org.apache.lucene.search.suggest.fst
Class WFSTCompletionLookup

java.lang.Object
  org.apache.lucene.search.suggest.Lookup
      org.apache.lucene.search.suggest.fst.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.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.search.suggest.Lookup

Lookup.LookupPriorityQueue, Lookup.LookupResult

Field Summary

Fields inherited from class org.apache.lucene.search.suggest.Lookup

CHARSEQUENCE_COMPARATOR

Constructor Summary

WFSTCompletionLookup()
Calls WFSTCompletionLookup(true)

WFSTCompletionLookup(boolean exactFirst)
Creates a new suggester.

Method Summary

void	build(TermFreqIterator iterator) Builds up a new internal Lookup representation based on the given TermFreqIterator.
Object	get(CharSequence key) Returns the weight associated with an input string, or null if it does not exist.
boolean	load(InputStream input) Discard current lookup data and load it from a previously saved copy.
List<Lookup.LookupResult>	lookup(CharSequence key, boolean onlyMorePopular, int num) Look up a key and return possible completion for this key.
boolean	store(OutputStream output) Persist the constructed lookup data to a directory.

Methods inherited from class org.apache.lucene.search.suggest.Lookup

build

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

WFSTCompletionLookup

public WFSTCompletionLookup()

Calls WFSTCompletionLookup(true)

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

build

public void build(TermFreqIterator iterator)
           throws IOException

Description copied from class: Lookup

Builds up a new internal Lookup representation based on the given TermFreqIterator. The implementation might re-sort the data internally.

Specified by:

build in class Lookup

Throws:

IOException

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.