code: public static String right(String str, int len) {
          if (str == null) {
              return null;
          }
          if (len < 0) {
              return "";
          }
          if (str.length() <= len) {
              return str;
          }
          return str.substring(str.length() - len);
      }
docs: <p>Gets the rightmost <code>len</code> characters of a String.</p>
  <p>If <code>len</code> characters are not available, or the String
  is <code>null</code>, the String will be returned without an
  an exception. An exception is thrown if len is negative.</p>
  <pre>
  StringUtils.right(null, *)    = null
  StringUtils.right(*, -ve)     = ""
  StringUtils.right("", *)      = ""
  StringUtils.right("abc", 0)   = ""
  StringUtils.right("abc", 2)   = "bc"
  StringUtils.right("abc", 4)   = "abc"
  </pre>
  
  @param str the String to get the rightmost characters from, may be null
  @param len the length of the required String, must be zero or positive
  @return the rightmost characters, <code>null</code> if null String input