org.apache.beam.sdk.transforms

Annotation Type DoFn.StateId

@Documented
 @Retention(value=RUNTIME)
 @Target(value={FIELD,PARAMETER})
 @Experimental(value=STATE)
public static @interface DoFn.StateId

Annotation for declaring and dereferencing state cells.

To declare a state cell, create a field of type StateSpec annotated with a DoFn.StateId. To use the cell during processing, add a parameter of the appropriate State subclass to your @ProcessElement or @OnTimer method, and annotate it with DoFn.StateId. See the following code for an example:

 new DoFn<KV<Key, Foo>, Baz>() {

   @StateId("my-state-id")
   private final StateSpec<ValueState<MyState>> myStateSpec =
       StateSpecs.value(new MyStateCoder());

   @ProcessElement
   public void processElement(
        @Element InputT element,
       @StateId("my-state-id") ValueState<MyState> myState) {
     myState.read();
     myState.write(...);
   }
 }
 

State is subject to the following validity conditions:

• Each state ID must be declared at most once.
• Any state referenced in a parameter must be declared with the same state type.
• State declarations must be final.

Required Element Summary

Required Elements

Modifier and Type	Required Element and Description
java.lang.String	value The state ID.

Element Detail

value

public abstract java.lang.String value

The state ID.