Module org.apache.lucene.analysis.common
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).

  • Field Details

    • inputNodes

      private final RollingBuffer<FlattenGraphFilter.InputNode> inputNodes

    • outputNodes

      private final RollingBuffer<FlattenGraphFilter.OutputNode> outputNodes

    • posIncAtt

      private final PositionIncrementAttribute posIncAtt

    • posLenAtt

      private final PositionLengthAttribute posLenAtt

    • offsetAtt

      private final OffsetAttribute offsetAtt

    • inputFrom

      private int inputFrom
      Which input node the last seen token leaves from

    • outputFrom

      private int outputFrom
      We are currently releasing tokens leaving from this output node

    • done

      private boolean done

    • lastOutputFrom

      private int lastOutputFrom

    • finalOffset

      private int finalOffset

    • finalPosInc

      private int finalPosInc

    • maxLookaheadUsed

      private int maxLookaheadUsed

    • lastStartOffset

      private int lastStartOffset

  • Constructor Details

    • FlattenGraphFilter

      public FlattenGraphFilter(TokenStream in)

  • Method Details

    • releaseBufferedToken

      private boolean releaseBufferedToken()

    • freeBefore

      private void freeBefore(FlattenGraphFilter.OutputNode output)
      Free inputs nodes before the minimum input node for the given output.
      Parameters:
      output - target output node

    • incrementToken

      public boolean incrementToken() throws IOException
      Description copied from class: TokenStream
      Consumers (i.e., IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate AttributeImpls with the attributes of the next token.

      The producer must make no assumptions about the attributes after the method has been returned: the caller may arbitrarily change it. If the producer needs to preserve the state for subsequent calls, it can use AttributeSource.captureState() to create a copy of the current attribute state.

      This method is called for every token of a document, so an efficient implementation is crucial for good performance. To avoid calls to AttributeSource.addAttribute(Class) and AttributeSource.getAttribute(Class), references to all AttributeImpls that this stream uses should be retrieved during instantiation.

      To ensure that filters and consumers know which attributes are available, the attributes must be added during instantiation. Filters and consumers are not required to check for availability of attributes in TokenStream.incrementToken().

      Specified by:
      incrementToken in class TokenStream
      Returns:
      false for end of stream; true otherwise
      Throws:
      IOException

    • recoverFromHole

      private FlattenGraphFilter.OutputNode recoverFromHole(FlattenGraphFilter.InputNode src, int startOffset, int posinc)

    • end

      public void end() throws IOException
      Description copied from class: TokenFilter
      This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new TokenStream API). Streams implementing the old API should upgrade to use this feature.

      This method can be used to perform any end-of-stream operations, such as setting the final offset of a stream. The final offset of a stream might differ from the offset of the last token eg in case one or more whitespaces followed after the last token, but a WhitespaceTokenizer was used.

      Additionally any skipped positions (such as those removed by a stopfilter) can be applied to the position increment, or any adjustment of other attributes where the end-of-stream value may be important.

      If you override this method, always call super.end().

      NOTE: The default implementation chains the call to the input TokenStream, so be sure to call super.end() first when overriding this method.

      Overrides:
      end in class TokenFilter
      Throws:
      IOException - If an I/O error occurs

    • reset

      public void reset() throws IOException
      Description copied from class: TokenFilter
      This method is called by a consumer before it begins consumption using TokenStream.incrementToken().

      Resets this stream to a clean state. Stateful implementations must implement this method so that they can be reused, just as if they had been created fresh.

      If you override this method, always call super.reset(), otherwise some internal state will not be correctly reset (e.g., Tokenizer will throw IllegalStateException on further usage).

      NOTE: The default implementation chains the call to the input TokenStream, so be sure to call super.reset() when overriding this method.

      Overrides:
      reset in class TokenFilter
      Throws:
      IOException

    • getMaxLookaheadUsed

      public int getMaxLookaheadUsed()
      For testing