Use canonical names for types in synthesized annotation toString

My proposal for the same change in the JDK is currently targeted for
JDK 19.

- https://bugs.openjdk.java.net/browse/JDK-8281462
- https://bugs.openjdk.java.net/browse/JDK-8281568
- openjdk/jdk#7418

See spring-projectsgh-28015

spring-core/src/main/java/org/springframework/core/annotation/SynthesizedMergedAnnotationInvocationHandler.java

@@ -177,7 +177,7 @@ private int getValueHashCode(Object value) {
 	private String annotationToString() {
 		String string = this.string;
 		if (string == null) {
-			StringBuilder builder = new StringBuilder("@").append(this.type.getName()).append('(');
+			StringBuilder builder = new StringBuilder("@").append(getName(this.type)).append('(');
 			for (int i = 0; i < this.attributes.size(); i++) {
 				Method attribute = this.attributes.get(i);
 				if (i > 0) {
@@ -202,7 +202,7 @@ private String toString(Object value) {
 			return ((Enum<?>) value).name();
 		}
 		if (value instanceof Class) {
-			return ((Class<?>) value).getName() + ".class";
+			return getName((Class<?>) value) + ".class";
 		}
 		if (value.getClass().isArray()) {
 			StringBuilder builder = new StringBuilder("{");
@@ -277,6 +277,11 @@ static <A extends Annotation> A createProxy(MergedAnnotation<A> annotation, Clas
 		return (A) Proxy.newProxyInstance(classLoader, interfaces, handler);
 	}
 
+	private static String getName(Class<?> clazz) {
+		String canonicalName = clazz.getCanonicalName();
+		return (canonicalName != null ? canonicalName : clazz.getName());
+	}
+
 
 	private static boolean isVisible(ClassLoader classLoader, Class<?> interfaceClass) {
 		if (classLoader == interfaceClass.getClassLoader()) {

spring-core/src/test/java/org/springframework/core/annotation/MergedAnnotationsTests.java

@@ -1887,15 +1887,22 @@ private void assertToStringForWebMappingWithPathAndValue(RequestMapping webMappi
 
 		// Formatting common to Spring and JDK 9+
 		assertThat(string)
-			.startsWith("@" + RequestMapping.class.getName() + "(")
-			.contains("value={\"/test\"}", "path={\"/test\"}", "name=\"bar\"", "clazz=java.lang.Object.class")
+			.contains("value={\"/test\"}", "path={\"/test\"}", "name=\"bar\"")
 			.endsWith(")");
 
 		if (webMapping instanceof SynthesizedAnnotation) {
-			assertThat(string).as("Spring uses Enum#name()").contains("method={GET, POST}");
+			assertThat(string).as("Spring formatting")
+				.startsWith("@org.springframework.core.annotation.MergedAnnotationsTests.RequestMapping(")
+				.contains("method={GET, POST}",
+						"clazz=org.springframework.core.annotation.MergedAnnotationsTests.RequestMethod.class",
+						"classes={org.springframework.core.annotation.MergedAnnotationsTests.RequestMethod.class}");
 		}
 		else {
-			assertThat(string).as("JDK uses Enum#toString()").contains("method={method: get, method: post}");
+			assertThat(string).as("JDK 9-18 formatting")
+				.startsWith("@org.springframework.core.annotation.MergedAnnotationsTests$RequestMapping(")
+				.contains("method={method: get, method: post}",
+						"clazz=org.springframework.core.annotation.MergedAnnotationsTests$RequestMethod.class",
+						"classes={org.springframework.core.annotation.MergedAnnotationsTests$RequestMethod.class}");
 		}
 	}
 
@@ -2989,8 +2996,9 @@ public String toString() {
 
 		RequestMethod[] method() default {};
 
-		// clazz is only used for testing annotation toString() implementations
-		Class<?> clazz() default Object.class;
+		Class<?> clazz() default RequestMethod.class;
+
+		Class<?>[] classes() default {RequestMethod.class};
 	}
 
 	@Retention(RetentionPolicy.RUNTIME)

spring-test/src/test/java/org/springframework/test/context/BootstrapUtilsTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -72,8 +72,8 @@ void resolveTestContextBootstrapperWithDoubleMetaBootstrapWithAnnotations() {
 		assertThatIllegalStateException().isThrownBy(() ->
 				resolveTestContextBootstrapper(bootstrapContext))
 			.withMessageContaining("Configuration error: found multiple declarations of @BootstrapWith")
-			.withMessageContaining(FooBootstrapper.class.getName())
-			.withMessageContaining(BarBootstrapper.class.getName());
+			.withMessageContaining(FooBootstrapper.class.getCanonicalName())
+			.withMessageContaining(BarBootstrapper.class.getCanonicalName());
 	}
 
 	@Test