EnumsCaseInsensitive.java

    @Component
    @Order(Ordered.HIGHEST_PRECEDENCE)
    @SuppressWarnings({"unchecked", "rawtypes"})
    static final class StringToEnumConverterFactory implements ConverterFactory<String, Enum> {

        @Override
        public <T extends Enum> Converter<String, T> getConverter(Class<T> targetType) {
            return new StringToEnum(getEnumType(targetType));
        }

        private static Class<?> getEnumType(Class<?> targetType) {
            Class<?> enumType = targetType;
            while (enumType != null && !enumType.isEnum()) {
                enumType = enumType.getSuperclass();
            }
            if (enumType == null) {
                throw new IllegalArgumentException(
                        "The target type " + targetType.getName() + " does not refer to an enum");
            }
            return enumType;
        }

        private class StringToEnum<T extends Enum> implements Converter<String, T> {

            private final Class<T> enumType;

            StringToEnum(Class<T> enumType) {
                this.enumType = enumType;
            }

            @Override
            public T convert(String source) {
                if (source.isEmpty()) {
                    return null;
                }
                return (T) Enum.valueOf(this.enumType, source.trim().toUpperCase());
            }
        }

    }

    @Configuration
    static class WebMvcConfigurer extends WebMvcConfigurerAdapter {

        @Override
        public void addFormatters(FormatterRegistry registry) {
            registry.removeConvertible(String.class, Enum.class);
            registry.addConverterFactory(new StringToEnumConverterFactory());
        }

    }