String param = "x=4&a=&ca=2&acb=3&sign=xxx";

Object result = sortParamByKey(param.split("&"));

public static String sortParamByKey(String[] param) {

        if(param != null) {

            List<String> params = Arrays.asList(param);

            String result = params.stream()

            .collect(Collectors.toMap(v->v.split("=")[0],v->v.substring(v.indexOf("=")+1)))

            .entrySet().stream()

            .filter(e->!(e.getValue()==null || "".equals(e.getValue())))

            .filter(e->!"sign".equalsIgnoreCase(e.getKey()))//sign为key的时候,去除

            .sorted(Map.Entry.comparingByKey())

            .map(e->new StringBuilder(e.getKey()).append("=").append(e.getValue()))

            .collect(Collectors.joining("&"))

            ;

            return result;

        }

        return null;

    }