org.apache.lucene.analysis

Class PorterStemFilter

java.lang.Object

org.apache.lucene.analysis.TokenStream

org.apache.lucene.analysis.TokenFilter

org.apache.lucene.analysis.PorterStemFilter

public final class PorterStemFilter
extends TokenFilter

Transforms the token stream as per the Porter stemming algorithm. Note: the input to the stemming filter must already be in lower case, so you will need to use LowerCaseFilter or LowerCaseTokenizer farther down the Tokenizer chain in order for this to work properly!

To use this filter with other analyzers, you'll want to write an Analyzer class that sets up the TokenStream chain as you want it. To use this with LowerCaseTokenizer, for example, you'd write an analyzer like this:

    class MyAnalyzer extends Analyzer {
      public final TokenStream tokenStream(String fieldName, Reader reader) {
        return new PorterStemFilter(new LowerCaseTokenizer(reader));
      }
    }
    

Field Summary

Fields inherited from class org.apache.lucene.analysis.TokenFilter

input

Constructor Summary

Constructors

Constructor and Description
PorterStemFilter(TokenStream in)

Method Summary

Methods

Modifier and Type	Method and Description
Token	next(Token reusableToken) Returns the next token in the stream, or null at EOS.

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

close, reset

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

next

Methods inherited from class java.lang.Object

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

Constructor Detail

PorterStemFilter

public PorterStemFilter(TokenStream in)

Method Detail

next

public final Token next(Token reusableToken)
                 throws java.io.IOException

Description copied from class: TokenStream

Returns the next token in the stream, or null at EOS. When possible, the input Token should be used as the returned Token (this gives fastest tokenization performance), but this is not required and a new Token may be returned. Callers may re-use a single Token instance for successive calls to this method.

This implicitly defines a "contract" between consumers (callers of this method) and producers (implementations of this method that are the source for tokens):

• A consumer must fully consume the previously returned Token before calling this method again.
• A producer must call Token.clear() before setting the fields in it & returning it

Also, the producer must make no assumptions about a Token after it has been returned: the caller may arbitrarily change it. If the producer needs to hold onto the token for subsequent calls, it must clone() it before storing it. Note that a TokenFilter is considered a consumer.

Overrides:

next in class TokenStream

Parameters:

reusableToken - a Token that may or may not be used to return; this parameter should never be null (the callee is not required to check for null before using it, but it is a good idea to assert that it is not null.)

Returns:

next token in the stream or null if end-of-stream was hit

Throws:

java.io.IOException