Contrib: another highlighter approach
-------------------------------------
Key: LUCENE-644
URL: http://issues.apache.org/jira/browse/LUCENE-644
Project: Lucene - Java
Issue Type: Improvement
Components: Other
Reporter: Ronnie Kolehmainen
Priority: Minor
Attachments: FulltextHighlighter.java
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 TokenSources.java):
TermFreqVector tfv = (TermFreqVector) reader.getTermFreqVector(docId,
field);
if (tfv != null && tfv instanceof TermPositionVector)
{
// use FulltextHighlighter
}
else
{
// use standard Highlighter
}
Someone else might find this useful so I'm posting the code here.
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