Question

Is there a standard or at least widespread implementation of something like String.format, but with named arguments?

I’d like to format a templatized string in a way like that:

Map<String, Object> args = new HashMap<String, Object>();
args.put("PATH", "/usr/bin");
args.put("file", "foo");
String s = someHypotheticalMethod("#{PATH}/ls #{file}");
// "/usr/bin/ls foo"

Technically, it’s almost the same as:

String[] args = new String[] { "/usr/bin", "foo" };
String s = String.format("%1$s/ls %2$s", args);
// "/usr/bin/ls foo"

but with named arguments.

I’m aware of:

• String.format
• Formatter
• MessageFormat

but all of them use ordered or at least numbered arguments, not named ones. I know it’s trivial to implement one, but is there a mechanism I’m looking for in standard Java libraries or at least in Apache Commons / Guava / something similar, without bringing in high-profile template engines?

NOTE: I’m not really interested in full-blown template engines, with features like some imperative / functional logic, flow control, modifiers, sub-templates / inclusions, iterators, etc. Generally the following method is a working 4-line implementation – that’s all I need:

public static String interpolate(String format, Map<String, ? extends Object> args) {
    String out = format;
    for (String arg : args.keySet()) {
        out = Pattern.compile(Pattern.quote("#{" + arg + "}")).
                matcher(out).
                replaceAll(args.get(arg).toString());
    }
    return out;
}

Answer 1

You might also try org.apache.commons.lang3.text.StrSubstitutor if Java 7 is not an option. It does exactly what you want it to do. Whether it’s light-weight might depend on whether you use something else of commons-lang as well.