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From Mark Miller <markrmil...@gmail.com>
Subject Re: Bug in Lucene 2.2.0 code? Simple code included (StringIndexOutOfBoundsException).
Date Sun, 05 Aug 2007 21:12:32 GMT
Its questionable if you are losing performance. Unless you have really 
large docs or a nasty slow analyzer, I have found it is usually faster 
or as fast to reanalyze as it is to use TermVectors, which can be quite 
time consuming to load up and assemble a TokenStream from. You might run 
some tests and see for yourself. I was quite surprised.

Also, perhaps things could be fixed in offset handling code for adding 
multiple fields. That might get you going. I am still not sure that they 
are just not handled correctly because it doesnt make sense to try, or 
what. But it seems to me they are being handled pretty badly now in 
terms of offsets. I honestly have not decided if its worth the effort to 
investigate further. I certainly would have, but am very busy working on 
a move. I know you can get the same results using other attacks, so it 
might just not be worth it.

Good luck.

- Mark

Lukas Vlcek wrote:
> Mark,
>
> thanks a lot. Based on my first tests it seems that I will be able to finish
> my initial goal.
> I will be doing something like the following:
>
>             for (int i = 0; i < hits.length(); i++) {
>
>                 String[] texts = hits.doc(i).getValues("lotid");
>
>                 for (String text: texts) {
>
>                     TokenStream tokenStream = analyzer.tokenStream("lotid",
> new StringReader(text));
>                     String result = highlighter.getBestFragment
> (tokenStream,text);
>
>                 }
>             }
>
> This works very well for me. The only disadvantage is that I can use neither
> term vector not positioning information thus I am loosing performance I
> guess.
>
> Thanks,
> Lukas
>
> On 7/30/07, Mark Miller <markrmiller@gmail.com> wrote:
>   
>> Hey Lukas,
>>
>> I was being simplistic when I said that the text and TokenSteam must be
>> exactly the same. It's difficult to think of a reason why you would not
>> want them to be the same though. Each Token records the offsets where it
>> can be found in the original text -- that is how the Highlighter knows
>> where to highlight in the original text with the only the Tokens to
>> inspect. So if a Token is scored >0, then the offsets for that Token
>> must be valid indexes into the text String (In the case of the
>> HTMLFormmatter, which only marks Tokens that score >0).
>>
>> Now an issue I see you having:
>>
>> The TokenStream for "example long text" is:
>> (term,startoffset,endoffset)
>>
>> (example,0,7)
>> (long,8,12)
>> (text,13,17)
>>
>> So for the query "example long" the Highlighter will highlight offsets
>> 0-7 and 8-12 in the source text. In your example, with the text only
>> being "example", the attempt to highlight the Token "long" will index
>> into the source text 8 and cause an outofbounds.
>>
>> In your case you are even worse off because you are building the
>> TokenStream from a field that was added more than once. This gives you
>> seemingly wrong offsets of:
>>
>> (example,0,7)
>> (long,14,18)
>> (text,22,26)
>>
>> Each word has its space accounted for twice. Maybe there is a reason for
>> this, but it looks wrong. I have not investigated enough to know if
>> TokenSources is responsible for this, or if core Lucene is the culprit.
>> Even if it was done differently though, there would still seem to be
>> possible issues with the possible spacing between words when you are
>> adding the words one at a time with no spacing in the same field.
>>
>> Looking at your original email though, you may be trying to do something
>> that is best done without the Highlighter.
>>
>> In summary , you should use Document.getFields (more efficient if you
>> are getting more than one field anyway) and get around the offset issues
>> above.
>>
>> - Mark
>>
>> Lukas Vlcek wrote:
>>     
>>> Mark,
>>> thank you for this. I will wait for your other responses.
>>> This will keep me going on :-)
>>>
>>> I didn't know that there is a design restriction in Lucene that the text
>>>       
>> and
>>     
>>> TokenStream must be exactly the same (still this seems redundant, I will
>>> dive into Lucene API more).
>>>
>>> BR
>>> Lukas
>>>
