Hi,
I have a problem when using the Highlighter with N-GramAnalyzer and PhraseQuery:
Searching for a substring with length = N (4 in my case) yields the following
exception:
java.lang.IllegalArgumentException: Less than 2 subSpans.size():1
at
org.apache.lucene.search.spans.ConjunctionSpans.<init>(ConjunctionSpans.java:40)
at
org.apache.lucene.search.spans.NearSpansOrdered.<init>(NearSpansOrdered.java:56)
at
org.apache.lucene.search.spans.SpanNearQuery$SpanNearWeight.getSpans(SpanNearQuery.java:232)
at
org.apache.lucene.search.highlight.WeightedSpanTermExtractor.extractWeightedSpanTerms(WeightedSpanTermExtractor.java:292)
at
org.apache.lucene.search.highlight.WeightedSpanTermExtractor.extract(WeightedSpanTermExtractor.java:137)
at
org.apache.lucene.search.highlight.WeightedSpanTermExtractor.getWeightedSpanTerms(WeightedSpanTermExtractor.java:506)
at
org.apache.lucene.search.highlight.QueryScorer.initExtractor(QueryScorer.java:219)
at org.apache.lucene.search.highlight.QueryScorer.init(QueryScorer.java:187)
at
org.apache.lucene.search.highlight.Highlighter.getBestTextFragments(Highlighter.java:196)
Below is a JUnit-Test reproducing this behavior. In case of searching for a
string with more than N characters or using NGramPhraseQuery this problem
doesn't occur.
Why is it that more than 1 subSpans are required?
public class HighlighterTest {
@Rule
public final ExpectedException exception = ExpectedException.none();
@Test
public void testHighlighterWithPhraseQueryThrowsException() throws
IOException, InvalidTokenOffsetsException {
final Analyzer analyzer = new NGramAnalyzer(4);
final String fieldName = "substring";
final List<BytesRef> list = new ArrayList<>();
list.add(new BytesRef("uchu"));
final PhraseQuery query = new PhraseQuery(fieldName, list.toArray(new
BytesRef[list.size()]));
final QueryScorer fragmentScorer = new QueryScorer(query, fieldName);
final SimpleHTMLFormatter formatter = new SimpleHTMLFormatter("<b>",
"</b>");
exception.expect(IllegalArgumentException.class);
exception.expectMessage("Less than 2 subSpans.size():1");
final Highlighter highlighter = new
Highlighter(formatter,TextEncoder.NONE.getEncoder(), fragmentScorer);
highlighter.setTextFragmenter(new SimpleFragmenter(100));
final String fragment = highlighter.getBestFragment(analyzer,
fieldName, "Buchung");
assertEquals("B<b>uchu</b>ng",fragment);
}
public final class NGramAnalyzer extends Analyzer {
private final int minNGram;
public NGramAnalyzer(final int minNGram) {
super();
this.minNGram = minNGram;
}
@Override
protected TokenStreamComponents createComponents(final String fieldName) {
final Tokenizer source = new NGramTokenizer(minNGram, minNGram);
return new TokenStreamComponents(source);
}
}
}
Thanks and cheers,
Eva
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