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, AutoCloseable

      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.ReuseStrategy, Analyzer.TokenStreamComponents`

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static float` | `defaultMaxDocFreqPercent`

    - ### Fields inherited from class org.apache.lucene.analysis.Analyzer

      `GLOBAL_REUSE_STRATEGY, PER_FIELD_REUSE_STRATEGY`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `QueryAutoStopWordAnalyzer(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(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(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(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(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

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `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, wrapReader`

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

      `close, getReuseStrategy, getVersion, setVersion, tokenStream, 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(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:
        `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(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:
        `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(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:
        `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(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:
        `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(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:
        `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)

      Overrides:
        `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)

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