Class SynonymFilter

  • All Implemented Interfaces:
    Closeable, AutoCloseable

    public final class SynonymFilter
    extends org.apache.lucene.analysis.TokenFilter
    Matches single or multi word synonyms in a token stream. This token stream cannot properly handle position increments != 1, ie, you should place this filter before filtering out stop words.

    Note that with the current implementation, parsing is greedy, so whenever multiple parses would apply, the rule starting the earliest and parsing the most tokens wins. For example if you have these rules:

       a -> x
       a b -> y
       b c d -> z
     
    Then input a b c d e parses to y b c d, ie the 2nd rule "wins" because it started earliest and matched the most input tokens of other rules starting at that point.

    A future improvement to this filter could allow non-greedy parsing, such that the 3rd rule would win, and also separately allow multiple parses, such that all 3 rules would match, perhaps even on a rule by rule basis.

    NOTE: when a match occurs, the output tokens associated with the matching rule are "stacked" on top of the input stream (if the rule had keepOrig=true) and also on top of aother matched rule's output tokens. This is not a correct solution, as really the output should be an abitrary graph/lattice. For example, with the above match, you would expect an exact PhraseQuery "y b c" to match the parsed tokens, but it will fail to do so. This limitations is necessary because Lucene's TokenStream (and index) cannot yet represent an arbitrary graph.

    NOTE: If multiple incoming tokens arrive on the same position, only the first token at that position is used for parsing. Subsequent tokens simply pass through and are not parsed. A future improvement would be to allow these tokens to also be matched.

    • Nested Class Summary

      • Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource

        org.apache.lucene.util.AttributeSource.AttributeFactory, org.apache.lucene.util.AttributeSource.State
    • Field Summary

      Fields 
      Modifier and Type Field Description
      static String TYPE_SYNONYM  
      • Fields inherited from class org.apache.lucene.analysis.TokenFilter

        input
    • Constructor Summary

      Constructors 
      Constructor Description
      SynonymFilter​(org.apache.lucene.analysis.TokenStream input, SynonymMap synonyms, boolean ignoreCase)  
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      boolean incrementToken()  
      void reset()  
      • Methods inherited from class org.apache.lucene.analysis.TokenFilter

        close, end
      • Methods inherited from class org.apache.lucene.util.AttributeSource

        addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, restoreState, toString
    • Constructor Detail

      • SynonymFilter

        public SynonymFilter​(org.apache.lucene.analysis.TokenStream input,
                             SynonymMap synonyms,
                             boolean ignoreCase)
        Parameters:
        input - input tokenstream
        synonyms - synonym map
        ignoreCase - case-folds input for matching with Character.toLowerCase(int). Note, if you set this to true, its your responsibility to lowercase the input entries when you create the SynonymMap
    • Method Detail

      • incrementToken

        public boolean incrementToken()
                               throws IOException
        Specified by:
        incrementToken in class org.apache.lucene.analysis.TokenStream
        Throws:
        IOException
      • reset

        public void reset()
                   throws IOException
        Overrides:
        reset in class org.apache.lucene.analysis.TokenFilter
        Throws:
        IOException