code: public static String escapeUnicode(String s) {
          int len = s.length();
          int i = 0;
          while (i < len) {
              char ch = s.charAt(i);
              if (ch > 255) {
                  StringBuilder buf = new StringBuilder();
                  buf.append(s.substring(0, i));
                  while (i < len) {
                      ch = s.charAt(i);
                      if (ch > 255) {
                          buf.append("\\u");
                          buf.append(Character.forDigit((ch >> 12) % 16, 16));
                          buf.append(Character.forDigit((ch >>  8) % 16, 16));
                          buf.append(Character.forDigit((ch >>  4) % 16, 16));
                          buf.append(Character.forDigit((ch      ) % 16, 16));
                      } else {
                          buf.append(ch);
                      }
                      i++;
                  }
                  s = buf.toString();
              } else {
                  i++;
              }
          }
          return s;
      }
docs: Escape all unicode characters in string.