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

Interface ValueState<T>

  • Type Parameters:
    T - Type of the value in the state.
    All Superinterfaces:
    State
    @PublicEvolving
public interface ValueState<T>
extends State
    State interface for partitioned single-value state. The value can be retrieved or updated.

    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 update​(T value)
      Updates the operator state accessible by value() to the given value.
      T value()
      Returns the current value for the state.

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

        clear

    • Method Detail

      • value

        T value()
 throws IOException
        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.

        If you didn't specify a default value when creating the ValueStateDescriptor this will return null when no value was previously set using update(Object).

        Returns:
        The state value corresponding to the current input.
        Throws:
        IOException - Thrown if the system cannot access the state.

      • update

        void update​(T value)
     throws IOException
        Updates the operator state accessible by value() to the given value. The next time value() is called (for the same state partition) the returned state will represent the updated value. When a partitioned state is updated with null, the state for the current key will be removed and the default value is returned on the next access.
        Parameters:
        value - The new value for the state.
        Throws:
        IOException - Thrown if the system cannot access the state.