MvcResult returns asyncResult after asyncDispatch

Issue: SPR-16648

spring-web/src/test/java/org/springframework/mock/web/test/MockAsyncContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,6 +30,7 @@ import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
 import org.springframework.beans.BeanUtils;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.web.util.WebUtils;
 
@@ -43,10 +44,12 @@ public class MockAsyncContext implements AsyncContext {
 
 	private final HttpServletRequest request;
 
+	@Nullable
 	private final HttpServletResponse response;
 
 	private final List<AsyncListener> listeners = new ArrayList<>();
 
+	@Nullable
 	private String dispatchedPath;
 
 	private long timeout = 10 * 1000L;	// 10 seconds is Tomcat's default
@@ -54,7 +57,7 @@ public class MockAsyncContext implements AsyncContext {
 	private final List<Runnable> dispatchHandlers = new ArrayList<>();
 
 
-	public MockAsyncContext(ServletRequest request, ServletResponse response) {
+	public MockAsyncContext(ServletRequest request, @Nullable ServletResponse response) {
 		this.request = (HttpServletRequest) request;
 		this.response = (HttpServletResponse) response;
 	}
@@ -62,7 +65,14 @@ public class MockAsyncContext implements AsyncContext {
 
 	public void addDispatchHandler(Runnable handler) {
 		Assert.notNull(handler, "Dispatch handler must not be null");
-		this.dispatchHandlers.add(handler);
+		synchronized (this) {
+			if (this.dispatchedPath == null) {
+				this.dispatchHandlers.add(handler);
+			}
+			else {
+				handler.run();
+			}
+		}
 	}
 
 	@Override
@@ -71,6 +81,7 @@ public class MockAsyncContext implements AsyncContext {
 	}
 
 	@Override
+	@Nullable
 	public ServletResponse getResponse() {
 		return this.response;
 	}
@@ -91,13 +102,14 @@ public class MockAsyncContext implements AsyncContext {
 	}
 
 	@Override
-	public void dispatch(ServletContext context, String path) {
-		this.dispatchedPath = path;
-		for (Runnable r : this.dispatchHandlers) {
-			r.run();
+	public void dispatch(@Nullable ServletContext context, String path) {
+		synchronized (this) {
+			this.dispatchedPath = path;
+			this.dispatchHandlers.forEach(Runnable::run);
 		}
 	}
 
+	@Nullable
 	public String getDispatchedPath() {
 		return this.dispatchedPath;
 	}