JapaneseNumberFilter (Lucene 10.5.0 kuromoji API)
Description: declaration: package: org.apache.lucene.analysis.ja, class: JapaneseNumberFilter

Package org.apache.lucene.analysis.ja

# Class JapaneseNumberFilter

java.lang.Object
org.apache.lucene.util.AttributeSource
org.apache.lucene.analysis.TokenStream
org.apache.lucene.analysis.TokenFilter
org.apache.lucene.analysis.ja.JapaneseNumberFilter

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

public class JapaneseNumberFilter extends TokenFilter
A `TokenFilter` that normalizes Japanese numbers (kansūji) to regular Arabic decimal numbers in half-width characters.

Japanese numbers are often written using a combination of kanji and Arabic numbers with various kinds punctuation. For example, ３．２千 means 3200. This filter does this kind of normalization and allows a search for 3200 to match ３．２千 in text, but can also be used to make range facets based on the normalized numbers and so on.

Notice that this analyzer uses a token composition scheme and relies on punctuation tokens being found in the token stream. Please make sure your `JapaneseTokenizer` has `discardPunctuation` set to false. In case punctuation characters, such as ． (U+FF0E FULLWIDTH FULL STOP), is removed from the token stream, this filter would find input tokens ３ and ２千 and give outputs 3 and 2000 instead of 3200, which is likely not the intended result. If you want to remove punctuation characters from your index that are not part of normalized numbers, add a `StopFilter` with the punctuation you wish to remove after `JapaneseNumberFilter` in your analyzer chain.

Below are some examples of normalizations this filter supports. The input is untokenized text and the result is the single term attribute emitted for the input.

- 〇〇七 becomes 7
- 一〇〇〇 becomes 1000
- 三千2百２十三 becomes 3223
- 兆六百万五千一 becomes 1000006005001
- ３．２千 becomes 3200
- １．２万３４５．６７ becomes 12345.67
- 4,647.100 becomes 4647.1
- 15,7 becomes 157 (be aware of this weakness)

Tokens preceded by a token with `PositionIncrementAttribute` of zero are left untouched and emitted as-is.

This filter does not use any part-of-speech information for its normalization and the motivation for this is to also support n-grammed token streams in the future.

This filter may in some cases normalize tokens that are not numbers in their context. For example, is 田中京一 is a name and means Tanaka Kyōichi, but 京一 (Kyōichi) out of context can strictly speaking also represent the number 10000000000000001. This filter respects the `KeywordAttribute`, which can be used to prevent specific normalizations from happening.

Also notice that token attributes such as `PartOfSpeechAttribute`, `ReadingAttribute`, `InflectionAttribute` and `BaseFormAttribute` are left unchanged and will inherit the values of the last token used to compose the normalized number and can be wrong. Hence, for １０万 (10000), we will have `ReadingAttribute` set to マン. This is a known issue and is subject to a future improvement.

Japanese formal numbers (daiji), accounting numbers and decimal fractions are currently not supported.

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static class`
  `JapaneseNumberFilter.NumberBuffer`
  Buffer that holds a Japanese number string and a position index used as a parsed-to marker

  ## 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
  `JapaneseNumberFilter(TokenStream input)`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `final boolean`
  `incrementToken()`
  `boolean`
  `isArabicNumeral(char c)`
  Arabic numeral predicate.
  `boolean`
  `isNumeral(char c)`
  Numeral predicate
  `boolean`
  `isNumeral(String input)`
  Numeral predicate
  `boolean`
  `isNumeralPunctuation(char c)`
  Numeral punctuation predicate
  `boolean`
  `isNumeralPunctuation(String input)`
  Numeral punctuation predicate
  `String`
  `normalizeNumber(String number)`
  Normalizes a Japanese number
  `BigDecimal`
  `parseLargeKanjiNumeral(JapaneseNumberFilter.NumberBuffer buffer)`
  Parse large kanji numerals (ten thousands or larger)
  `BigDecimal`
  `parseMediumKanjiNumeral(JapaneseNumberFilter.NumberBuffer buffer)`
  Parse medium kanji numerals (tens, hundreds or thousands)
  `void`
  `reset()`

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

  `close, end, 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

  - ### JapaneseNumberFilter

    public JapaneseNumberFilter(TokenStream input)

- ## Method Details

  - ### incrementToken

    public final boolean incrementToken() throws IOException
    Specified by:
      `incrementToken` in class `TokenStream`
    Throws:
      `IOException`

  - ### reset

    public void reset() throws IOException
    Overrides:
      `reset` in class `TokenFilter`
    Throws:
      `IOException`

  - ### normalizeNumber

    public String normalizeNumber(String number)
    Normalizes a Japanese number
    Parameters:
      `number` - number or normalize
    Returns:
      normalized number, or number to normalize on error (no op)

  - ### parseLargeKanjiNumeral

    public BigDecimal parseLargeKanjiNumeral(JapaneseNumberFilter.NumberBuffer buffer)
    Parse large kanji numerals (ten thousands or larger)
    Parameters:
      `buffer` - buffer to parse
    Returns:
      parsed number, or null on error or end of input

  - ### parseMediumKanjiNumeral

    public BigDecimal parseMediumKanjiNumeral(JapaneseNumberFilter.NumberBuffer buffer)
    Parse medium kanji numerals (tens, hundreds or thousands)
    Parameters:
      `buffer` - buffer to parse
    Returns:
      parsed number or null on error

  - ### isNumeral

    public boolean isNumeral(String input)
    Numeral predicate
    Parameters:
      `input` - string to test
    Returns:
      true if and only if input is a numeral

  - ### isNumeral

    public boolean isNumeral(char c)
    Numeral predicate
    Parameters:
      `c` - character to test
    Returns:
      true if and only if c is a numeral

  - ### isNumeralPunctuation

    public boolean isNumeralPunctuation(String input)
    Numeral punctuation predicate
    Parameters:
      `input` - string to test
    Returns:
      true if and only if c is a numeral punctuation string

  - ### isNumeralPunctuation

    public boolean isNumeralPunctuation(char c)
    Numeral punctuation predicate
    Parameters:
      `c` - character to test
    Returns:
      true if and only if c is a numeral punctuation character

  - ### isArabicNumeral

    public boolean isArabicNumeral(char c)
    Arabic numeral predicate. Both half-width and full-width characters are supported
    Parameters:
      `c` - character to test
    Returns:
      true if and only if c is an Arabic numeral