org.apache.flink.statefun.sdk.StatefulFunction Maven / Gradle / Ivy
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* to you under the Apache License, Version 2.0 (the
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*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
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*/
package org.apache.flink.statefun.sdk;
import org.apache.flink.statefun.sdk.annotations.Persisted;
import org.apache.flink.statefun.sdk.io.EgressIdentifier;
import org.apache.flink.statefun.sdk.io.Router;
import org.apache.flink.statefun.sdk.state.PersistedValue;
/**
* A {@link StatefulFunction} is a user-defined function that can be invoked with a given input.
* This is the primitive building block for a Stateful Functions application.
*
* Concept
*
* Each individual {@code StatefulFunction} is an uniquely invokable "instance" of a {@link
* FunctionType}. Each function is identified by an {@link Address}, representing the function's
* unique id (a string) within its type. From a user's perspective, it would seem as if for each
* unique function id, there exists a stateful instance of the function that is always available to
* be invoked within a Stateful Functions application.
*
*
Invoking a {@code StatefulFunction}
*
* An individual {@code StatefulFunction} can be invoked with arbitrary input from any another
* {@code StatefulFunction} (including itself), or routed from ingresses via a {@link Router}. To
* invoke a {@code StatefulFunction}, the caller simply needs to know the {@code Address} of the
* target function.
*
*
As a result of invoking a {@code StatefulFunction}, the function may continue to invoke other
* functions, modify its state, or send messages to egresses addressed by an {@link
* EgressIdentifier}.
*
*
State
*
* Each individual {@code StatefulFunction} may have state that is maintained by the system,
* providing exactly-once guarantees. Below is a code example of how to register and access state in
* functions:
*
*
{@code
* public class MyFunction implements StatefulFunction {
*
* {@code @Persisted}
* PersistedValue intState = PersistedValue.of("state-name", Integer.class);
*
* {@code @Override}
* public void invoke(Context context, Object input) {
* Integer stateValue = intState.get();
* //...
* intState.set(1108);
* // send messages using context
* }
* }
* }
*
* @see Address
* @see FunctionType
* @see Persisted
* @see PersistedValue
*/
public interface StatefulFunction {
/**
* Invokes this function with a given input.
*
* @param context context for the current invocation. The provided context instance should not be
* used outside the scope of the current invocation.
* @param input input for the current invocation.
*/
void invoke(Context context, Object input);
}