Package org.apache.lucene.search.suggest.fst

Class WFSTCompletionLookup

  • public class WFSTCompletionLookup
extends Lookup
    Suggester based on a weighted FST: it first traverses the prefix, then walks the n shortest paths to retrieve top-ranked suggestions.

    NOTE: Although the TermFreqIterator API specifies floating point weights, input weights should be whole numbers. Input weights will be cast to a java integer, and any negative, infinite, or NaN values will be rejected.

    See Also:
    Util.shortestPaths(FST, FST.Arc, Comparator, int)
    WARNING: This API is experimental and might change in incompatible ways in the next release.

    • Constructor Detail

      • WFSTCompletionLookup

        public WFSTCompletionLookup​(boolean exactFirst)
        Creates a new suggester.
        Parameters:
        exactFirst - true if suggestions that match the prefix exactly should always be returned first, regardless of score. This has no performance impact, but could result in low-quality suggestions.

    • Method Detail

      • store

        public boolean store​(OutputStream output)
              throws IOException
        Description copied from class: Lookup
        Persist the constructed lookup data to a directory. Optional operation.
        Specified by:
        store in class Lookup
        Parameters:
        output - OutputStream to write the data to.
        Returns:
        true if successful, false if unsuccessful or not supported.
        Throws:
        IOException - when fatal IO error occurs.

      • load

        public boolean load​(InputStream input)
             throws IOException
        Description copied from class: Lookup
        Discard current lookup data and load it from a previously saved copy. Optional operation.
        Specified by:
        load in class Lookup
        Parameters:
        input - the InputStream to load the lookup data.
        Returns:
        true if completed successfully, false if unsuccessful or not supported.
        Throws:
        IOException - when fatal IO error occurs.

      • lookup

        public List<Lookup.LookupResult> lookup​(CharSequence key,
                                        boolean onlyMorePopular,
                                        int num)
        Description copied from class: Lookup
        Look up a key and return possible completion for this key.
        Specified by:
        lookup in class Lookup
        Parameters:
        key - lookup key. Depending on the implementation this may be a prefix, misspelling, or even infix.
        onlyMorePopular - return only more popular results
        num - maximum number of results to return
        Returns:
        a list of possible completions, with their relative weight (e.g. popularity)

      • get

        public Object get​(CharSequence key)
        Returns the weight associated with an input string, or null if it does not exist.