Package org.hibernate.search.engine.search.projection.spi

Interface ProjectionAccumulator<E,V,A,R>

Type Parameters:
E - The type of extracted values to accumulate before being transformed.
V - The type of values to accumulate obtained by transforming extracted values (E).
A - The type of the temporary storage for accumulated values, before and after being transformed.
R - The type of the final result containing values of type V.
public interface ProjectionAccumulator<E,V,A,R>
A variation on Collector suitable for projections on field values.

Compared to Collector:

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Interface
    Description
    static interface 
    ProjectionAccumulator.Provider<U,R>
    Provides an accumulator for a given type of values to accumulate (T).

  • Method Summary

    Modifier and Type
    Method
    Description
    A
    accumulate(A accumulated, E value)
    Folds a new value in the given accumulated container.
    default A
    accumulateAll(A accumulated, Collection<E> values)
    Folds a collection of new values in the given accumulated container.
    A
    createInitial()
    Creates the initial accumulated container.
    R
    finish(A accumulated)
    Finishes the accumulation, converting the accumulated container into the final result.
    E
    get(A accumulated, int index)
    Retrieves the value at the given index.
    static <V> ProjectionAccumulator.Provider<V,List<V>>
    list()
     
    static <V> ProjectionAccumulator.Provider<V,V>
    single()
     
    int
    size(A accumulated)
     
    A
    transform(A accumulated, int index, V transformed)
    Transforms the value at the given index, replacing it with the given transformed value.
    default A
    transformAll(A accumulated, ProjectionConverter<? super E,? extends V> converter, FromDocumentValueConvertContext context)
    Transforms all values with the given converter and the given context.

  • Method Details

    • single

      static <V> ProjectionAccumulator.Provider<V,V> single()

    • list

      static <V> ProjectionAccumulator.Provider<V,List<V>> list()

    • createInitial

      A createInitial()
      Creates the initial accumulated container.

      This operation should be non-blocking.

      Returns:
      The initial accumulated container, to pass to the first call to accumulate(Object, Object).

    • accumulate

      A accumulate(A accumulated, E value)
      Folds a new value in the given accumulated container.

      This operation should be non-blocking.

      Parameters:
      accumulated - The accumulated value so far. For the first call, this is a value returned by createInitial(). For the next calls, this is the value returned by the previous call to accumulate(Object, Object).
      value - The value to accumulate.
      Returns:
      The new accumulated value.

    • accumulateAll

      default A accumulateAll(A accumulated, Collection<E> values)
      Folds a collection of new values in the given accumulated container.

      This operation should be non-blocking.

      Parameters:
      accumulated - The accumulated value so far. For the first call, this is a value returned by createInitial(). For the next calls, this is the value returned by the previous call to accumulate(Object, Object).
      values - The values to accumulate.
      Returns:
      The new accumulated value.

    • size

      int size(A accumulated)
      Parameters:
      accumulated - The accumulated value so far, returned by the last call to accumulate(Object, Object).
      Returns:
      The number of elements in the accumulated value.

    • get

      E get(A accumulated, int index)
      Retrieves the value at the given index.

      This operation should be non-blocking.

      Parameters:
      accumulated - The accumulated value so far, returned by the last call to accumulate(Object, Object).
      index - The index of the value to retrieve.
      Returns:
      The value at the given index.

    • transform

      A transform(A accumulated, int index, V transformed)
      Transforms the value at the given index, replacing it with the given transformed value.

      This operation should be non-blocking.

      Parameters:
      accumulated - The accumulated value so far, returned by the last call to accumulate(Object, Object).
      index - The index of the value being transformed.
      transformed - The transformed value.
      Returns:
      The new accumulated value.

    • transformAll

      default A transformAll(A accumulated, ProjectionConverter<? super E,? extends V> converter, FromDocumentValueConvertContext context)
      Transforms all values with the given converter and the given context.

      This operation may be blocking.

      Parameters:
      accumulated - The accumulated value so far, returned by the last call to accumulate(Object, Object).
      converter - The projection converter (from F to V).
      context - The context to be passed to the projection converter.
      Returns:
      The new accumulated value.

    • finish

      R finish(A accumulated)
      Finishes the accumulation, converting the accumulated container into the final result.

      This operation may be blocking.

      Parameters:
      accumulated - The temporary storage created by createInitial(), then populated by successive calls to accumulate(Object, Object), then transformed by a single call to transformAll(Object, ProjectionConverter, FromDocumentValueConvertContext) or by successive calls to transform(Object, int, Object).
      Returns:
      The final result of the accumulation.