FlattenGraphFilter (Lucene 10.5.1 common API)
Description: declaration: package: org.apache.lucene.analysis.core, class: FlattenGraphFilter

Package org.apache.lucene.analysis.core

# Class FlattenGraphFilter

java.lang.Object
org.apache.lucene.util.AttributeSource
org.apache.lucene.analysis.TokenStream
org.apache.lucene.analysis.TokenFilter
org.apache.lucene.analysis.core.FlattenGraphFilter

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

public final class FlattenGraphFilter extends TokenFilter
Converts an incoming graph token stream, such as one from `SynonymGraphFilter`, into a flat form so that all nodes form a single linear chain with no side paths. Every path through the graph touches every node. This is necessary when indexing a graph token stream, because the index does not save `PositionLengthAttribute` and so it cannot preserve the graph structure. However, at search time, query parsers can correctly handle the graph and this token filter should not be used.

If the graph was not already flat to start, this is likely a lossy process, i.e. it will often cause the graph to accept token sequences it should not, and to reject token sequences it should not.

However, when applying synonyms during indexing, this is necessary because Lucene already does not index a graph and so the indexing process is already lossy (it ignores the `PositionLengthAttribute`).

WARNING: This API is experimental and might change in incompatible ways in the next release.

- ## 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
  `FlattenGraphFilter(TokenStream in)`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `end()`
  `int`
  `getMaxLookaheadUsed()`
  For testing
  `boolean`
  `incrementToken()`
  `void`
  `reset()`

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

  `close, 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

  - ### FlattenGraphFilter

    public FlattenGraphFilter(TokenStream in)

- ## Method Details

  - ### incrementToken

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

  - ### end

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

  - ### reset

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

  - ### getMaxLookaheadUsed

    public int getMaxLookaheadUsed()
    For testing