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More AttributeSource usage tips. addAttribute/getAttribute leads often to a misunderstanding (even the core developers) :-) 

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@807831 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Uwe Schindler 2009-08-25 22:09:46 +00:00
parent cd1fd9768f
commit 40b90c98c4
1 changed files with 15 additions and 4 deletions
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19
src/java/org/apache/lucene/analysis/package.html
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@ -327,7 +327,11 @@ All methods in AttributeSource are idempotent, which means calling them multiple
result. This is especially important to know for addAttribute(). The method takes the <b>type</b> (<code>Class</code>)
of an Attribute as an argument and returns an <b>instance</b>. If an Attribute of the same type was previously added, then
the already existing instance is returned, otherwise a new instance is created and returned. Therefore TokenStreams/-Filters
can safely call addAttribute() with the same Attribute type multiple times.
can safely call addAttribute() with the same Attribute type multiple times. Even consumers of TokenStreams should
normally call addAttribute() instead of getAttribute(), because it would not fail if the TokenStream does not have this
Attribute (getAttribute() would throw an IllegalArgumentException, if the Attribute is missing). More advanced code
could simply check with hasAttribute(), if a TokenStream has it, and may conditionally leave out processing for
extra performance.
</li></ol>
<h3>Example</h3>
In this example we will create a WhiteSpaceTokenizer and use a LengthFilter to suppress all words that only
@ -352,7 +356,9 @@ public class MyAnalyzer extends Analyzer {
TokenStream stream = analyzer.tokenStream("field", new StringReader(text));
// get the TermAttribute from the TokenStream
TermAttribute termAtt = (TermAttribute) stream.getAttribute(TermAttribute.class);
TermAttribute termAtt = (TermAttribute) stream.addAttribute(TermAttribute.class);
stream.reset();
// print all tokens until stream is exhausted
while (stream.incrementToken()) {
@ -573,15 +579,20 @@ to make use of the new PartOfSpeechAttribute and print it out:
TokenStream stream = analyzer.tokenStream("field", new StringReader(text));
// get the TermAttribute from the TokenStream
TermAttribute termAtt = (TermAttribute) stream.getAttribute(TermAttribute.class);
TermAttribute termAtt = (TermAttribute) stream.addAttribute(TermAttribute.class);
// get the PartOfSpeechAttribute from the TokenStream
PartOfSpeechAttribute posAtt = (PartOfSpeechAttribute) stream.getAttribute(PartOfSpeechAttribute.class);
PartOfSpeechAttribute posAtt = (PartOfSpeechAttribute) stream.addAttribute(PartOfSpeechAttribute.class);
stream.reset();
// print all tokens until stream is exhausted
while (stream.incrementToken()) {
System.out.println(termAtt.term() + ": " + posAtt.getPartOfSpeech());
}
stream.end();
stream.close();
}
</pre>
The change that was made is to get the PartOfSpeechAttribute from the TokenStream and print out its contents in