Package org.apache.lucene.analysis.miscellaneous

Class TruncateTokenFilter

java.lang.Object

org.apache.lucene.util.AttributeSource

org.apache.lucene.analysis.TokenStream

org.apache.lucene.analysis.TokenFilter

org.apache.lucene.analysis.miscellaneous.TruncateTokenFilter

All Implemented Interfaces:

Closeable, AutoCloseable, Unwrappable<TokenStream>

public final class TruncateTokenFilter
extends TokenFilter

A token filter for truncating the terms into a specific length (number of codepoints). Fixed prefix truncation, as a stemming method, produces good results on Turkish language. It is reported that F5, using first 5 characters, produced best results in Information Retrieval on Turkish Texts

Since Lucene 10.5, the filter is able to correctly handle codepoints and truncates after the given number of codepoints, no longer producing incomplete surrogate pairs. Use the modern factory method truncateAfterCodePoints(TokenStream, int) to enable this mode. Legacy behaviour is still available with truncateAfterChars(TokenStream, int)

Nested Class Summary

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

AttributeSource.State

Field Summary

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
TruncateTokenFilter(TokenStream input, int nChars)	Deprecated. This constructor is deprecated, use truncateAfterChars(TokenStream, int) for backwards compatibility, or truncateAfterCodePoints(TokenStream, int) to be unicode conformant.

Method Summary

Modifier and Type	Method	Description
final boolean	incrementToken()
static TruncateTokenFilter	truncateAfterChars(TokenStream input, int nChars)	Returns a filter with a prefix of nChars Java Characters.
static TruncateTokenFilter	truncateAfterCodePoints(TokenStream input, int nCodePoints)	Returns a filter with a prefix of nCodePoints.

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

Constructor Details

TruncateTokenFilter

@Deprecated
public TruncateTokenFilter(TokenStream input,
 int nChars)

Deprecated.

This constructor is deprecated, use truncateAfterChars(TokenStream, int) for backwards compatibility, or truncateAfterCodePoints(TokenStream, int) to be unicode conformant.

Instantiates filter with a prefix of nChars Java Characters. This may split surrogate pairs.

Method Details

truncateAfterCodePoints

public static TruncateTokenFilter truncateAfterCodePoints(TokenStream input,
 int nCodePoints)

Returns a filter with a prefix of nCodePoints.

truncateAfterChars

public static TruncateTokenFilter truncateAfterChars(TokenStream input,
 int nChars)

Returns a filter with a prefix of nChars Java Characters. This may split surrogate pairs.

incrementToken

public final boolean incrementToken()
                             throws IOException

Specified by:

incrementToken in class TokenStream

Throws:

IOException