如何在Java中将转义小数文本转换回Unicode

Question

A third-party library in our stack is munging strings containing emoji etc like so:

"Ben \\240\\159\\144\\144\\240\\159\\142\\169"

That is, decimal bytes, not hexadecimal shorts.

Surely there is an existing routine to turn this back into a proper Unicode string, but all the discussion I've found about this expects the format \ኯ, not \\123.

Answer 1

I am not aware of any existing routine, but something simple like this should do the job (assuming the input is available as a string):

public static String unEscapeDecimal(String s) {
  try {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    Writer writer = new OutputStreamWriter(baos, "utf-8");
    int pos = 0;
    for (int i = 0; i < s.length(); i++) {
      char c = s.charAt(i);
      if (c == '\\') {
        writer.flush();
        baos.write(Integer.parseInt(s.substring(i+1, i+4)));
        i += 3;
      } else {
        writer.write(c);
      }
    }
    writer.flush();
    return new String(baos.toByteArray(), "utf-8");
  } catch (IOException e) {
    throw new RuntimeException(e);
  }
}

The writer is just used to make sure existing characters in the string with code points > 127 are encoded correctly, should they occur unescaped. If all non-ascii characters are escaped, the byte array output stream should be sufficient.