org.apache.lucene.analysis.ngram

## Class NGramTokenFilter

- java.lang.Object
- - org.apache.lucene.util.AttributeSource
  - - org.apache.lucene.analysis.TokenStream
    - - org.apache.lucene.analysis.TokenFilter
      - - org.apache.lucene.analysis.ngram.NGramTokenFilter

- All Implemented Interfaces:
    Closeable, AutoCloseable

      public final class NGramTokenFilter
      extends TokenFilter

  Tokenizes the input into n-grams of the given size(s). As of Lucene 4.4, this token filter:
  - handles supplementary characters correctly,
  - emits all n-grams for the same token at the same position,
  - does not modify offsets,
  - sorts n-grams by their offset in the original token first, then increasing length (meaning that "abc" will give "a", "ab", "abc", "b", "bc", "c").

  If you were using this `TokenFilter` to perform partial highlighting, this won't work anymore since this filter doesn't update offsets. You should modify your analysis chain to use `NGramTokenizer`, and potentially override `NGramTokenizer.isTokenChar(int)` to perform pre-tokenization.

- - ### Nested Class Summary

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

      `AttributeSource.State`

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static boolean` | `DEFAULT_PRESERVE_ORIGINAL`

    - ### 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 and Description
    `NGramTokenFilter(TokenStream input, int gramSize)` Creates an NGramTokenFilter that produces n-grams of the indicated size.
    `NGramTokenFilter(TokenStream input, int minGram, int maxGram, boolean preserveOriginal)` Creates an NGramTokenFilter that, for a given input term, produces all contained n-grams with lengths >= minGram and <= maxGram.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `end()`
    `boolean` | `incrementToken()`
    `void` | `reset()`

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

      `close`

    - ### 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 Detail

    - #### DEFAULT_PRESERVE_ORIGINAL

          public static final boolean DEFAULT_PRESERVE_ORIGINAL

      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### NGramTokenFilter

          public NGramTokenFilter(TokenStream input,
                                  int minGram,
                                  int maxGram,
                                  boolean preserveOriginal)

      Creates an NGramTokenFilter that, for a given input term, produces all contained n-grams with lengths >= minGram and <= maxGram. Will optionally preserve the original term when its length is outside of the defined range. Note: Care must be taken when choosing minGram and maxGram; depending on the input token size, this filter potentially produces a huge number of terms.
      Parameters:
        `input` - `TokenStream` holding the input to be tokenized
        `minGram` - the minimum length of the generated n-grams
        `maxGram` - the maximum length of the generated n-grams
        `preserveOriginal` - Whether or not to keep the original term when it is shorter than minGram or longer than maxGram

    - #### NGramTokenFilter

          public NGramTokenFilter(TokenStream input,
                                  int gramSize)

      Creates an NGramTokenFilter that produces n-grams of the indicated size.
      Parameters:
        `input` - `TokenStream` holding the input to be tokenized
        `gramSize` - the size of n-grams to generate.

  - ### Method Detail

    - #### 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`

    - #### end

          public void end()
                   throws IOException

      Overrides:
        `end` in class `TokenFilter`
      Throws:
        `IOException`

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