String.format 或类似格式的正确格式字符串

Question

I'm sure I've seen String.format used like this before:

String.format("Some {1}, {2}, {3}", var1, var2, var3);

Does this ring any bells for anyone? Maybe I'm thinking of C#, is there a way of achieving the same in java?

I know you can do something like:

String.format("Some %s, %d, %s", aString, aNumber, aString)

but the syntax I'm after is for the former...

Answer 1

What you are looking for is MessageFormat , which uses a given format and input parameters, eg

MessageFormat.format("Some {0}, {1}, {2}", var1, var2, var3);

And as already mentioned, String.format can still do the job using the alternate syntax, but it is less powerful in functionality and not what you requested.

Answer 2

I do not like to specify both index of parameter or its type - mainly when throwing exception and preparing message for it. I like way SLF4j does it. So I wrapped org.slf4j.helpers.MessageFormatter like this:

public static String subst(String string, Object...objects) {
    return MessageFormatter.arrayFormat(string, objects).getMessage();
}

Then you can use it like this:

public void main(String[] args) {
    throw new RuntimeException(MyUtils.subst("Problem with A={} and B={}!", a, b));
}

Answer 3

Yes, that's the typical format string of C# . In Java, you can use the latter, that is, String.format("%s %d %d", ...) .

An alternative is to use MessageFormat.format("Some {0}, {1}, {2}", var1, var2, var3) , which uses the .NET curly braces notation, as mentioned by @Tobias, though it requires you to import java.text.MessageFormat . They are also more appropriate for when you are dealing with localized resources, where you typically have external .properties files with messages in the format Error {0} ocurred due to {1} .

Answer 4

If you want to use empty placeholders (without positions), you could write a small utility around Message.format() , like this

    String format(String s, Object... var2) {
        int i = 0;
        while(s.contains("{}")) {
            s = s.replaceFirst(Pattern.quote("{}"), "{"+ i++ +"}");
        }
        return MessageFormat.format(s, var2);
    }

And then, can use it like,

format("Some {} {} {}", var1, var2, var3);