resolving messages with arguments

Question

I've noticed some strange behaviour when resolving Grails messages using the g.message tag. In my properties file I've defined this message:

deleted={0} has been deleted

If I resolve this with:

Long id = 1878L
message(code: 'festival.deleted', args: [id.toString()])

the result is:

1878 has been deleted

which is what I would have expected. However, if I resolve it with:

Long id = 1878L
message(code: 'festival.deleted', args: [id])

the result is:

1,878 has been deleted

It's not clear to me why the number is formatted as "1,878" before it's substituted into the message. I thought perhaps toString() is called on all message arguments if they're not already of type String, but this doesn't appear to explain this behaviour, because

id.toString() == "1878"

Answer 1

The g.message tag uses Java's MessageFormat to generate the text output. MessageFormat has several default ways of formatting arguments if no argument format is specified. {0} has been deleted says there's an argument but doesn't say how to format it.

If the argument is a String, the string is inserted into the message. If the argument is a Number, NumberFormat is used.

groovy:000> NumberFormat.getInstance().format(1878L)
===> 1,878

There's a nice table in the docs for format() that breaks down what happens in what cases. If you want to use a Long as your argument without calling toString() on it, you can change your argument to {0,number,#} which would be equivalent to

groovy:000> new DecimalFormat("#", DecimalFormatSymbols.getInstance()).format(1878L)
===> 1878