Class GermanNormalizationFilter

  • All Implemented Interfaces:, java.lang.AutoCloseable

    public final class GermanNormalizationFilter
    extends TokenFilter
    Normalizes German characters according to the heuristics of the German2 snowball algorithm. It allows for the fact that ä, ö and ü are sometimes written as ae, oe and ue.

    • 'ß' is replaced by 'ss'
    • 'ä', 'ö', 'ü' are replaced by 'a', 'o', 'u', respectively.
    • 'ae' and 'oe' are replaced by 'a', and 'o', respectively.
    • 'ue' is replaced by 'u', when not following a vowel or q.

    This is useful if you want this normalization without using the German2 stemmer, or perhaps no stemming at all.

    • Constructor Detail

      • GermanNormalizationFilter

        public GermanNormalizationFilter​(TokenStream input)
    • Method Detail

      • incrementToken

        public boolean incrementToken()
        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