Package org.apache.lucene.analysis.synonym

Class SynonymGraphFilter

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.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.

    • Constructor Detail

      • SynonymGraphFilter

        public SynonymGraphFilter​(TokenStream input,
                          SynonymMap synonyms,
                          boolean ignoreCase)
        Apply previously built synonyms to incoming tokens.
        Parameters:
        input - input tokenstream
        synonyms - synonym map
        ignoreCase - case-folds input for matching with Character.toLowerCase(int). Note, if you set this to true, it's your responsibility to lowercase the input entries when you create the SynonymMap

    • Method Detail

      • incrementToken

        public boolean incrementToken()
                       throws java.io.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:
        java.io.IOException

      • releaseBufferedToken

        private void releaseBufferedToken()
                           throws java.io.IOException
        Throws:
        java.io.IOException

      • parse

        private boolean parse()
               throws java.io.IOException
        Scans the next input token(s) to see if a synonym matches. Returns true if a match was found.
        Throws:
        java.io.IOException

      • bufferOutputTokens

        private void bufferOutputTokens​(BytesRef bytes,
                                int matchInputLength)
        Expands the output graph into the necessary tokens, adding synonyms as side paths parallel to the input tokens, and buffers them in the output token buffer.

      • capture

        private void capture()
        Buffers the current input token into lookahead buffer.

      • reset

        public void reset()
           throws java.io.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.

        Overrides:
        reset in class TokenFilter
        Throws:
        java.io.IOException

      • getCaptureCount

        int getCaptureCount()

      • getMaxLookaheadUsed

        int getMaxLookaheadUsed()