SimpleSpanFragmenter fails to start a new fragment
--------------------------------------------------
Key: LUCENE-2229
URL: https://issues.apache.org/jira/browse/LUCENE-2229
Project: Lucene - Java
Issue Type: Bug
Components: contrib/highlighter
Reporter: Elmer Garduno
SimpleSpanFragmenter fails to identify a new fragment when there is more than
one stop word after a span is detected. This problem can be observed when the
Query contains a PhraseQuery.
The problem is that the span extends toward the end of the TokenGroup. This is
because {{waitForProps = positionSpans.get(i).end + 1;}} and {{position +=
posIncAtt.getPositionIncrement();}} this generates a value of {{position}}
greater than the value of {{waitForProps}} and {{(waitForPos == position)}}
never matches.
{code:title=SimpleSpanFragmenter.java}
public boolean isNewFragment() {
position += posIncAtt.getPositionIncrement();
if (waitForPos == position) {
waitForPos = -1;
} else if (waitForPos != -1) {
return false;
}
WeightedSpanTerm wSpanTerm =
queryScorer.getWeightedSpanTerm(termAtt.term());
if (wSpanTerm != null) {
List<PositionSpan> positionSpans = wSpanTerm.getPositionSpans();
for (int i = 0; i < positionSpans.size(); i++) {
if (positionSpans.get(i).start == position) {
waitForPos = positionSpans.get(i).end + 1;
break;
}
}
}
...
{code}
An example is provided in the test case for the following Document and the
query *"all tokens"* followed by the words _of a_.
{panel:title=Document}
"Attribute instances are reused for *all tokens* _of a_ document. Thus, a
TokenStream/-Filter needs to update the appropriate Attribute(s) in
incrementToken(). The consumer, commonly the Lucene indexer, consumes the data
in the Attributes and then calls incrementToken() again until it retuns false,
which indicates that the end of the stream was reached. This means that in each
call of incrementToken() a TokenStream/-Filter can safely overwrite the data in
the Attribute instances."
{panel}
{code:title=HighlighterTest.java}
public void testSimpleSpanFragmenter() throws Exception {
...
doSearching("\"all tokens\"");
maxNumFragmentsRequired = 2;
scorer = new QueryScorer(query, FIELD_NAME);
highlighter = new Highlighter(this, scorer);
for (int i = 0; i < hits.totalHits; i++) {
String text = searcher.doc(hits.scoreDocs[i].doc).get(FIELD_NAME);
TokenStream tokenStream = analyzer.tokenStream(FIELD_NAME, new
StringReader(text));
highlighter.setTextFragmenter(new SimpleSpanFragmenter(scorer, 20));
String result = highlighter.getBestFragments(tokenStream, text,
maxNumFragmentsRequired, "...");
System.out.println("\t" + result);
}
}
{code}
{panel:title=Result}
are reused for <B>all</B> <B>tokens</B> of a document. Thus, a
TokenStream/-Filter needs to update the appropriate Attribute(s) in
incrementToken(). The consumer, commonly the Lucene indexer, consumes the data
in the Attributes and then calls incrementToken() again until it retuns false,
which indicates that the end of the stream was reached. This means that in each
call of incrementToken() a TokenStream/-Filter can safely overwrite the data in
the Attribute instances.
{panel}
{panel:title=Expected Result}
for <B>all</B> <B>tokens</B> of a document
{panel}
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