How can I configure DataBinder to use a specific Locale to match a comma as decimal separator?

Question

I use a DataBinder to map values to objects like this:

final var binder = new DataBinder(target);
binder.setIgnoreUnknownFields(false);
binder.bind(new MutablePropertyValues(properties));

Now I have some strings which have a comma as decimal separator and need to be converted into a double.

This gives me the following error because "0,00" can not be converted into a double:

Field error in object 'target' on field 'price': rejected value [0,00];
codes [typeMismatch.target.price,typeMismatch.price,typeMismatch.double,typeMismatch];
arguments [org.springframework.context.support.DefaultMessageSourceResolvable:
codes [target.price,price]; arguments []; default message [price]]; default message
[Failed to convert property value of type 'java.lang.String' to required type 'double'
for property 'price'; nested exception is java.lang.NumberFormatException: For input string: "0,00"]

I don't know how to make DataBinder to accept the comma as decimal separator or use the locale Locale.FR (which is the data source locale).

This didn't help:

LocaleContextHolder.setLocale(Locale.FRANCE);
Locale.setDefault(Locale.FRANCE);

Can someone tell me how to handle the decimal comma?

This is my test case:

class DataBinderTest {

    class Foo {
        public double price;
        public void setPrice(double price) {
            this.price=price;
        }
    }

    @Test
    void testMapping() throws BindException {
        final var properties = new Properties();
        properties.setProperty("price","0,00");

        final var binder = new DataBinder(new Foo());
        binder.setIgnoreUnknownFields(false);
        binder.bind(new MutablePropertyValues(properties));
        if (binder.getBindingResult().hasErrors()) {
            throw new BindException(binder.getBindingResult());
        }
    }
}

score 0 · Answer 1 · answered Sep 14 '21 at 12:26

The solution is to register a custom editor like this:

binder.registerCustomEditor(Double.class,
    new CustomNumberEditor(Double.class, NumberFormat.getInstance(Locale.FRANCE), true));

where the boolean parameter tells if an empty string should be accepted and converted into null. (Note: true of course this wont work with the primitive type double)

How can I configure DataBinder to use a specific Locale to match a comma as decimal separator?

1 Answers1