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From "Hoss Man (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1422) New TokenStream API
Date Mon, 24 Nov 2008 01:35:44 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12650093#action_12650093
] 

Hoss Man commented on LUCENE-1422:
----------------------------------

FWIW: In previous versions of Lucene, a class like this would have been legal...

{code}
public final class DummyStream extends TokenFilter {
  int count = 5;
  public DummyStream() {  super(null);  }
  public final Token next() {
    return (0 < count--) ? new Token("YES", 0, 0) : null;
  }
  public void reset() throws IOException {count = 5}
  public void close() throws IOException {}
}
{code}

...there wouldn't have been much reason to write a subclass like this (better to subclass
TokenStream directly for this type of usecase), but it would have worked.  with the new AttributeSource
class, TokenFilter actually cares about the TokenStream constructor arg during construction,
and a constructor like this will cause a NullPointerException.

It's an esoteric enough possibility that we probably don't need to worry about it, but i'm
documenting it for posterity.  (I only noticed because Solr had a test case where it was constructing
a stock TokenFilter using a null "input" arg just to then test the object in other ways)

if anyone does run into a problem with something like this, your best solution is probably
to subclass TokenStream directly, it has a no arg constructor.

for searching...

{noformat}
java.lang.NullPointerException
	at org.apache.lucene.util.AttributeSource.<init>(AttributeSource.java:69)
	at org.apache.lucene.analysis.TokenStream.<init>(TokenStream.java:91)
	at org.apache.lucene.analysis.TokenFilter.<init>(TokenFilter.java:42)
	...
{noformat}

> New TokenStream API
> -------------------
>
>                 Key: LUCENE-1422
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1422
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: Analysis
>            Reporter: Michael Busch
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 2.9
>
>         Attachments: lucene-1422-take4.patch, lucene-1422-take5.patch, lucene-1422-take6.patch,
lucene-1422.patch, lucene-1422.take2.patch, lucene-1422.take3.patch, lucene-1422.take3.patch
>
>
> This is a very early version of the new TokenStream API that 
> we started to discuss here:
> http://www.gossamer-threads.com/lists/lucene/java-dev/66227
> This implementation is a bit different from what I initially
> proposed in the thread above. I introduced a new class called
> AttributedToken, which contains the same termBuffer logic 
> from Token. In addition it has a lazily-initialized map of
> Class<? extends Attribute> -> Attribute. Attribute is also a
> new class in a new package, plus several implementations like
> PositionIncrementAttribute, PayloadAttribute, etc.
> Similar to my initial proposal is the prototypeToken() method
> which the consumer (e. g. DocumentsWriter) needs to call.
> The token is created by the tokenizer at the end of the chain
> and pushed through all filters to the end consumer. The 
> tokenizer and also all filters can add Attributes to the 
> token and can keep references to the actual types of the
> attributes that they need to read of modify. This way, when
> boolean nextToken() is called, no casting is necessary.
> I added a class called TestNewTokenStreamAPI which is not 
> really a test case yet, but has a static demo() method, which
> demonstrates how to use the new API.
> The reason to not merge Token and TokenStream into one class 
> is that we might have caching (or tee/sink) filters in the 
> chain that might want to store cloned copies of the tokens
> in a cache. I added a new class NewCachingTokenStream that
> shows how such a class could work. I also implemented a deep
> clone method in AttributedToken and a 
> copyFrom(AttributedToken) method, which is needed for the 
> caching. Both methods have to iterate over the list of 
> attributes. The Attribute subclasses itself also have a
> copyFrom(Attribute) method, which unfortunately has to down-
> cast to the actual type. I first thought that might be very
> inefficient, but it's not so bad. Well, if you add all
> Attributes to the AttributedToken that our old Token class
> had (like offsets, payload, posIncr), then the performance
> of the caching is somewhat slower (~40%). However, if you 
> add less attributes, because not all might be needed, then
> the performance is even slightly faster than with the old API.
> Also the new API is flexible enough so that someone could
> implement a custom caching filter that knows all attributes
> the token can have, then the caching should be just as 
> fast as with the old API.
> This patch is not nearly ready, there are lot's of things 
> missing:
> - unit tests
> - change DocumentsWriter to use new API 
>   (in backwards-compatible fashion)
> - patch is currently java 1.5; need to change before 
>   commiting to 2.9
> - all TokenStreams and -Filters should be changed to use 
>   new API
> - javadocs incorrect or missing
> - hashcode and equals methods missing in Attributes and 
>   AttributedToken
>   
> I wanted to submit it already for brave people to give me 
> early feedback before I spend more time working on this.

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