Class CollationKeyFilter

  • All Implemented Interfaces:
    Closeable, AutoCloseable

    public final class CollationKeyFilter
    extends TokenFilter
    Use CollationAttributeFactory instead, which encodes terms directly as bytes. This filter will be removed in Lucene 5.0

    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. Since RuleBasedCollators are not independently versioned, it is unsafe to search against stored CollationKeys unless 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. JVM vendor
    2. JVM version, including patch version
    3. The language (and country and variant, if specified) of the Locale used when constructing the collator via Collator.getInstance(java.util.Locale).
    4. The collation strength used - see Collator.setStrength(int)

    The ICUCollationKeyFilter in the analysis-icu package uses ICU4J's Collator, which makes its version available, thus allowing collation to be versioned independently from the JVM. ICUCollationKeyFilter is also 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.

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

    • Constructor Detail

      • CollationKeyFilter

        public CollationKeyFilter​(TokenStream input,
                                  Collator collator)
        input - Source token stream
        collator - CollationKey generator
    • Method Detail

      • incrementToken

        public boolean incrementToken()
                               throws IOException
        Description copied from class: TokenStream
        Consumers (i.e., IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate AttributeImpls with the attributes of the next token.

        The producer must make no assumptions about the attributes after the method has been returned: the caller may arbitrarily change it. If the producer needs to preserve the state for subsequent calls, it can use AttributeSource.captureState() to create a copy of the current attribute state.

        This method is called for every token of a document, so an efficient implementation is crucial for good performance. To avoid calls to AttributeSource.addAttribute(Class) and AttributeSource.getAttribute(Class), references to all AttributeImpls that this stream uses should be retrieved during instantiation.

        To ensure that filters and consumers know which attributes are available, the attributes must be added during instantiation. Filters and consumers are not required to check for availability of attributes in TokenStream.incrementToken().

        Specified by:
        incrementToken in class TokenStream
        false for end of stream; true otherwise