Class SynonymGraphFilter

  • All Implemented Interfaces:
    Closeable, AutoCloseable

    public final class SynonymGraphFilter
    extends TokenFilter
    Applies single- or multi-token synonyms from a SynonymMap to an incoming TokenStream, producing a fully correct graph output. This is a replacement for SynonymFilter, which produces incorrect graphs for multi-token synonyms.

    However, if you use this during indexing, you must follow it with FlattenGraphFilter to squash tokens on top of one another like SynonymFilter, because the indexer can't directly consume a graph. To get fully correct positional queries when your synonym replacements are multiple tokens, you should instead apply synonyms using this TokenFilter at query time and translate the resulting graph to a TermAutomatonQuery e.g. using TokenStreamToTermAutomatonQuery.

    NOTE: this cannot consume an incoming graph; results will be undefined.

    • 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
        false for end of stream; true otherwise
      • reset

        public void reset()
                   throws IOException
        Description copied from class: TokenFilter
        This method is called by a consumer before it begins consumption using TokenStream.incrementToken().

        Resets this stream to a clean state. Stateful implementations must implement this method so that they can be reused, just as if they had been created fresh.

        If you override this method, always call super.reset(), otherwise some internal state will not be correctly reset (e.g., Tokenizer will throw IllegalStateException on further usage).

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

        reset in class TokenFilter