## org.apache.lucene.analysis.miscellaneous
Class PatternAnalyzer

    java.lang.Object
      org.apache.lucene.analysis.Analyzer
          org.apache.lucene.analysis.ReusableAnalyzerBase
              org.apache.lucene.analysis.miscellaneous.PatternAnalyzer

All Implemented Interfaces:
  Closeable

    public final class PatternAnalyzer

extends org.apache.lucene.analysis.ReusableAnalyzerBase

Efficient Lucene analyzer/tokenizer that preferably operates on a String rather than a `Reader`, that can flexibly separate text into terms via a regular expression `Pattern` (with behaviour identical to `String.split(String)`), and that combines the functionality of `LetterTokenizer`, `LowerCaseTokenizer`, `WhitespaceTokenizer`, `StopFilter` into a single efficient multi-purpose class.

If you are unsure how exactly a regular expression should look like, consider prototyping by simply trying various expressions on some test texts via `String.split(String)`. Once you are satisfied, give that regex to PatternAnalyzer. Also see Java Regular Expression Tutorial.

This class can be considerably faster than the "normal" Lucene tokenizers. It can also serve as a building block in a compound Lucene `TokenFilter` chain. For example as in this stemming example:

     PatternAnalyzer pat = ...
     TokenStream tokenStream = new SnowballFilter(
         pat.tokenStream("content", "James is running round in the woods"),
         "English"));

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.analysis.ReusableAnalyzerBase
`org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents`

Field Summary
`static PatternAnalyzer` `DEFAULT_ANALYZER` A lower-casing word analyzer with English stop words (can be shared freely across threads without harm); global per class loader.
`static PatternAnalyzer` `EXTENDED_ANALYZER` A lower-casing word analyzer with extended English stop words (can be shared freely across threads without harm); global per class loader.
`static Pattern` `NON_WORD_PATTERN` `"\\W+"`; Divides text at non-letters (NOT Character.isLetter(c))
`static Pattern` `WHITESPACE_PATTERN` `"\\s+"`; Divides text at whitespaces (Character.isWhitespace(c))

Constructor Summary
`PatternAnalyzer(org.apache.lucene.util.Version matchVersion, Pattern pattern, boolean toLowerCase, Set<?> stopWords)` Constructs a new instance with the given parameters.

Method Summary
`org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents` `createComponents(String fieldName, Reader reader)` Creates a token stream that tokenizes all the text in the given Reader; This implementation forwards to `tokenStream(String, Reader, String)` and is less efficient than `tokenStream(String, Reader, String)`.
`org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents` `createComponents(String fieldName, Reader reader, String text)` Creates a token stream that tokenizes the given string into token terms (aka words).
`boolean` `equals(Object other)` Indicates whether some other object is "equal to" this one.
`int` `hashCode()` Returns a hash code value for the object.

Methods inherited from class org.apache.lucene.analysis.ReusableAnalyzerBase
`initReader, reusableTokenStream, tokenStream`

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

Methods inherited from class java.lang.Object
`clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### NON_WORD_PATTERN

    public static final Pattern NON_WORD_PATTERN

  `"\\W+"`; Divides text at non-letters (NOT Character.isLetter(c))

### WHITESPACE_PATTERN

    public static final Pattern WHITESPACE_PATTERN

  `"\\s+"`; Divides text at whitespaces (Character.isWhitespace(c))

### DEFAULT_ANALYZER

    public static final PatternAnalyzer DEFAULT_ANALYZER

  A lower-casing word analyzer with English stop words (can be shared freely across threads without harm); global per class loader.

### EXTENDED_ANALYZER

    public static final PatternAnalyzer EXTENDED_ANALYZER

  A lower-casing word analyzer with extended English stop words (can be shared freely across threads without harm); global per class loader. The stop words are borrowed from http://thomas.loc.gov/home/stopwords.html, see http://thomas.loc.gov/home/all.about.inquery.html

Constructor Detail

### PatternAnalyzer

    public PatternAnalyzer(org.apache.lucene.util.Version matchVersion,
                           Pattern pattern,
                           boolean toLowerCase,
                           Set<?> stopWords)

  Constructs a new instance with the given parameters.

  Parameters:
    `matchVersion` - currently does nothing
    `pattern` - a regular expression delimiting tokens
    `toLowerCase` - if `true` returns tokens after applying String.toLowerCase()
    `stopWords` - if non-null, ignores all tokens that are contained in the given stop set (after previously having applied toLowerCase() if applicable). For example, created via `StopFilter.makeStopSet(Version, String[])`and/or `WordlistLoader`as in `WordlistLoader.getWordSet(new File("samples/fulltext/stopwords.txt")` or other stop words lists .

Method Detail

### createComponents

    public org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents createComponents(String fieldName,
                                                                                                  Reader reader,
                                                                                                  String text)

  Creates a token stream that tokenizes the given string into token terms (aka words).

  Parameters:
    `fieldName` - the name of the field to tokenize (currently ignored).
    `reader` - reader (e.g. charfilter) of the original text. can be null.
    `text` - the string to tokenize
  Returns:
    a new token stream

### createComponents

    public org.apache.lucene.analysis.ReusableAnalyzerBase.TokenStreamComponents createComponents(String fieldName,
                                                                                                  Reader reader)

  Creates a token stream that tokenizes all the text in the given Reader; This implementation forwards to `tokenStream(String, Reader, String)` and is less efficient than `tokenStream(String, Reader, String)`.

  Specified by:
    `createComponents` in class `org.apache.lucene.analysis.ReusableAnalyzerBase`
  Parameters:
    `fieldName` - the name of the field to tokenize (currently ignored).
    `reader` - the reader delivering the text
  Returns:
    a new token stream

### equals

    public boolean equals(Object other)

  Indicates whether some other object is "equal to" this one.

  Overrides:
    `equals` in class `Object`
  Parameters:
    `other` - the reference object with which to compare.
  Returns:
    true if equal, false otherwise

### hashCode

    public int hashCode()

  Returns a hash code value for the object.

  Overrides:
    `hashCode` in class `Object`
  Returns:
    the hash code.