## org.apache.lucene.analysis.query
Class QueryAutoStopWordAnalyzer

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

All Implemented Interfaces:
  Closeable

    public final class QueryAutoStopWordAnalyzer

extends Analyzer

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.

Use the various "addStopWords" methods in this class to automate the identification and addition of stop words found in an already existing index.

Field Summary
`static float` `defaultMaxDocFreqPercent`

Constructor Summary
`QueryAutoStopWordAnalyzer(Version matchVersion, Analyzer delegate)` Initializes this analyzer with the Analyzer object that actually produces the tokens

Method Summary
`int` `addStopWords(IndexReader reader)` Automatically adds stop words for all fields with terms exceeding the defaultMaxDocFreqPercent
`int` `addStopWords(IndexReader reader, float maxPercentDocs)` Automatically adds stop words for all fields with terms exceeding the maxDocFreqPercent
`int` `addStopWords(IndexReader reader, int maxDocFreq)` Automatically adds stop words for all fields with terms exceeding the maxDocFreqPercent
`int` `addStopWords(IndexReader reader, String fieldName, float maxPercentDocs)` Automatically adds stop words for the given field with terms exceeding the maxPercentDocs
`int` `addStopWords(IndexReader reader, String fieldName, int maxDocFreq)` Automatically adds stop words for the given field with terms exceeding the maxPercentDocs
`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
`TokenStream` `reusableTokenStream(String fieldName, Reader reader)` Creates a TokenStream that is allowed to be re-used from the previous time that the same thread called this method.
`TokenStream` `tokenStream(String fieldName, Reader reader)` Creates a TokenStream which tokenizes all the text in the provided Reader.

Methods inherited from class org.apache.lucene.analysis.Analyzer
`close, getOffsetGap, getPositionIncrementGap, getPreviousTokenStream, setPreviousTokenStream`

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)

  Initializes this analyzer with the Analyzer object that actually produces the tokens

  Parameters:
    `delegate` - The choice of `Analyzer` that is used to produce the token stream which needs filtering

Method Detail

### addStopWords

    public int addStopWords(IndexReader reader)
                     throws IOException

  Automatically adds stop words for all fields with terms exceeding the defaultMaxDocFreqPercent

  Parameters:
    `reader` - The `IndexReader` which will be consulted to identify potential stop words that exceed the required document frequency
  Returns:
    The number of stop words identified.
  Throws:
    `IOException`

### addStopWords

    public int addStopWords(IndexReader reader,
                            int maxDocFreq)
                     throws IOException

  Automatically adds stop words for all fields with terms exceeding the maxDocFreqPercent

  Parameters:
    `reader` - The `IndexReader` which will be consulted to identify potential stop words that exceed the required document frequency
    `maxDocFreq` - The maximum number of index documents which can contain a term, after which the term is considered to be a stop word
  Returns:
    The number of stop words identified.
  Throws:
    `IOException`

### addStopWords

    public int addStopWords(IndexReader reader,
                            float maxPercentDocs)
                     throws IOException

  Automatically adds stop words for all fields with terms exceeding the maxDocFreqPercent

  Parameters:
    `reader` - The `IndexReader` which will be consulted to identify potential stop words that exceed the required document frequency
    `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.
  Returns:
    The number of stop words identified.
  Throws:
    `IOException`

### addStopWords

    public int addStopWords(IndexReader reader,
                            String fieldName,
                            float maxPercentDocs)
                     throws IOException

  Automatically adds stop words for the given field with terms exceeding the maxPercentDocs

  Parameters:
    `reader` - The `IndexReader` which will be consulted to identify potential stop words that exceed the required document frequency
    `fieldName` - The field for which stopwords will be added
    `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.
  Returns:
    The number of stop words identified.
  Throws:
    `IOException`

### addStopWords

    public int addStopWords(IndexReader reader,
                            String fieldName,
                            int maxDocFreq)
                     throws IOException

  Automatically adds stop words for the given field with terms exceeding the maxPercentDocs

  Parameters:
    `reader` - The `IndexReader` which will be consulted to identify potential stop words that exceed the required document frequency
    `fieldName` - The field for which stopwords will be added
    `maxDocFreq` - The maximum number of index documents which can contain a term, after which the term is considered to be a stop word.
  Returns:
    The number of stop words identified.
  Throws:
    `IOException`

### tokenStream

    public TokenStream tokenStream(String fieldName,
                                   Reader reader)

  Description copied from class: `Analyzer`
  Creates a TokenStream which tokenizes all the text in the provided Reader. Must be able to handle null field name for backward compatibility.

  Specified by:
    `tokenStream` in class `Analyzer`

### reusableTokenStream

    public TokenStream reusableTokenStream(String fieldName,
                                           Reader reader)
                                    throws IOException

  Description copied from class: `Analyzer`
  Creates a TokenStream that is allowed to be re-used from the previous time that the same thread called this method. Callers that do not need to use more than one TokenStream at the same time from this analyzer should use this method for better performance.

  Overrides:
    `reusableTokenStream` in class `Analyzer`
  Throws:
    `IOException`

### 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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