## org.apache.lucene.collation
Class ICUCollationKeyFilter

    java.lang.Object
      org.apache.lucene.util.AttributeSource
          org.apache.lucene.analysis.TokenStream
              org.apache.lucene.analysis.TokenFilter
                  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. `RuleBasedCollator`s 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, 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

### 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`