Class TokenStream

    • Constructor Detail

      • TokenStream

        protected TokenStream()
        A TokenStream using the default attribute factory.
      • TokenStream

        protected TokenStream​(AttributeSource input)
        A TokenStream that uses the same attributes as the supplied one.
    • Method Detail

      • incrementToken

        public abstract boolean incrementToken()
                                        throws IOException
        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 incrementToken().

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

        public void end()
                 throws IOException
        This method is called by the consumer after the last token has been consumed, after 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.

        Throws:
        IOException
      • reset

        public void reset()
                   throws IOException
        Resets this stream to the beginning. This is an optional operation, so subclasses may or may not implement this method. reset() is not needed for the standard indexing process. However, if the tokens of a TokenStream are intended to be consumed more than once, it is necessary to implement reset(). Note that if your TokenStream caches tokens and feeds them back again after a reset, it is imperative that you clone the tokens when you store them away (on the first pass) as well as when you return them (on future passes after reset()).
        Throws:
        IOException