From 89d2bd954ab99cc4ad93ccb15f632693675ef712 Mon Sep 17 00:00:00 2001
From: Juergen Hoeller <jhoeller@pivotal.io>
Date: Tue, 30 Jan 2018 15:53:58 +0100
Subject: [PATCH] Properly analyze Java 9 class cast messages for lambda event
 listeners

Issue: SPR-16435
---
 .../SimpleApplicationEventMulticaster.java    | 19 ++++++++++++--
 .../event/ApplicationContextEventTests.java   | 26 ++++++++++++++++++-
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/spring-context/src/main/java/org/springframework/context/event/SimpleApplicationEventMulticaster.java b/spring-context/src/main/java/org/springframework/context/event/SimpleApplicationEventMulticaster.java
index eca9ff7b1ba..eace00211a0 100644
--- a/spring-context/src/main/java/org/springframework/context/event/SimpleApplicationEventMulticaster.java
+++ b/spring-context/src/main/java/org/springframework/context/event/SimpleApplicationEventMulticaster.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.
@@ -173,8 +173,9 @@ public class SimpleApplicationEventMulticaster extends AbstractApplicationEventM
 		}
 		catch (ClassCastException ex) {
 			String msg = ex.getMessage();
-			if (msg == null || msg.startsWith(event.getClass().getName())) {
+			if (msg == null || matchesClassCastMessage(msg, event.getClass().getName())) {
 				// Possibly a lambda-defined listener which we could not resolve the generic event type for
+				// -> let's suppress the exception and just log a debug message.
 				Log logger = LogFactory.getLog(getClass());
 				if (logger.isDebugEnabled()) {
 					logger.debug("Non-matching event type for listener: " + listener, ex);
@@ -186,4 +187,18 @@ public class SimpleApplicationEventMulticaster extends AbstractApplicationEventM
 		}
 	}
 
+	private boolean matchesClassCastMessage(String classCastMessage, String eventClassName) {
+		// On Java 8, the message simply starts with the class name: "java.lang.String cannot be cast..."
+		if (classCastMessage.startsWith(eventClassName)) {
+			return true;
+		}
+		// On Java 9, the message contains the module name: "java.base/java.lang.String cannot be cast..."
+		int moduleSeparatorIndex = classCastMessage.indexOf('/');
+		if (moduleSeparatorIndex != -1 && classCastMessage.startsWith(eventClassName, moduleSeparatorIndex + 1)) {
+			return true;
+		}
+		// Assuming an unrelated class cast failure...
+		return false;
+	}
+
 }
diff --git a/spring-context/src/test/java/org/springframework/context/event/ApplicationContextEventTests.java b/spring-context/src/test/java/org/springframework/context/event/ApplicationContextEventTests.java
index e1c778ad8c5..f7fb80595fc 100644
--- a/spring-context/src/test/java/org/springframework/context/event/ApplicationContextEventTests.java
+++ b/spring-context/src/test/java/org/springframework/context/event/ApplicationContextEventTests.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.
@@ -472,6 +472,30 @@ public class ApplicationContextEventTests extends AbstractApplicationEventListen
 		context.close();
 	}
 
+	@Test
+	public void lambdaAsListenerWithJava8StyleClassCastMessage() {
+		StaticApplicationContext context = new StaticApplicationContext();
+		ApplicationListener<ApplicationEvent> listener =
+				event -> { throw new ClassCastException(event.getClass().getName()); };
+		context.addApplicationListener(listener);
+		context.refresh();
+
+		context.publishEvent(new MyEvent(context));
+		context.close();
+	}
+
+	@Test
+	public void lambdaAsListenerWithJava9StyleClassCastMessage() {
+		StaticApplicationContext context = new StaticApplicationContext();
+		ApplicationListener<ApplicationEvent> listener =
+				event -> { throw new ClassCastException("spring.context/" + event.getClass().getName()); };
+		context.addApplicationListener(listener);
+		context.refresh();
+
+		context.publishEvent(new MyEvent(context));
+		context.close();
+	}
+
 	@Test
 	public void beanPostProcessorPublishesEvents() {
 		GenericApplicationContext context = new GenericApplicationContext();