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## org.apache.lucene.search.postingshighlight
Class PostingsHighlighter

    java.lang.Object
      org.apache.lucene.search.postingshighlight.PostingsHighlighter

    public class PostingsHighlighter

extends Object

Simple highlighter that does not analyze fields nor use term vectors. Instead it requires `FieldInfo.IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS`.

PostingsHighlighter 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`.

WARNING: The code is very new and probably still has some exciting bugs!

Example usage:

       // configure field with offsets at index time
       FieldType offsetsType = new FieldType(TextField.TYPE_STORED);
       offsetsType.setIndexOptions(IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS);
       Field body = new Field("body", "foobar", offsetsType);

       // retrieve highlights at query time
       PostingsHighlighter highlighter = new PostingsHighlighter();
       Query query = new TermQuery(new Term("body", "highlighting"));
       TopDocs topDocs = searcher.search(query, n);
       String highlights[] = highlighter.highlight("body", query, searcher, topDocs);

This is thread-safe, and can be used across different readers.

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

Field Summary
`static int` | `DEFAULT_MAX_LENGTH` Default maximum content size to process.

Constructor Summary
`PostingsHighlighter()` Creates a new highlighter with default parameters.
`PostingsHighlighter(int maxLength)` Creates a new highlighter, specifying maximum content length.

Method Summary
`protected BreakIterator` | `getBreakIterator(String field)` Returns the `BreakIterator` to use for dividing text into passages.
`protected Passage[]` | `getEmptyHighlight(String fieldName, BreakIterator bi, int maxPassages)` Called to summarize a document when no hits were found.
`protected PassageFormatter` | `getFormatter(String field)` Returns the `PassageFormatter` to use for formatting passages into highlighted snippets.
`protected PassageScorer` | `getScorer(String field)` Returns the `PassageScorer` to use for ranking passages.
`String[]` | `highlight(String field, Query query, IndexSearcher searcher, TopDocs topDocs)` Highlights the top passages from a single field.
`String[]` | `highlight(String field, Query query, IndexSearcher searcher, TopDocs topDocs, int maxPassages)` Highlights the top-N passages from a single field.
`Map<String,String[]>` | `highlightFields(String[] fieldsIn, Query query, IndexSearcher searcher, 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, IndexSearcher searcher, TopDocs topDocs)` Highlights the top passages from multiple fields.
`Map<String,String[]>` | `highlightFields(String[] fields, Query query, IndexSearcher searcher, TopDocs topDocs, int[] maxPassages)` Highlights the top-N passages from multiple fields.
`protected String[][]` | `loadFieldValues(IndexSearcher searcher, String[] fields, int[] docids, int maxLength)` Loads the String values for each field X docID to be highlighted.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### DEFAULT_MAX_LENGTH

    public static final int DEFAULT_MAX_LENGTH

  Default maximum content size to process. Typically snippets closer to the beginning of the document better summarize its content

  See Also:
    Constant Field Values

Constructor Detail

### PostingsHighlighter

    public PostingsHighlighter()

  Creates a new highlighter with default parameters.

### PostingsHighlighter

    public PostingsHighlighter(int maxLength)

  Creates a new highlighter, specifying maximum content length.

  Parameters:
    `maxLength` - maximum content size to process.
  Throws:
    `IllegalArgumentException` - if `maxLength` is negative or `Integer.MAX_VALUE`

Method Detail

### 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.

### 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.

### 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.

### highlight

    public String[] highlight(String field,
                              Query query,
                              IndexSearcher searcher,
                              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.
    `searcher` - searcher that was previously used to execute the query.
    `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 `FieldInfo.IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS`

### highlight

    public String[] highlight(String field,
                              Query query,
                              IndexSearcher searcher,
                              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 and also be indexed with offsets.
    `query` - query to highlight.
    `searcher` - searcher that was previously used to execute the query.
    `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 `FieldInfo.IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS`

### highlightFields

    public Map<String,String[]> highlightFields(String[] fields,
                                                Query query,
                                                IndexSearcher searcher,
                                                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, searcher, topDocs));
       }
       return m;

  Parameters:
    `fields` - field names to highlight. Must have a stored string value and also be indexed with offsets.
    `query` - query to highlight.
    `searcher` - searcher that was previously used to execute the query.
    `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 `FieldInfo.IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS`

### highlightFields

    public Map<String,String[]> highlightFields(String[] fields,
                                                Query query,
                                                IndexSearcher searcher,
                                                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, searcher, topDocs, maxPassages));
       }
       return m;

  Parameters:
    `fields` - field names to highlight. Must have a stored string value and also be indexed with offsets.
    `query` - query to highlight.
    `searcher` - searcher that was previously used to execute the query.
    `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 `FieldInfo.IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS`

### highlightFields

    public Map<String,String[]> highlightFields(String[] fieldsIn,
                                                Query query,
                                                IndexSearcher searcher,
                                                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 and also be indexed with offsets.
    `query` - query to highlight.
    `searcher` - searcher that was previously used to execute the query.
    `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 `topDocs`. 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 `FieldInfo.IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS`

### loadFieldValues

    protected String[][] loadFieldValues(IndexSearcher searcher,
                                         String[] fields,
                                         int[] docids,
                                         int maxLength)
                                  throws IOException

  Loads the String values for each field X docID to be highlighted. By default this loads from stored fields, but a subclass can change the source. This method should allocate the String[fields.length][docids.length] and fill all values. The returned Strings must be identical to what was indexed.

  Throws:
    `IOException`

### getEmptyHighlight

    protected Passage[] getEmptyHighlight(String fieldName,
                                          BreakIterator bi,
                                          int maxPassages)

  Called to summarize a document when no hits were found. By default this just returns the first `maxPassages` sentences; subclasses can override to customize.

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