Add new method isStateMachineManaged

Determines if the given machine identifier denotes a known managed state machine.

spring-statemachine-core/src/main/java/org/springframework/statemachine/service/DefaultStateMachineService.java

@@ -128,6 +128,18 @@ public class DefaultStateMachineService<S, E> implements StateMachineService<S,
 		}
 	}
 
+	/**
+	 * Determines if the given machine identifier denotes a known managed state machine.
+	 *
+	 * @param machineId machine identifier
+	 * @return true if machineId denotes a known managed state machine currently in memory
+	 */
+	public boolean hasStateMachine(String machineId) {
+		synchronized (machines) {
+			return machines.containsKey(machineId);
+		}
+	}
+
 	/**
 	 * Sets the state machine persist.
 	 *