org.apache.lucene.analysis.query
Class QueryAutoStopWordAnalyzer

java.lang.Object
  org.apache.lucene.analysis.Analyzer
      org.apache.lucene.analysis.AnalyzerWrapper
          org.apache.lucene.analysis.query.QueryAutoStopWordAnalyzer

All Implemented Interfaces:

Closeable

public final class QueryAutoStopWordAnalyzer
extends AnalyzerWrapper

An Analyzer used primarily at query time to wrap another analyzer and provide a layer of protection which prevents very common words from being passed into queries.

For very large indexes the cost of reading TermDocs for a very common word can be high. This analyzer was created after experience with a 38 million doc index which had a term in around 50% of docs and was causing TermQueries for this term to take 2 seconds.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.analysis.Analyzer

Analyzer.GlobalReuseStrategy, Analyzer.PerFieldReuseStrategy, Analyzer.ReuseStrategy, Analyzer.TokenStreamComponents

Field Summary

static float

defaultMaxDocFreqPercent

Constructor Summary

QueryAutoStopWordAnalyzer(Version matchVersion, Analyzer delegate, IndexReader indexReader)
Creates a new QueryAutoStopWordAnalyzer with stopwords calculated for all indexed fields from terms with a document frequency percentage greater than defaultMaxDocFreqPercent

QueryAutoStopWordAnalyzer(Version matchVersion, Analyzer delegate, IndexReader indexReader, Collection<String> fields, float maxPercentDocs)
Creates a new QueryAutoStopWordAnalyzer with stopwords calculated for the given selection of fields from terms with a document frequency percentage greater than the given maxPercentDocs

QueryAutoStopWordAnalyzer(Version matchVersion, Analyzer delegate, IndexReader indexReader, Collection<String> fields, int maxDocFreq)
Creates a new QueryAutoStopWordAnalyzer with stopwords calculated for the given selection of fields from terms with a document frequency greater than the given maxDocFreq

QueryAutoStopWordAnalyzer(Version matchVersion, Analyzer delegate, IndexReader indexReader, float maxPercentDocs)
Creates a new QueryAutoStopWordAnalyzer with stopwords calculated for all indexed fields from terms with a document frequency percentage greater than the given maxPercentDocs

QueryAutoStopWordAnalyzer(Version matchVersion, Analyzer delegate, IndexReader indexReader, int maxDocFreq)
Creates a new QueryAutoStopWordAnalyzer with stopwords calculated for all indexed fields from terms with a document frequency greater than the given maxDocFreq

Method Summary

Term[]	getStopWords() Provides information on which stop words have been identified for all fields
String[]	getStopWords(String fieldName) Provides information on which stop words have been identified for a field
protected Analyzer	getWrappedAnalyzer(String fieldName)
protected Analyzer.TokenStreamComponents	wrapComponents(String fieldName, Analyzer.TokenStreamComponents components)

Methods inherited from class org.apache.lucene.analysis.AnalyzerWrapper

createComponents, getOffsetGap, getPositionIncrementGap, initReader

Methods inherited from class org.apache.lucene.analysis.Analyzer

close, tokenStream

Methods inherited from class java.lang.Object

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

Field Detail

defaultMaxDocFreqPercent

public static final float defaultMaxDocFreqPercent

See Also:

Constant Field Values

Constructor Detail

QueryAutoStopWordAnalyzer

public QueryAutoStopWordAnalyzer(Version matchVersion,
                                 Analyzer delegate,
                                 IndexReader indexReader)
                          throws IOException

Creates a new QueryAutoStopWordAnalyzer with stopwords calculated for all indexed fields from terms with a document frequency percentage greater than defaultMaxDocFreqPercent

Parameters:

matchVersion - Version to be used in StopFilter

delegate - Analyzer whose TokenStream will be filtered

indexReader - IndexReader to identify the stopwords from

Throws:

IOException - Can be thrown while reading from the IndexReader

QueryAutoStopWordAnalyzer

public QueryAutoStopWordAnalyzer(Version matchVersion,
                                 Analyzer delegate,
                                 IndexReader indexReader,
                                 int maxDocFreq)
                          throws IOException

Creates a new QueryAutoStopWordAnalyzer with stopwords calculated for all indexed fields from terms with a document frequency greater than the given maxDocFreq

Parameters:

matchVersion - Version to be used in StopFilter

delegate - Analyzer whose TokenStream will be filtered

indexReader - IndexReader to identify the stopwords from

maxDocFreq - Document frequency terms should be above in order to be stopwords

Throws:

IOException - Can be thrown while reading from the IndexReader

QueryAutoStopWordAnalyzer

public QueryAutoStopWordAnalyzer(Version matchVersion,
                                 Analyzer delegate,
                                 IndexReader indexReader,
                                 float maxPercentDocs)
                          throws IOException

Creates a new QueryAutoStopWordAnalyzer with stopwords calculated for all indexed fields from terms with a document frequency percentage greater than the given maxPercentDocs

Parameters:

matchVersion - Version to be used in StopFilter

delegate - Analyzer whose TokenStream will be filtered

indexReader - IndexReader to identify the stopwords from

maxPercentDocs - The maximum percentage (between 0.0 and 1.0) of index documents which contain a term, after which the word is considered to be a stop word

Throws:

IOException - Can be thrown while reading from the IndexReader

QueryAutoStopWordAnalyzer

public QueryAutoStopWordAnalyzer(Version matchVersion,
                                 Analyzer delegate,
                                 IndexReader indexReader,
                                 Collection<String> fields,
                                 float maxPercentDocs)
                          throws IOException

Creates a new QueryAutoStopWordAnalyzer with stopwords calculated for the given selection of fields from terms with a document frequency percentage greater than the given maxPercentDocs

Parameters:

matchVersion - Version to be used in StopFilter

delegate - Analyzer whose TokenStream will be filtered

indexReader - IndexReader to identify the stopwords from

fields - Selection of fields to calculate stopwords for

maxPercentDocs - The maximum percentage (between 0.0 and 1.0) of index documents which contain a term, after which the word is considered to be a stop word

Throws:

IOException - Can be thrown while reading from the IndexReader

QueryAutoStopWordAnalyzer

public QueryAutoStopWordAnalyzer(Version matchVersion,
                                 Analyzer delegate,
                                 IndexReader indexReader,
                                 Collection<String> fields,
                                 int maxDocFreq)
                          throws IOException

Creates a new QueryAutoStopWordAnalyzer with stopwords calculated for the given selection of fields from terms with a document frequency greater than the given maxDocFreq

Parameters:

matchVersion - Version to be used in StopFilter

delegate - Analyzer whose TokenStream will be filtered

indexReader - IndexReader to identify the stopwords from

fields - Selection of fields to calculate stopwords for

maxDocFreq - Document frequency terms should be above in order to be stopwords

Throws:

IOException - Can be thrown while reading from the IndexReader

Method Detail

getWrappedAnalyzer

protected Analyzer getWrappedAnalyzer(String fieldName)

Specified by:

getWrappedAnalyzer in class AnalyzerWrapper

wrapComponents

protected Analyzer.TokenStreamComponents wrapComponents(String fieldName,
                                                        Analyzer.TokenStreamComponents components)

Specified by:

wrapComponents in class AnalyzerWrapper

getStopWords

public String[] getStopWords(String fieldName)

Provides information on which stop words have been identified for a field

Parameters:

fieldName - The field for which stop words identified in "addStopWords" method calls will be returned

Returns:

the stop words identified for a field

getStopWords

public Term[] getStopWords()

Provides information on which stop words have been identified for all fields

Returns:

the stop words (as terms)