Class CachingTokenFilter

  • All Implemented Interfaces:
    Closeable, AutoCloseable

    public final class CachingTokenFilter
    extends TokenFilter
    This class can be used if the token attributes of a TokenStream are intended to be consumed more than once. It caches all token attribute states locally in a List.

    CachingTokenFilter implements the optional method TokenStream.reset(), which repositions the stream to the first Token.

    • Constructor Detail

      • CachingTokenFilter

        public CachingTokenFilter​(TokenStream input)
        Create a new CachingTokenFilter around input, caching its token attributes, which can be replayed again after a call to reset().
    • 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
      • end

        public final void end()
        Description copied from class: TokenFilter
        This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new TokenStream API). Streams implementing the old API should upgrade to use this feature.

        This method can be used to perform any end-of-stream operations, such as setting the final offset of a stream. The final offset of a stream might differ from the offset of the last token eg in case one or more whitespaces followed after the last token, but a WhitespaceTokenizer was used.

        Additionally any skipped positions (such as those removed by a stopfilter) can be applied to the position increment, or any adjustment of other attributes where the end-of-stream value may be important.

        If you override this method, always call super.end().

        NOTE: The default implementation chains the call to the input TokenStream, so be sure to call super.end() first when overriding this method.

        end in class TokenFilter
      • reset

        public void reset()
        Rewinds the iterator to the beginning of the cached list.

        Note that this does not call reset() on the wrapped tokenstream ever, even the first time. You should reset() the inner tokenstream before wrapping it with CachingTokenFilter.

        reset in class TokenFilter