How to develop an Activity Definition in Java

An Activity Definition is a combination of the Temporal Java SDK Activity Class implementing a specially annotated interface.

An Activity interface is annotated with @ActivityInterface and an Activity implementation implements this Activity interface. To handle Activity types that do not have an explicitly registered handler, you can directly implement a dynamic Activity.

@ActivityInterface
public interface GreetingActivities {
    String composeGreeting(String greeting, String language);
}

Each method defined in the Activity interface defines a separate Activity method. You can annotate each method in the Activity interface with the @ActivityMethod annotation, but this is completely optional. The following example uses the @ActivityMethod annotation for the method defined in the previous example.

@ActivityInterface
public interface GreetingActivities {
    @ActivityMethod
    String composeGreeting(String greeting, String language);
}

An Activity implementation is a Java class that implements an Activity annotated interface.

// Implementation for the GreetingActivities interface example from in the previous section
 static class GreetingActivitiesImpl implements GreetingActivities {
    @Override
    public String composeGreeting(String greeting, String name) {
      return greeting + " " + name + "!";
    }
  }

Use DynamicActivity to implement any number of Activity types dynamically. When an Activity implementation that extends DynamicActivity is registered, it is called for any Activity type invocation that doesn't have an explicitly registered handler.

The dynamic Activity interface is implemented with the execute method, as shown in the following example.

 // Dynamic Activity implementation
  public static class DynamicGreetingActivityImpl implements DynamicActivity {
    @Override
    public Object execute(EncodedValues args) {
      String activityType = Activity.getExecutionContext().getInfo().getActivityType();
      return activityType
          + ": "
          + args.get(0, String.class)
          + " "
          + args.get(1, String.class)
          + " from: "
          + args.get(2, String.class);
    }
  }

Use Activity.getExecutionContext() to get information about the Activity type that should be implemented dynamically.