to highlight.

maxPassagesIn - The maximum number of top-N ranked passages per-field used to form the highlighted snippets.

Returns:

Map keyed on field name, containing the array of formatted snippets corresponding to the documents in docIdsIn. If no highlights were found for a document, the first maxPassages from the field will be returned.

Throws:

IOException - if an I/O error occurred during processing

IllegalArgumentException - if field was indexed without IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS

highlightWithoutSearcher

public Object highlightWithoutSearcher(String field,
                                       Query query,
                                       String content,
                                       int maxPassages)
                                throws IOException

Highlights text passed as a parameter. This requires the IndexSearcher provided to this highlighter is null. This use-case is more rare. Naturally, the mode of operation will be UnifiedHighlighter.OffsetSource.ANALYSIS. The result of this method is whatever the PassageFormatter returns. For the DefaultPassageFormatter and assuming content has non-zero length, the result will be a non-null string -- so it's safe to call Object.toString() on it in that case.

Parameters:

field - field name to highlight (as found in the query).

query - query to highlight.

content - text to highlight.

maxPassages - The maximum number of top-N ranked passages used to form the highlighted snippets.

Returns:

result of the PassageFormatter -- probably a String. Might be null.

Throws:

IOException - if an I/O error occurred during processing

getFieldHighlighter

protected FieldHighlighter getFieldHighlighter(String field,
                                               Query query,
                                               Set<Term> allTerms,
                                               int maxPassages)

filterExtractedTerms

protected static BytesRef[] filterExtractedTerms(Predicate<String> fieldMatcher,
                                                 Set<Term> queryTerms)

getFlags

protected Set<UnifiedHighlighter.HighlightFlag> getFlags(String field)

getPhraseHelper

protected PhraseHelper getPhraseHelper(String field,
                                       Query query,
                                       Set<UnifiedHighlighter.HighlightFlag> highlightFlags)

getAutomata

protected CharacterRunAutomaton[] getAutomata(String field,
                                              Query query,
                                              Set<UnifiedHighlighter.HighlightFlag> highlightFlags)

getOptimizedOffsetSource

protected UnifiedHighlighter.OffsetSource getOptimizedOffsetSource(String field,
                                                                   BytesRef[] terms,
                                                                   PhraseHelper phraseHelper,
                                                                   CharacterRunAutomaton[] automata)

getOffsetStrategy

protected FieldOffsetStrategy getOffsetStrategy(UnifiedHighlighter.OffsetSource offsetSource,
                                                UHComponents components)

requiresRewrite

protected Boolean requiresRewrite(SpanQuery spanQuery)

When highlighting phrases accurately, we need to know which SpanQuery's need to have Query.rewrite(IndexReader) called on them. It helps performance to avoid it if it's not needed. This method will be invoked on all SpanQuery instances recursively. If you have custom SpanQuery queries then override this to check instanceof and provide a definitive answer. If the query isn't your custom one, simply return null to have the default rules apply, which govern the ones included in Lucene.

preSpanQueryRewrite

protected Collection<Query> preSpanQueryRewrite(Query query)

When highlighting phrases accurately, we may need to handle custom queries that aren't supported in the WeightedSpanTermExtractor as called by the PhraseHelper. Should custom query types be needed, this method should be overriden to return a collection of queries if appropriate, or null if nothing to do. If the query is not custom, simply returning null will allow the default rules to apply.

Parameters:

query - Query to be highlighted

Returns:

A Collection of Query object(s) if needs to be rewritten, otherwise null.

loadFieldValues

protected List<CharSequence[]> loadFieldValues(String[] fields,
                                               DocIdSetIterator docIter,
                                               int cacheCharsThreshold)
                                        throws IOException

Loads the String values for each docId by field to be highlighted. By default this loads from stored fields by the same name as given, but a subclass can change the source. The returned Strings must be identical to what was indexed (at least for postings or term-vectors offset sources). This method must load fields for at least one document from the given DocIdSetIterator but need not return all of them; by default the character lengths are summed and this method will return early when cacheCharsThreshold is exceeded. Specifically if that number is 0, then only one document is fetched no matter what. Values in the array of CharSequence will be null if no value was found.

Throws:

IOException

newLimitedStoredFieldsVisitor

protected UnifiedHighlighter.LimitedStoredFieldVisitor newLimitedStoredFieldsVisitor(String[] fields)

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.