Package org.apache.lucene.analysis.icu

# Class ICUFoldingFilter

java.lang.Object
org.apache.lucene.util.AttributeSource
org.apache.lucene.analysis.TokenStream
org.apache.lucene.analysis.TokenFilter
org.apache.lucene.analysis.icu.ICUNormalizer2Filter
org.apache.lucene.analysis.icu.ICUFoldingFilter

All Implemented Interfaces:
  `Closeable`, `AutoCloseable`, `Unwrappable<TokenStream>`

public final class ICUFoldingFilter extends ICUNormalizer2Filter
A TokenFilter that applies search term folding to Unicode text, applying foldings from UTR#30 Character Foldings.

This filter applies the following foldings from the report to unicode text:

- Accent removal
- Case folding
- Canonical duplicates folding
- Dashes folding
- Diacritic removal (including stroke, hook, descender)
- Greek letterforms folding
- Han Radical folding
- Hebrew Alternates folding
- Jamo folding
- Letterforms folding
- Math symbol folding
- Multigraph Expansions: All
- Native digit folding
- No-break folding
- Overline folding
- Positional forms folding
- Small forms folding
- Space folding
- Spacing Accents folding
- Subscript folding
- Superscript folding
- Suzhou Numeral folding
- Symbol folding
- Underline folding
- Vertical forms folding
- Width folding

Additionally, Default Ignorables are removed, and text is normalized to NFKC. All foldings, case folding, and normalization mappings are applied recursively to ensure a fully folded and normalized result.

A normalizer with additional settings such as a filter that lists characters not to be normalized can be passed in the constructor.

## Nested Class Summary

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

`AttributeSource.State`

## Field Summary

Fields
Modifier and Type
Field
Description
`static final com.ibm.icu.text.Normalizer2`
`NORMALIZER`
A normalizer for search term folding to Unicode text, applying foldings from UTR#30 Character Foldings.

### 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
`ICUFoldingFilter(TokenStream input)`
Create a new ICUFoldingFilter on the specified input
`ICUFoldingFilter(TokenStream input, com.ibm.icu.text.Normalizer2 normalizer)`
Create a new ICUFoldingFilter on the specified input with the specified normalizer

## Method Summary

### Methods inherited from class org.apache.lucene.analysis.icu.ICUNormalizer2Filter

`incrementToken`

### 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

### NORMALIZER

public static final com.ibm.icu.text.Normalizer2 NORMALIZER
A normalizer for search term folding to Unicode text, applying foldings from UTR#30 Character Foldings.

## Constructor Details

### ICUFoldingFilter

public ICUFoldingFilter(TokenStream input)
Create a new ICUFoldingFilter on the specified input

### ICUFoldingFilter

public ICUFoldingFilter(TokenStream input, com.ibm.icu.text.Normalizer2 normalizer)
Create a new ICUFoldingFilter on the specified input with the specified normalizer