Add event into state context

- This now adds getEvent() into StateContext which
  makes it easier to figure out what caused a transition
  and also makes life easier in actions.

spring-statemachine-core/src/main/java/org/springframework/statemachine/StateContext.java

@@ -30,6 +30,14 @@ import org.springframework.statemachine.transition.Transition;
  */
 public interface StateContext<S, E> {
 
+	/**
+	 * Gets the event associated with a context. Event may be null if transition
+	 * is not triggered by a signal.
+	 * 
+	 * @return the event
+	 */
+	E getEvent();
+	
 	/**
 	 * Gets the event message headers.
 	 *

spring-statemachine-core/src/main/java/org/springframework/statemachine/support/AbstractStateMachine.java

@@ -226,7 +226,7 @@ public abstract class AbstractStateMachine<S, E> extends LifecycleObjectSupport
 		switchToState(initialState, initialEvent, null, this);
 		// TODO: for now execute outside of switchToState
 		if (initialTransition != null) {
-			StateContext<S, E> stateContext = new DefaultStateContext<S, E>(
+			StateContext<S, E> stateContext = new DefaultStateContext<S, E>(initialEvent != null ? initialEvent.getPayload() : null,
 					initialEvent != null ? initialEvent.getHeaders() : null, extendedState, initialTransition, this);
 			initialTransition.transit(stateContext);
 		}
@@ -414,7 +414,8 @@ public abstract class AbstractStateMachine<S, E> extends LifecycleObjectSupport
 			log.trace("Exit state=[" + state + "]");
 			MessageHeaders messageHeaders = event != null ? event.getHeaders() : new MessageHeaders(
 					new HashMap<String, Object>());
-			StateContext<S, E> stateContext = new DefaultStateContext<S, E>(messageHeaders, extendedState, transition, stateMachine);
+			StateContext<S, E> stateContext = new DefaultStateContext<S, E>(event != null ? event.getPayload() : null,
+					messageHeaders, extendedState, transition, stateMachine);
 
 			State<S, E> findDeep = findDeepParent(transition.getTarget());
 			boolean isTargetSubOfOtherState = findDeep != null && findDeep != currentState;
@@ -444,7 +445,8 @@ public abstract class AbstractStateMachine<S, E> extends LifecycleObjectSupport
 			log.trace("Enter state=[" + state + "]");
 			MessageHeaders messageHeaders = event != null ? event.getHeaders() : new MessageHeaders(
 					new HashMap<String, Object>());
-			StateContext<S, E> stateContext = new DefaultStateContext<S, E>(messageHeaders, extendedState, transition, stateMachine);
+			StateContext<S, E> stateContext = new DefaultStateContext<S, E>(event != null ? event.getPayload() : null,
+					messageHeaders, extendedState, transition, stateMachine);
 
 			if (transition != null) {
 				State<S, E> findDeep1 = findDeepParent(transition.getTarget());
@@ -571,7 +573,7 @@ public abstract class AbstractStateMachine<S, E> extends LifecycleObjectSupport
 
 			// go through candidates and transit max one
 			for (Transition<S, E> t : trans) {
-				StateContext<S, E> stateContext = new DefaultStateContext<S, E>(
+				StateContext<S, E> stateContext = new DefaultStateContext<S, E>(queuedEvent != null ? queuedEvent.getPayload() : null,
 						queuedEvent != null ? queuedEvent.getHeaders() : null, extendedState, t, this);
 				if (t == null) {
 					continue;
@@ -607,7 +609,7 @@ public abstract class AbstractStateMachine<S, E> extends LifecycleObjectSupport
 		if (sourceState != null && targetState != null) {
 			MessageHeaders messageHeaders = event != null ? event.getHeaders() : new MessageHeaders(
 					new HashMap<String, Object>());
-			StateContext<S, E> stateContext = new DefaultStateContext<S, E>(messageHeaders, extendedState, null, this);
+			StateContext<S, E> stateContext = new DefaultStateContext<S, E>(event != null ? event.getPayload() : null, messageHeaders, extendedState, null, this);
 			getStateMachineHandlerResults(getStateMachineHandlers(sourceState, targetState), stateContext);
 		}
 	}

spring-statemachine-core/src/main/java/org/springframework/statemachine/support/DefaultStateContext.java

@@ -23,6 +23,8 @@ import org.springframework.statemachine.transition.Transition;
 
 public class DefaultStateContext<S, E> implements StateContext<S, E> {
 
+	private final E event;
+	
 	private final MessageHeaders messageHeaders;
 
 	private final ExtendedState extendedState;
@@ -31,12 +33,18 @@ public class DefaultStateContext<S, E> implements StateContext<S, E> {
 
 	private final StateMachine<S, E> stateMachine;
 
-	public DefaultStateContext(MessageHeaders messageHeaders, ExtendedState extendedState, Transition<S,E> transition, StateMachine<S, E> stateMachine) {
+	public DefaultStateContext(E event, MessageHeaders messageHeaders, ExtendedState extendedState, Transition<S,E> transition, StateMachine<S, E> stateMachine) {
+		this.event = event;
 		this.messageHeaders = messageHeaders;
 		this.extendedState = extendedState;
 		this.transition = transition;
 		this.stateMachine = stateMachine;
 	}
+	
+	@Override
+	public E getEvent() {
+		return event;
+	}
 
 	@Override
 	public MessageHeaders getMessageHeaders() {

spring-statemachine-core/src/test/java/org/springframework/statemachine/docs/DocsConfigurationSampleTests.java

@@ -25,6 +25,8 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.statemachine.AbstractStateMachineTests;
 import org.springframework.statemachine.StateContext;
 import org.springframework.statemachine.StateMachine;
@@ -313,5 +315,24 @@ public class DocsConfigurationSampleTests extends AbstractStateMachineTests {
 	public static class Config9 extends EnumStateMachineConfigurerAdapter<States, Events> {
 	}
 // end::snippetN[]
+	
+	static class DummyShowSendEvent {
+		
+// tag::snippetO[]
+		@Autowired
+		StateMachine<States, Events> stateMachine;
+		
+		void signalMachine() {
+			stateMachine.sendEvent(Events.E1);
+			
+			Message<Events> message = MessageBuilder
+					.withPayload(Events.E2)
+					.setHeader("foo", "bar")
+					.build();
+			stateMachine.sendEvent(message);
+		}
+// end::snippetO[]
+		
+	}
 
 }

spring-statemachine-core/src/test/java/org/springframework/statemachine/guard/SpelExpressionGuardTests.java

@@ -59,7 +59,7 @@ public class SpelExpressionGuardTests extends AbstractStateMachineTests {
 		Map<String, Object> map = new HashMap<String, Object>();
 		map.put("foo", "bar");
 		MessageHeaders headers = new MessageHeaders(map);
-		DefaultStateContext<TestStates, TestEvents> stateContext = new DefaultStateContext<TestStates, TestEvents>(headers, null, null, null);
+		DefaultStateContext<TestStates, TestEvents> stateContext = new DefaultStateContext<TestStates, TestEvents>(null, headers, null, null, null);
 
 		assertThat(guard.evaluate(stateContext), is(true));
 	}