Package org.apache.flink.api.common.state

Interface AppendingState<IN,​OUT>

  • Type Parameters:
    IN - Type of the value that can be added to the state.
    OUT - Type of the value that can be retrieved from the state.
    All Superinterfaces:
    State
    All Known Subinterfaces:
    AggregatingState<IN,​OUT>, ListState<T>, MergingState<IN,​OUT>, ReducingState<T>
    @PublicEvolving
public interface AppendingState<IN,​OUT>
extends State
    Base interface for partitioned state that supports adding elements and inspecting the current state. Elements can either be kept in a buffer (list-like) or aggregated into one value.

    The state is accessed and modified by user functions, and checkpointed consistently by the system as part of the distributed snapshots.

    The state is only accessible by functions applied on a KeyedStream. The key is automatically supplied by the system, so the function always sees the value mapped to the key of the current element. That way, the system can handle stream and state partitioning consistently together.

    • Method Summary

      All Methods Instance Methods Abstract Methods 
      Modifier and Type Method Description
      void add​(IN value)
      Updates the operator state accessible by get() by adding the given value to the list of values.
      OUT get()
      Returns the current value for the state.

      • Methods inherited from interface org.apache.flink.api.common.state.State

        clear

    • Method Detail

      • get

        OUT get()
 throws Exception
        Returns the current value for the state. When the state is not partitioned the returned value is the same for all inputs in a given operator instance. If state partitioning is applied, the value returned depends on the current operator input, as the operator maintains an independent state for each partition.

        NOTE TO IMPLEMENTERS: if the state is empty, then this method should return null.

        Returns:
        The operator state value corresponding to the current input or null if the state is empty.
        Throws:
        Exception - Thrown if the system cannot access the state.

      • add

        void add​(IN value)
  throws Exception
        Updates the operator state accessible by get() by adding the given value to the list of values. The next time get() is called (for the same state partition) the returned state will represent the updated list.

        If null is passed in, the behaviour is undefined (implementation related). TODO: An unified behaviour across all sub-classes.

        Parameters:
        value - The new value for the state.
        Throws:
        Exception - Thrown if the system cannot access the state.