org.apache.lucene.index.memory
Class PatternAnalyzer

java.lang.Object
  org.apache.lucene.analysis.Analyzer
      org.apache.lucene.index.memory.PatternAnalyzer

public class PatternAnalyzer
extends Analyzer

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"));
 

Author:

whoschek.AT.lbl.DOT.gov

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 (Character.isLetter(c))
static Pattern	WHITESPACE_PATTERN "\\s+"; Divides text at whitespaces (Character.isWhitespace(c))

Constructor Summary

PatternAnalyzer(Pattern pattern, boolean toLowerCase, Set stopWords)
Constructs a new instance with the given parameters.

Method Summary

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

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

getPositionIncrementGap

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 (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(Pattern pattern,
                       boolean toLowerCase,
                       Set stopWords)

Constructs a new instance with the given parameters.

Parameters:

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(String[])and/or WordlistLoaderas in WordlistLoader.getWordSet(new File("samples/fulltext/stopwords.txt") or other stop words lists .

Method Detail

tokenStream

public TokenStream tokenStream(String fieldName,
                               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).

text - the string to tokenize

Returns:

a new token stream

tokenStream

public TokenStream tokenStream(String fieldName,
                               Reader reader)

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

Specified by:

tokenStream in class Analyzer

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.