Object formatter using reflection
It's pretty nice IMO but can be improved.

If your project uses apache commons (this library is often included), you should consider using the FieldUtils class to get the fields : https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/reflect/FieldUtils.html

Notably, the getFieldsWithAnnotation method would reduce your code complexity by a bit.

That's up to you though ;)

This part :

try {
    String value = field.get(object).toString();
    string += varName + "=" + value + ", ";
} catch (IllegalAccessException e) {
    e.printStackTrace();
    string += varName + "=" + "{Unavailable}, ";
}


may fail if your field is null, you should exploit the String + operator to avoid it like this :

string += varName + "=" + field.get(object) + ", ";


string is really a bad name for your variable, maybe rename it as res or something ?

I'm no big fan of the printStackTrace, you should consider using the various logging utilities proposed by java : https://docs.oracle.com/javase/9/docs/api/java/util/logging/Logger.html or slf4j.

I think those 4 modifications will already make the code neater but we can do a bigger refactoring :
instead of using a String that we concatenate bit by bit and then remove the final comma, you should consider using a Stream over the fields array and generating the result with the Collectors#joining method.

In the end, you'd have the following method :

private static final String SEPARATOR = ", ";

public static String format(Object object) {
    final String className = object.getClass().getSimpleName();
    final String prefix = className + "[";
    String res = Arrays.stream(FieldUtils.getFieldsWithAnnotation(object.getClass(), Formatted.class))
        .map(field -&gt; {
        String varName = field.getName();
        try {
            return varName + "=" + field.get(object);
        } catch (IllegalAccessException e) {
            log.severe(e.toString());
            return varName + "=" + "{Unavailable}";
        }
    }).collect(joining(SEPARATOR));
    return prefix + res + "]";
}