org.apache.lucene.collation
Class ICUCollationKeyFilter

java.lang.Object
  extended by org.apache.lucene.util.AttributeSource
      extended by org.apache.lucene.analysis.TokenStream
          extended by org.apache.lucene.analysis.TokenFilter
              extended by org.apache.lucene.collation.ICUCollationKeyFilter
All Implemented Interfaces:
Closeable

public final class ICUCollationKeyFilter
extends org.apache.lucene.analysis.TokenFilter

Converts each token into its CollationKey, and then encodes the CollationKey with IndexableBinaryStringTools, to allow it to be stored as an index term.

WARNING: Make sure you use exactly the same Collator at index and query time -- CollationKeys are only comparable when produced by the same Collator. RuleBasedCollators are independently versioned, so it is safe to search against stored CollationKeys if the following are exactly the same (best practice is to store this information with the index and check that they remain the same at query time):

  1. Collator version - see Collator.getVersion()
  2. The collation strength used - see Collator.setStrength(int)

CollationKeys generated by ICU Collators are not compatible with those generated by java.text.Collators. Specifically, if you use ICUCollationKeyFilter to generate index terms, do not use CollationKeyFilter on the query side, or vice versa.

ICUCollationKeyFilter is significantly faster and generates significantly shorter keys than CollationKeyFilter. See http://site.icu-project.org/charts/collation-icu4j-sun for key generation timing and key length comparisons between ICU4J and java.text.Collator over several languages.


Nested Class Summary
 
Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource
org.apache.lucene.util.AttributeSource.AttributeFactory, org.apache.lucene.util.AttributeSource.State
 
Field Summary
 
Fields inherited from class org.apache.lucene.analysis.TokenFilter
input
 
Constructor Summary
ICUCollationKeyFilter(org.apache.lucene.analysis.TokenStream input, com.ibm.icu.text.Collator collator)
           
 
Method Summary
 boolean incrementToken()
           
 
Methods inherited from class org.apache.lucene.analysis.TokenFilter
close, end, reset
 
Methods inherited from class org.apache.lucene.util.AttributeSource
addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, restoreState, toString
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

ICUCollationKeyFilter

public ICUCollationKeyFilter(org.apache.lucene.analysis.TokenStream input,
                             com.ibm.icu.text.Collator collator)
Parameters:
input - Source token stream
collator - CollationKey generator
Method Detail

incrementToken

public boolean incrementToken()
                       throws IOException
Specified by:
incrementToken in class org.apache.lucene.analysis.TokenStream
Throws:
IOException


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