Class ICUCollationKeyFilter

  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:

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 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
Constructor Summary
ICUCollationKeyFilter(org.apache.lucene.analysis.TokenStream input, 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, copyTo, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, restoreState, toString
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail


public ICUCollationKeyFilter(org.apache.lucene.analysis.TokenStream input,
input - Source token stream
collator - CollationKey generator
Method Detail


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

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