如何生成一个逗号分开的List

public static String commaSeparatedList(Collection ids) {
        if (ids == null) {
            return "";
        }
        StringBuilder sb = new StringBuilder();
        Iterator iter = ids.iterator();
        if (iter.hasNext()) {
            Object o = iter.next(); // can be null sometimes
            sb.append(o.toString());
        }
        while (iter.hasNext()) {
            sb.append(",").append(iter.next().toString());
        }
        return sb.toString();
    }