Treat string as ordinal of enum if it's numeric

Fix GH-25543

spring-core/src/main/java/org/springframework/core/convert/support/StringToEnumConverterFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -25,6 +25,7 @@
  *
  * @author Keith Donald
  * @author Stephane Nicoll
+ * @author Yanming Zhou
  * @since 3.0
  */
 @SuppressWarnings({"rawtypes", "unchecked"})
@@ -51,6 +52,10 @@ public T convert(String source) {
 				// It's an empty enum identifier: reset the enum value to null.
 				return null;
 			}
+			if (source.chars().allMatch(Character::isDigit)) {
+				// It's safe to use source as ordinal since name cannot be numeric.
+				return this.enumType.getEnumConstants()[Integer.parseInt(source)];
+			}
 			return (T) Enum.valueOf(this.enumType, source.trim());
 		}
 	}

spring-core/src/test/java/org/springframework/core/convert/support/GenericConversionServiceTests.java

@@ -503,6 +503,12 @@ void stringToEnumWithBaseInterfaceConversion() {
 		assertThat(conversionService.convert("base1", MyEnum.class)).isEqualTo(MyEnum.A);
 	}
 
+	@Test
+	void stringToEnumWithOrdinalAsString() {
+		conversionService.addConverterFactory(new StringToEnumConverterFactory());
+		assertThat(conversionService.convert("0", MyEnum.class)).isEqualTo(MyEnum.A);
+	}
+
 	@Test
 	void convertNullAnnotatedStringToString() throws Exception {
 		String source = null;