>>> On 7/29/07, Mark Miller <markrmiller@gmail.com> wrote:
>>>
>>>       
>>>> I'm am going to try and write up some more info for you tomorrow, but
>>>> just to point out: I do think there is a bug in the way offsets are
>>>> being handled. I don't think this is causing your current problem (what
>>>> I mentioned is) but it will prob cause you problems down the road. I
>>>> will look into this further.
>>>>
>>>> - Mark
>>>>
>>>> Lukas Vlcek wrote:
>>>>
>>>>         
>>>>> Hi Lucene experts,
>>>>>
>>>>> The following is a simple Lucene code which generates
>>>>> StringIndexOutOfBoundsException exception. I am using Lucene
>>>>>           
>> 2.2.0official
>>     
>>>>> releasse. Can anyone tell me what is wrong with this code? Is this a
>>>>>           
>> bug
>>     
>>>> or
>>>>
>>>>         
>>>>> a feature of Lucene? Any comments/hits highly welcommed!
>>>>>
>>>>> In a nutshell I have a document with two (or four) fileds:
>>>>> 1) all
>>>>> 2-4) small
>>>>>
>>>>> I use [all] for searching and [small] for highlighting.
>>>>>
>>>>> [packkage and imports truncated...]
>>>>>
>>>>> public class MemoryIndexCase {
>>>>>     static public void main(String[] arg) {
>>>>>
>>>>>         Document doc = new Document();
>>>>>
>>>>>         doc.add(new Field("all","example long text",
>>>>>                 Field.Store.NO, Field.Index.TOKENIZED));
>>>>>         doc.add(new Field("small","example",
>>>>>                 Field.Store.YES, Field.Index.UN_TOKENIZED,
>>>>> Field.TermVector.WITH_POSITIONS_OFFSETS));
>>>>>         doc.add(new Field("small","long",
>>>>>                 Field.Store.YES, Field.Index.UN_TOKENIZED,
>>>>> Field.TermVector.WITH_POSITIONS_OFFSETS));
>>>>>         doc.add(new Field("small","text",
>>>>>                 Field.Store.YES, Field.Index.UN_TOKENIZED,
>>>>> Field.TermVector.WITH_POSITIONS_OFFSETS));
>>>>>
>>>>>         try {
>>>>>             Directory idx = new RAMDirectory();
>>>>>             IndexWriter writer = new IndexWriter(idx, new
>>>>> StandardAnalyzer(), true);
>>>>>
>>>>>             writer.addDocument(doc);
>>>>>             writer.optimize();
>>>>>             writer.close();
>>>>>
>>>>>             Searcher searcher = new IndexSearcher(idx);
>>>>>
>>>>>             QueryParser qp = new QueryParser("all", new
>>>>>
>>>>>           
>>>> StandardAnalyzer());
>>>>
>>>>         
>>>>>             Query query = qp.parse("example text");
>>>>>             Hits hits = searcher.search(query);
>>>>>
>>>>>             Highlighter highlighter =    new Highlighter(new
>>>>> QueryScorer(query));
>>>>>
>>>>>             IndexReader ir = IndexReader.open(idx);
>>>>>             for (int i = 0; i < hits.length(); i++) {
>>>>>
>>>>>                 String text = hits.doc(i).get("small");
>>>>>
>>>>>                 TermFreqVector tfv = ir.getTermFreqVector(hits.id(i),
>>>>> "small");
>>>>>                 TokenStream tokenStream=
>>>>> TokenSources.getTokenStream((TermPositionVector)
>>>>> tfv);
>>>>>
>>>>>                 String result =
>>>>>                     highlighter.getBestFragment(tokenStream,text);
>>>>>                 System.out.println(result);
>>>>>             }
>>>>>
>>>>>         } catch (Throwable e) {
>>>>>             e.printStackTrace();
>>>>>         }
>>>>>     }
>>>>> }
>>>>>
>>>>> The exception is:
>>>>> java.lang.StringIndexOutOfBoundsException: String index out of range:
>>>>>           
>> 11
>>     
>>>>>     at java.lang.String.substring(String.java:1935)
>>>>>     at
>>>>>
>>>>>           
>>>> org.apache.lucene.search.highlight.Highlighter.getBestTextFragments(
>>>>
>>>>         
>>>>> Highlighter.java:235)
>>>>>     at org.apache.lucene.search.highlight.Highlighter.getBestFragments
>>>>>           
>> (
>>     
>>>>> Highlighter.java:175)
>>>>>     at org.apache.lucene.search.highlight.Highlighter.getBestFragment(
>>>>> Highlighter.java:101)
>>>>>     at org.lucenetest.MemoryIndexCase.main(MemoryIndexCase.java:70)
>>>>>
>>>>> Best regards,
>>>>> Lukas
>>>>>
>>>>>
>>>>>
>>>>>           
>>>> ---------------------------------------------------------------------
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>>>>
>>>>
>>>>
>>>>         
>>>       
>> ---------------------------------------------------------------------
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>>
>>
>>     
>
>   

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