Class ICUNormalizer2Filter

  • All Implemented Interfaces:
    Closeable, AutoCloseable
    Direct Known Subclasses:

    public class ICUNormalizer2Filter
    extends TokenFilter
    Normalize token text with ICU's

    With this filter, you can normalize text in the following ways:

    • NFKC Normalization, Case Folding, and removing Ignorables (the default)
    • Using a standard Normalization mode (NFC, NFD, NFKC, NFKD)
    • Based on rules from a custom normalization mapping.

    If you use the defaults, this filter is a simple way to standardize Unicode text in a language-independent way for search:

    • The case folding that it does can be seen as a replacement for LowerCaseFilter: For example, it handles cases such as the Greek sigma, so that "Μάϊος" and "ΜΆΪΟΣ" will match correctly.
    • The normalization will standardizes different forms of the same character in Unicode. For example, CJK full-width numbers will be standardized to their ASCII forms.
    • Ignorables such as Zero-Width Joiner and Variation Selectors are removed. These are typically modifier characters that affect display.
    See Also:,
    • Constructor Detail

      • ICUNormalizer2Filter

        public ICUNormalizer2Filter(TokenStream input)
        Create a new Normalizer2Filter that combines NFKC normalization, Case Folding, and removes Default Ignorables (NFKC_Casefold)
      • ICUNormalizer2Filter

        public ICUNormalizer2Filter(TokenStream input,
                                    Normalizer2 normalizer)
        Create a new Normalizer2Filter with the specified Normalizer2
        input - stream
        normalizer - normalizer to use
    • Method Detail

      • incrementToken

        public final 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