Spring formatting with Formatting from String to String and spring:eval does not work - spring

Question

I am running a spring 4.0 mvc webapp and want to make use of the formater SPI with a IbanFormatter:
public class IbanFormatter implements Formatter<String>
{
#Override
public String print ( String iban, Locale locale )
{
StringBuilder sb = new StringBuilder(iban);
for (int i = 4; i < sb.length(); i += 5)
{
sb.insert(i, ' ');
}
return sb.toString();
}
#Override
public String parse ( String iban, Locale locale ) throws ParseException
{
return iban.replaceAll("\\s+", "");
}
}
Additionally I have a AnnotationFormaterFactory:
public final class IbanFormatAnnotationFormatterFactory implements AnnotationFormatterFactory<IbanFormat>
{
#Override
public Printer<?> getPrinter ( IbanFormat annotation, Class<?> fieldType )
{
return new IbanFormatter();
}
#Override
public Parser<?> getParser ( IbanFormat annotation, Class<?> fieldType )
{
return new IbanFormatter();
}
#Override
public Set<Class<?>> getFieldTypes ( )
{
HashSet<Class<?>> hashSet = new HashSet<Class<?>>();
hashSet.add(String.class);
return hashSet;
}
}
And an annotation of course:
#Target({ ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER, ElementType.ANNOTATION_TYPE })
#Retention(RetentionPolicy.RUNTIME)
public #interface IbanFormat
{}
With an Object annotated like this:
public class DirectDebitDTO
{
#IbanFormat
private String iban;
}
I registerd this formatter like this:
#Override
protected void addFormatters ( FormatterRegistry registry )
{
registry.addFormatterForFieldAnnotation(new IsoFallbackJodaDateTimeFormatAnnotationFormatterFactory());
registry.addFormatterForFieldAnnotation(new IbanFormatAnnotationFormatterFactory());
}
My DateFormatter seen above works like a charm.
In my jsp I want to show the formatted iban:
IBAN: <spring:eval expression="directDebit.iban" />
It does not work. It just shows unformatted iban. I debugged it and found the reason in line 65 in ExpressionUtils
public static <T> T convertTypedValue(EvaluationContext context, TypedValue typedValue, Class<T> targetType) {
Object value = typedValue.getValue();
if ((targetType == null) || (value != null && ClassUtils.isAssignableValue(targetType, value))) {
return (T) value;
}
if (context != null) {
return (T) context.getTypeConverter().convertValue(value, typedValue.getTypeDescriptor(), TypeDescriptor.valueOf(targetType));
}
throw new EvaluationException("Cannot convert value '" + value + "' to type '" + targetType.getName() + "'");
}
The first if statement is triggered because both values are Strings. No conversion and thus no formatting takes place. So it wouldn't even help to add a Converter
Of course I could change the type of iban from String to an Iban.class just to get type conversion.
For me it looks like a Bug, but havn't found anything about this.
Is this intended behaviour or a bug?