Module org.apache.lucene.analysis.common

Package org.apache.lucene.analysis.de

Class GermanStemFilter

java.lang.Object

org.apache.lucene.util.AttributeSource

org.apache.lucene.analysis.TokenStream

org.apache.lucene.analysis.TokenFilter

org.apache.lucene.analysis.de.GermanStemFilter

All Implemented Interfaces:

Closeable, AutoCloseable, Unwrappable<TokenStream>

public final class GermanStemFilter
extends TokenFilter

A TokenFilter that stems German words.

It supports a table of words that should not be stemmed at all. The stemmer used can be changed at runtime after the filter object is created (as long as it is a GermanStemmer).

To prevent terms from being stemmed use an instance of SetKeywordMarkerFilter or a custom TokenFilter that sets the KeywordAttribute before this TokenStream.

See Also:

• SetKeywordMarkerFilter

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource

AttributeSource.State

Field Summary

Fields

Modifier and Type	Field	Description
private final KeywordAttribute	keywordAttr
private GermanStemmer	stemmer	The actual token in the input stream.
private final CharTermAttribute	termAtt

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

input

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

DEFAULT_TOKEN_ATTRIBUTE_FACTORY

Constructor Summary

Constructors

Constructor	Description
GermanStemFilter(TokenStream in)	Creates a GermanStemFilter instance

Method Summary

Modifier and Type	Method	Description
boolean	incrementToken()	Consumers (i.e., IndexWriter) use this method to advance the stream to the next token.
void	setStemmer(GermanStemmer stemmer)	Set a alternative/custom GermanStemmer for this filter.

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

close, end, reset, unwrap

Methods inherited from class org.apache.lucene.util.AttributeSource

addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, endAttributes, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, removeAllAttributes, restoreState, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Details

stemmer

private GermanStemmer stemmer

The actual token in the input stream.

termAtt

private final CharTermAttribute termAtt

keywordAttr

private final KeywordAttribute keywordAttr

Constructor Details

GermanStemFilter

public GermanStemFilter(TokenStream in)

Creates a GermanStemFilter instance

Parameters:

in - the source TokenStream

Method Details

incrementToken

public boolean incrementToken()
                       throws IOException

Description copied from class: TokenStream

Consumers (i.e., IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate AttributeImpls with the attributes of the next token.

The producer must make no assumptions about the attributes after the method has been returned: the caller may arbitrarily change it. If the producer needs to preserve the state for subsequent calls, it can use AttributeSource.captureState() to create a copy of the current attribute state.

This method is called for every token of a document, so an efficient implementation is crucial for good performance. To avoid calls to AttributeSource.addAttribute(Class) and AttributeSource.getAttribute(Class), references to all AttributeImpls that this stream uses should be retrieved during instantiation.

To ensure that filters and consumers know which attributes are available, the attributes must be added during instantiation. Filters and consumers are not required to check for availability of attributes in TokenStream.incrementToken().

Specified by:

incrementToken in class TokenStream

Returns:

Returns true for next token in the stream, or false at EOS

Throws:

IOException

setStemmer

public void setStemmer(GermanStemmer stemmer)

Set a alternative/custom GermanStemmer for this filter.