org.apache.lucene.search.spell
Class SpellChecker

java.lang.Object
  extended by org.apache.lucene.search.spell.SpellChecker
All Implemented Interfaces:
Closeable

public class SpellChecker
extends Object
implements Closeable

Spell Checker class (Main class)
(initially inspired by the David Spencer code).

Example Usage:

  SpellChecker spellchecker = new SpellChecker(spellIndexDirectory);
  // To index a field of a user index:
  spellchecker.indexDictionary(new LuceneDictionary(my_lucene_reader, a_field));
  // To index a file containing words:
  spellchecker.indexDictionary(new PlainTextDictionary(new File("myfile.txt")));
  String[] suggestions = spellchecker.suggestSimilar("misspelt", 5);
 

Version:
1.0

Field Summary
static String F_WORD
          Field name for each word in the ngram index.
 
Constructor Summary
SpellChecker(org.apache.lucene.store.Directory spellIndex)
          Use the given directory as a spell checker index with a LevensteinDistance as the default StringDistance.
SpellChecker(org.apache.lucene.store.Directory spellIndex, StringDistance sd)
          Use the given directory as a spell checker index.
 
Method Summary
 void clearIndex()
          Removes all terms from the spell check index.
 void close()
          Close the IndexSearcher used by this SpellChecker
 boolean exist(String word)
          Check whether the word exists in the index.
 StringDistance getStringDistance()
          Returns the StringDistance instance used by this SpellChecker instance.
 void indexDictionary(Dictionary dict)
          Indexes the data from the given Dictionary.
 void indexDictionary(Dictionary dict, int mergeFactor, int ramMB)
          Indexes the data from the given Dictionary.
 void setAccuracy(float minScore)
          Sets the accuracy 0 < minScore < 1; default 0.5
 void setSpellIndex(org.apache.lucene.store.Directory spellIndexDir)
          Use a different index as the spell checker index or re-open the existing index if spellIndex is the same value as given in the constructor.
 void setStringDistance(StringDistance sd)
          Sets the StringDistance implementation for this SpellChecker instance.
 String[] suggestSimilar(String word, int numSug)
          Suggest similar words.
 String[] suggestSimilar(String word, int numSug, org.apache.lucene.index.IndexReader ir, String field, boolean morePopular)
          Suggest similar words (optionally restricted to a field of an index).
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

F_WORD

public static final String F_WORD
Field name for each word in the ngram index.

See Also:
Constant Field Values
Constructor Detail

SpellChecker

public SpellChecker(org.apache.lucene.store.Directory spellIndex,
                    StringDistance sd)
             throws IOException
Use the given directory as a spell checker index. The directory is created if it doesn't exist yet.

Parameters:
spellIndex - the spell index directory
sd - the StringDistance measurement to use
Throws:
IOException - if Spellchecker can not open the directory

SpellChecker

public SpellChecker(org.apache.lucene.store.Directory spellIndex)
             throws IOException
Use the given directory as a spell checker index with a LevensteinDistance as the default StringDistance. The directory is created if it doesn't exist yet.

Parameters:
spellIndex - the spell index directory
Throws:
IOException - if spellchecker can not open the directory
Method Detail

setSpellIndex

public void setSpellIndex(org.apache.lucene.store.Directory spellIndexDir)
                   throws IOException
Use a different index as the spell checker index or re-open the existing index if spellIndex is the same value as given in the constructor.

Parameters:
spellIndexDir - the spell directory to use
Throws:
org.apache.lucene.store.AlreadyClosedException - if the Spellchecker is already closed
IOException - if spellchecker can not open the directory

setStringDistance

public void setStringDistance(StringDistance sd)
Sets the StringDistance implementation for this SpellChecker instance.

Parameters:
sd - the StringDistance implementation for this SpellChecker instance

getStringDistance

public StringDistance getStringDistance()
Returns the StringDistance instance used by this SpellChecker instance.

Returns:
the StringDistance instance used by this SpellChecker instance.

setAccuracy

public void setAccuracy(float minScore)
Sets the accuracy 0 < minScore < 1; default 0.5


suggestSimilar

public String[] suggestSimilar(String word,
                               int numSug)
                        throws IOException
Suggest similar words.

As the Lucene similarity that is used to fetch the most relevant n-grammed terms is not the same as the edit distance strategy used to calculate the best matching spell-checked word from the hits that Lucene found, one usually has to retrieve a couple of numSug's in order to get the true best match.

I.e. if numSug == 1, don't count on that suggestion being the best one. Thus, you should set this value to at least 5 for a good suggestion.

Parameters:
word - the word you want a spell check done on
numSug - the number of suggested words
Returns:
String[]
Throws:
IOException - if the underlying index throws an IOException
org.apache.lucene.store.AlreadyClosedException - if the Spellchecker is already closed

suggestSimilar

public String[] suggestSimilar(String word,
                               int numSug,
                               org.apache.lucene.index.IndexReader ir,
                               String field,
                               boolean morePopular)
                        throws IOException
Suggest similar words (optionally restricted to a field of an index).

As the Lucene similarity that is used to fetch the most relevant n-grammed terms is not the same as the edit distance strategy used to calculate the best matching spell-checked word from the hits that Lucene found, one usually has to retrieve a couple of numSug's in order to get the true best match.

I.e. if numSug == 1, don't count on that suggestion being the best one. Thus, you should set this value to at least 5 for a good suggestion.

Parameters:
word - the word you want a spell check done on
numSug - the number of suggested words
ir - the indexReader of the user index (can be null see field param)
field - the field of the user index: if field is not null, the suggested words are restricted to the words present in this field.
morePopular - return only the suggest words that are as frequent or more frequent than the searched word (only if restricted mode = (indexReader!=null and field!=null)
Returns:
String[] the sorted list of the suggest words with these 2 criteria: first criteria: the edit distance, second criteria (only if restricted mode): the popularity of the suggest words in the field of the user index
Throws:
IOException - if the underlying index throws an IOException
org.apache.lucene.store.AlreadyClosedException - if the Spellchecker is already closed

clearIndex

public void clearIndex()
                throws IOException
Removes all terms from the spell check index.

Throws:
IOException
org.apache.lucene.store.AlreadyClosedException - if the Spellchecker is already closed

exist

public boolean exist(String word)
              throws IOException
Check whether the word exists in the index.

Parameters:
word -
Returns:
true if the word exists in the index
Throws:
IOException
org.apache.lucene.store.AlreadyClosedException - if the Spellchecker is already closed

indexDictionary

public void indexDictionary(Dictionary dict,
                            int mergeFactor,
                            int ramMB)
                     throws IOException
Indexes the data from the given Dictionary.

Parameters:
dict - Dictionary to index
mergeFactor - mergeFactor to use when indexing
ramMB - the max amount or memory in MB to use
Throws:
org.apache.lucene.store.AlreadyClosedException - if the Spellchecker is already closed
IOException

indexDictionary

public void indexDictionary(Dictionary dict)
                     throws IOException
Indexes the data from the given Dictionary.

Parameters:
dict - the dictionary to index
Throws:
IOException

close

public void close()
           throws IOException
Close the IndexSearcher used by this SpellChecker

Specified by:
close in interface Closeable
Throws:
IOException - if the close operation causes an IOException
org.apache.lucene.store.AlreadyClosedException - if the SpellChecker is already closed


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