private String readNumber(InputStream is) throws Exception {
        StringBuilder sb = new StringBuilder();
        while (is.available() > 0) {
            is.mark(1);
            char c = (char) is.read();
            if (!isNumeric(c)) {
                is.reset();
                break;
            } else {
                sb.append(c);
            }
        }
        return sb.toString().trim();
    }
Constant value can be:

<ol>
  <li>List of values (a,b,c)
  <li>Range of values (m AND n)
  <li>A value (x)
  <li>A value is either a string or a number
</ol>
es6-persistence/src/main/java/com/netflix/conductor/es6/dao/query/parser/internal/ConstValue.java