public static String join(Collection collection, String separator) {
        if (isEmpty(collection)) {
            return StringUtils.EMPTY;
        }
        StringBuilder sb = new StringBuilder();
        for (Object object : collection) {
            if (object != null) {
                String string = StringUtils.toString(object);
                if (string != null) {
                    sb.append(string).append(separator);
                }
            }
        }
        return sb.length() > 0 ? sb.substring(0, sb.length() - separator.length()) : StringUtils.EMPTY;
    }
@Test
    public void join() {
        Assert.assertEquals(CommonUtils.join(null, ","), "");
        Assert.assertEquals(CommonUtils.join(new ArrayList(), ","), "");
        List<String> s = new ArrayList<String>();
        s.add("a");
        s.add("b");
        s.add("c");
        Assert.assertEquals(CommonUtils.join(s, "1"), "a1b1c");
    }