Question

Is there a way to detect a number (java double) being set to NaN in a Freemarker template?

Basically I’d like to do something like:

<#if val?is_nan>
  -
<#else>
   ${val}
</#if>

I tried to convert to string and then check for the \uFFFD character, but fail to do the correct compare here.

I have the impression that my problems come from the way, I give the data to the processing

            Map<String, Object> root = new HashMap<String, Object>();
            root.put("var", objectToRender);
            template.process(root, out);

Where objectToRender is the data structure I use. Perhaps I need to set some special flag for double handling?

Answer 1

Update: Starting from FreeMarker 2.3.20 you can just write val?is_nan. For older versions, see below…

There’s no n?is_nan, but you can create your own method that you can use as isNaN(n):

import java.util.List;

import freemarker.template.TemplateBooleanModel;
import freemarker.template.TemplateMethodModelEx;
import freemarker.template.TemplateModelException;
import freemarker.template.TemplateNumberModel;

public class IsNaNMethod implements TemplateMethodModelEx {

    public static final IsNaNMethod INSTANCE = new IsNaNMethod();

    public Object exec(@SuppressWarnings("rawtypes") List args)
    throws TemplateModelException {
        if (args.size() != 1) {
            throw new TemplateModelException("isNaN needs exactly 1 arguments!");
        }

        Object arg = args.get(0);

        if (arg == null) {
            throw new TemplateModelException(
                    "The argument to the isNaN method must not be null!");
        }

        if (!(arg instanceof TemplateNumberModel)) {
            throw new TemplateModelException(
                    "The argument to the isNaN method must be a number! " +
                    "(The class of the value was: " + arg.getClass().getName() + ")");
        }

        Number n = ((TemplateNumberModel) arg).getAsNumber();
        if (n instanceof Double) {
            return ((Double) n).isNaN()
                    ? TemplateBooleanModel.TRUE : TemplateBooleanModel.FALSE;
        } else if (n instanceof Float) {
            return ((Float) n).isNaN()
                    ? TemplateBooleanModel.TRUE : TemplateBooleanModel.FALSE;
        } else {
            return TemplateBooleanModel.FALSE;
        }
    }

}

Put IsNaNMethod.INSTANCE into the data-model as “isNaN” (or into all data-models with config.setSharderVariable), or just pull it in in an #include-d/#import-ed template with <#assign isNaN = "com.example.IsNaNMethod"?new()>.