What is the alternative for String.format() in GWT? - gwt

Question

While GWT is not emulate all java's core, what can be used as alternative for:
String.format("The answer is - %d", 42)?
What is the ellegant and efficient pattern to inject arguments to message in GWT?

Answer 1

One elegant solution is using SafeHtml templates. You can define multiple such templates in an interface like:
public interface MyTemplates extends SafeHtmlTemplates {
#Template("The answer is - {0}")
SafeHtml answer(int value);
#Template("...")
...
}
And then use them:
public static final MyTemplates TEMPLATES = GWT.create(MyTemplates.class);
...
Label label = new Label(TEMPLATES.answer(42));
While this is a little bit more work to set up, it has the enormous advantage that arguments are automatically HTML-escaped. For more info, see https://developers.google.com/web-toolkit/doc/latest/DevGuideSecuritySafeHtml
If you want to go one step further, and internationalize your messages, then see also https://developers.google.com/web-toolkit/doc/latest/DevGuideI18nMessages#SafeHtmlMessages

Answer 2

You can simply write your own format function instead of doing brain storm.
public static String format(final String format, final String... args,String delimiter) {
String[] split = format.split(delimiter);//in your case "%d" as delimeter
final StringBuffer buffer= new StringBuffer();
for (int i= 0; i< split.length - 1; i+= 1) {
buffer.append(split[i]);
buffer.append(args[i]);
}
buffer.append(split[split.length - 1]);
return buffer.toString();
}

Answer 3

Because most (as in 99.999%) message formats are static, known at compile-time, the way GWT approaches it is to parse them at compile-time.
You'll generally use a Messages subinterface for its ability to localize the message, but you'll sometimes rather need SafeHtmlTemplates.

Answer 4

In the 0.001% when template is not known at compile time you can use Javascript sprintf (see: http://www.diveintojavascript.com/projects/javascript-sprintf) as in:
public static native String format (String format, JsArrayMixed values) /*-{
return vsprintf(format, values);
}-*/;

Answer 5

You can write your own.
I wrote a version that just work with Strings(%s):
public static String format(final String format, final Object... args)
{
checkNotNull(format);
checkNotNull(args);
final String pattern = "%s";
int start = 0, last = 0, argsIndex = 0;
final StringBuilder result = new StringBuilder();
while ((start = format.indexOf(pattern, last)) != -1)
{
if (args.length <= argsIndex)
{
throw new IllegalArgumentException("There is more replace patterns than arguments!");
}
result.append(format.substring(last, start));
result.append(args[argsIndex++]);
last = start + pattern.length();
}
if (args.length > argsIndex)
{
throw new IllegalArgumentException("There is more arguments than replace patterns!");
}
result.append(format.substring(last));
return result.toString();
}

Answer 6

why not writing a method like:
String appendAnswer(int result) {
return "The answer is - " + Integer.toString(result);
}
is resolving your problem because you do nothing like formatting in your code.
if you ever face the problem like converting integer/byte to Hex String you should use:
Integer.toString(int, 16);

Answer 7

I don't know GWT much but I am working on a GWT project and I needed this. While trying some alternatives, I have found that this is working;
import java.text.MessageFormat;
MessageFormat.format("The answer is - {0}", 42);
I don't know if the project's developers added something special to make this work or it is working by default.