org.apache.lucene.analysis.cjk

Class CJKWidthFilter

  • All Implemented Interfaces:
    Closeable, AutoCloseable


    public final class CJKWidthFilter
    extends TokenFilter
    A TokenFilter that normalizes CJK width differences:
    • Folds fullwidth ASCII variants into the equivalent basic latin
    • Folds halfwidth Katakana variants into the equivalent kana

    NOTE: this filter can be viewed as a (practical) subset of NFKC/NFKD Unicode normalization. See the normalization support in the ICU package for full normalization.

    • 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
        Returns:
        false for end of stream; true otherwise
        Throws:
        IOException