Do not invoke [Map|Collection].isEmpty() in nullSafeConciseToString()

gh-30810 introduced explicit support for collections and maps in
ObjectUtils.nullSafeConciseToString() by invoking isEmpty() on a Map or
Collection to determine which concise string representation should be
used. However, this caused a regression in which an exception was
thrown if the Map or Collection was a proxy generated by
AbstractFactoryBean to support <util:set />, <util:list />, and
<util:map /> in XML configuration.

This commit addresses this set of regressions by always returning
"[...]" or "{...}" for a Collection or Map, respectively, disregarding
whether the map is empty or not.

Closes gh-31138

spring-core/src/main/java/org/springframework/util/ObjectUtils.java

@@ -70,7 +70,6 @@ public abstract class ObjectUtils {
 	private static final String ARRAY_ELEMENT_SEPARATOR = ", ";
 	private static final Object[] EMPTY_OBJECT_ARRAY = new Object[0];
 	private static final String NON_EMPTY_ARRAY = ARRAY_START + "..." + ARRAY_END;
-	private static final String EMPTY_COLLECTION = "[]";
 	private static final String NON_EMPTY_COLLECTION = "[...]";
 
 
@@ -915,10 +914,9 @@ public static String nullSafeToString(@Nullable short[] array) {
 	 * <li>{@code"Optional[<concise-string>]"} if {@code obj} is a non-empty {@code Optional},
 	 * where {@code <concise-string>} is the result of invoking {@link #nullSafeConciseToString}
 	 * on the object contained in the {@code Optional}</li>
-	 * <li>{@code "{}"} if {@code obj} is an empty array or {@link Map}</li>
-	 * <li>{@code "{...}"} if {@code obj} is a non-empty array or {@link Map}</li>
-	 * <li>{@code "[]"} if {@code obj} is an empty {@link Collection}</li>
-	 * <li>{@code "[...]"} if {@code obj} is a non-empty {@link Collection}</li>
+	 * <li>{@code "{}"} if {@code obj} is an empty array</li>
+	 * <li>{@code "{...}"} if {@code obj} is a {@link Map} or a non-empty array</li>
+	 * <li>{@code "[...]"} if {@code obj} is a {@link Collection}</li>
 	 * <li>{@linkplain Class#getName() Class name} if {@code obj} is a {@link Class}</li>
 	 * <li>{@linkplain Charset#name() Charset name} if {@code obj} is a {@link Charset}</li>
 	 * <li>{@linkplain TimeZone#getID() TimeZone ID} if {@code obj} is a {@link TimeZone}</li>
@@ -953,12 +951,12 @@ public static String nullSafeConciseToString(@Nullable Object obj) {
 		if (obj.getClass().isArray()) {
 			return (Array.getLength(obj) == 0 ? EMPTY_ARRAY : NON_EMPTY_ARRAY);
 		}
-		if (obj instanceof Collection<?> collection) {
-			return (collection.isEmpty() ? EMPTY_COLLECTION : NON_EMPTY_COLLECTION);
+		if (obj instanceof Collection) {
+			return NON_EMPTY_COLLECTION;
 		}
-		if (obj instanceof Map<?, ?> map) {
-			// EMPTY_ARRAY and NON_EMPTY_ARRAY are also used for maps.
-			return (map.isEmpty() ? EMPTY_ARRAY : NON_EMPTY_ARRAY);
+		if (obj instanceof Map) {
+			// NON_EMPTY_ARRAY is also used for maps.
+			return NON_EMPTY_ARRAY;
 		}
 		if (obj instanceof Class<?> clazz) {
 			return clazz.getName();

spring-core/src/test/java/org/springframework/util/ObjectUtilsTests.java

@@ -1052,8 +1052,8 @@ void nullSafeConciseToStringForNonEmptyArrays() {
 		void nullSafeConciseToStringForEmptyCollections() {
 			List<String> list = List.of();
 			Set<Integer> set = Set.of();
-			assertThat(ObjectUtils.nullSafeConciseToString(list)).isEqualTo("[]");
-			assertThat(ObjectUtils.nullSafeConciseToString(set)).isEqualTo("[]");
+			assertThat(ObjectUtils.nullSafeConciseToString(list)).isEqualTo("[...]");
+			assertThat(ObjectUtils.nullSafeConciseToString(set)).isEqualTo("[...]");
 		}
 
 		@Test
@@ -1066,8 +1066,8 @@ void nullSafeConciseToStringForNonEmptyCollections() {
 
 		@Test
 		void nullSafeConciseToStringForEmptyMaps() {
-			Map<String, String> map = new HashMap<String, String>();
-			assertThat(ObjectUtils.nullSafeConciseToString(map)).isEqualTo("{}");
+			Map<String, String> map = Map.of();
+			assertThat(ObjectUtils.nullSafeConciseToString(map)).isEqualTo("{...}");
 		}
 
 		@Test