src/main/java/org/deephacks/tools4j/cli/Validator.java
public void validateArgs(List<Object> args, Object instance, Method m, Command cmd) {
        final Set<ConstraintViolation<Object>> set = validator.validateParameters(instance, m,
                args.toArray());
        final StringBuilder sb = new StringBuilder();
        for (ConstraintViolation<Object> violation : set) {
            final Path path = violation.getPropertyPath();
            final String msg = violation.getMessage();
            String var = path.toString();
            try {
                int pos = Integer.parseInt("" + var.charAt(var.length() - 1));
                Argument arg = cmd.getArguments().get(pos);
                sb.append(arg.getName()).append(" ").append(msg).append(". ");
            } catch (Exception e) {
                sb.append(var).append(" ").append(msg).append(". ");
            }
        }
        if (sb.length() > 0) {
            // is ConstraintViolationException more appropriate,
            // letting user choose their error message?
            throw new ValidationException(ARG_VIOLATION_MSG + ": " + sb.toString());
        }
    }
public void validateArgs(List<Object> args, Object instance, Method m, Command cmd) {
        final Set<ConstraintViolation<Object>> set = validator.validateParameters(instance, m,
                args.toArray());
        final StringBuilder sb = new StringBuilder();
        for (ConstraintViolation<Object> violation : set) {
            final Path path = violation.getPropertyPath();
            final String msg = violation.getMessage();
            String var = path.toString();
            try {
                int pos = Integer.parseInt("" + var.charAt(var.length() - 1));
                Argument arg = cmd.getArguments().get(pos);
                sb.append(arg.getName()).append(" ").append(msg).append(". ");
            } catch (Exception e) {
                sb.append(var).append(" ").append(msg).append(". ");
            }
        }
        if (sb.length() > 0) {
            // is ConstraintViolationException more appropriate,
            // letting user choose their error message?
            throw new ValidationException(ARG_VIOLATION_MSG + ": " + sb.toString());
        }
    }
This method will only be called if we know that JSR 303 1.1 Bean Validation API
and compliant implementation are available on classpath.

Method validation was first introduced in version 1.1