Be defensive when clearing caches for restart

Update `Restarter` to be much more defensive when attempting to clear
caches. We now use `clearCache()` methods whenever possible, and only
fall back to field access when absolutely necessary. In addition field
access now ignore any exceptions.

Fixes gh-12719

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/Restarter.java

 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -341,16 +341,47 @@ public class Restarter {
 	private void cleanupKnownCaches() throws Exception {
 		// Whilst not strictly necessary it helps to cleanup soft reference caches
 		// early rather than waiting for memory limits to be reached
+		clearResolvableTypeCache();
+		clearCachedIntrospectionResultsCache();
+		clearReflectionUtilsCache();
+		clearAnnotationUtilsCache();
+		clear("com.sun.naming.internal.ResourceManager", "propertiesCache");
+	}
+
+	private void clearResolvableTypeCache() throws Exception {
+		try {
+			ResolvableType.clearCache();
+		}
+		catch (Throwable ex) {
 			clear(ResolvableType.class, "cache");
 			clear("org.springframework.core.SerializableTypeWrapper", "cache");
+		}
+	}
+
+	private void clearCachedIntrospectionResultsCache() throws Exception {
 		clear(CachedIntrospectionResults.class, "acceptedClassLoaders");
 		clear(CachedIntrospectionResults.class, "strongClassCache");
 		clear(CachedIntrospectionResults.class, "softClassCache");
+	}
+
+	private void clearReflectionUtilsCache() throws Exception {
+		try {
+			ReflectionUtils.clearCache();
+		}
+		catch (Throwable ex) {
 			clear(ReflectionUtils.class, "declaredFieldsCache");
 			clear(ReflectionUtils.class, "declaredMethodsCache");
+		}
+	}
+
+	private void clearAnnotationUtilsCache() throws Exception {
+		try {
+			AnnotationUtils.clearCache();
+		}
+		catch (Throwable ex) {
 			clear(AnnotationUtils.class, "findAnnotationCache");
 			clear(AnnotationUtils.class, "annotatedInterfaceCache");
-		clear("com.sun.naming.internal.ResourceManager", "propertiesCache");
+		}
 	}
 
 	private void clear(String className, String fieldName) {
@@ -363,6 +394,7 @@ public class Restarter {
 	}
 
 	private void clear(Class<?> type, String fieldName) throws Exception {
+		try {
 			Field field = type.getDeclaredField(fieldName);
 			field.setAccessible(true);
 			Object instance = field.get(null);
@@ -371,7 +403,8 @@ public class Restarter {
 			}
 			if (instance instanceof Map) {
 				Map<?, ?> map = ((Map<?, ?>) instance);
-			for (Iterator<?> iterator = map.keySet().iterator(); iterator.hasNext();) {
+				for (Iterator<?> iterator = map.keySet().iterator(); iterator
+						.hasNext();) {
 					Object value = iterator.next();
 					if (value instanceof Class && ((Class<?>) value)
 							.getClassLoader() instanceof RestartClassLoader) {
@@ -381,6 +414,10 @@ public class Restarter {
 				}
 			}
 		}
+		catch (Exception ex) {
+			// Ignore
+		}
+	}
 
 	/**
 	 * Cleanup any soft/weak references by forcing an {@link OutOfMemoryError} error.