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

Class WFSTCompletionLookup

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

    NOTE: Input weights must be between 0 and Integer.MAX_VALUE, any other values will be rejected.

    • Field Detail

      • fst

        private FST<java.lang.Long> fst
        FST, weights are encoded as costs: (Integer.MAX_VALUE-weight)

      • exactFirst

        private final boolean exactFirst
        True if exact match suggestions should always be returned first.

      • count

        private long count
        Number of entries the lookup was built with

      • tempFileNamePrefix

        private final java.lang.String tempFileNamePrefix

      • weightComparator

        static final java.util.Comparator<java.lang.Long> weightComparator

    • Constructor Detail

      • WFSTCompletionLookup

        public WFSTCompletionLookup​(Directory tempDir,
                            java.lang.String tempFileNamePrefix,
                            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

      • build

        public void build​(InputIterator iterator)
           throws java.io.IOException
        Description copied from class: Lookup
        Builds up a new internal Lookup representation based on the given InputIterator. The implementation might re-sort the data internally.
        Specified by:
        build in class Lookup
        Throws:
        java.io.IOException

      • store

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

      • load

        public boolean load​(DataInput input)
             throws java.io.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 DataInput to load the lookup data.
        Returns:
        true if completed successfully, false if unsuccessful or not supported.
        Throws:
        java.io.IOException - when fatal IO error occurs.

      • lookup

        public java.util.List<Lookup.LookupResult> lookup​(java.lang.CharSequence key,
                                                  java.util.Set<BytesRef> contexts,
                                                  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.
        contexts - contexts to filter the lookup by, or null if all contexts are allowed; if the suggestion contains any of the contexts, it's a match
        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)

      • lookupPrefix

        private java.lang.Long lookupPrefix​(BytesRef scratch,
                                    FST.Arc<java.lang.Long> arc)
                             throws java.io.IOException
        Throws:
        java.io.IOException

      • get

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

      • decodeWeight

        private static int decodeWeight​(long encoded)
        cost -> weight

      • encodeWeight

        private static int encodeWeight​(long value)
        weight -> cost

      • ramBytesUsed

        public long ramBytesUsed()
        Returns byte size of the underlying FST.
        Specified by:
        ramBytesUsed in interface Accountable

      • getChildResources

        public java.util.Collection<Accountable> getChildResources()
        Description copied from interface: Accountable
        Returns nested resources of this class. The result should be a point-in-time snapshot (to avoid race conditions).
        Specified by:
        getChildResources in interface Accountable
        See Also:
        Accountables

      • getCount

        public long getCount()
        Description copied from class: Lookup
        Get the number of entries the lookup was built with
        Specified by:
        getCount in class Lookup
        Returns:
        total number of suggester entries