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From "Ronnie Kolehmainen (JIRA)" <>
Subject [jira] Created: (LUCENE-644) Contrib: another highlighter approach
Date Wed, 02 Aug 2006 07:54:13 GMT
Contrib: another highlighter approach

                 Key: LUCENE-644
             Project: Lucene - Java
          Issue Type: Improvement
          Components: Other
            Reporter: Ronnie Kolehmainen
            Priority: Minor

Mark Harwoods highlighter package is a great contribution to Lucene, I've used it a lot! However,
when you have *large* documents (fields), highlighting can be quite time consuming if you
increase the number of bytes to analyze with setMaxDocBytesToAnalyze(int). The default value
of 50k is often too low for indexed PDFs etcetera, which results in empty highlight strings.

This is an alternative approach using term position vectors only to build fragment info objects.
Then a StringReader can read the relevant fragments and skip() between them. This is a lot
faster. Also, this method uses the *entire* field for finding the best fragments so you're
always guaranteed to get a highlight snippet.

Because this method only works with fields which have term positions stored one can check
if this method works for a particular field using following code (taken from

        TermFreqVector tfv = (TermFreqVector) reader.getTermFreqVector(docId, field);
        if (tfv != null && tfv instanceof TermPositionVector)
          // use FulltextHighlighter
          // use standard Highlighter

Someone else might find this useful so I'm posting the code here.

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