test if string can be converted to a number in FreeMarker

问题

I am trying to test whether a string can be converted into a number in FreeMarker. For example, "123" and "3.14" can be converted, but "foo" can't. I know that I can test for this by using the number method on the string (e.g. "123"?number) and seeing whether it produces an error, but I am looking for a way to test for this without causing an error.

I tried ?matches("^\d+$"), and it works fine for integers, but I am looking for something that works on all numbers.

I can probably do it using a more sophisticated regex, but I am wondering if there is a simpler way.

回答1:

The simpler way is to not do it in FreeMarker :-) This sounds like something controller (or method on model) should be doing rather than view template. That said, you have a few options:

1. Use ?number built-in within <#attempt> / <#recover> block.
2. Write a method in one of your model objects to check whether your string into a number and invoke it from the template.
3. Write a custom directive to do this for you.

来源：https://stackoverflow.com/questions/1474274/test-if-string-can-be-converted-to-a-number-in-freemarker