Implement a function to check if a string/byte array follows utf-8 format

Question

I am trying to solve this interview question.

After given clearly definition of UTF-8 format. ex: 1-byte : 0b0xxxxxxx 2- bytes:.... Asked to wri

Answer 1

the CharsetDecoder might be what you are looking for:

@Test
public void testUTF8() throws CharacterCodingException {
    // the desired charset
    final Charset UTF8 = Charset.forName("UTF-8");
    // prepare decoder
    final CharsetDecoder decoder = UTF8.newDecoder();
    decoder.onMalformedInput(CodingErrorAction.REPORT);
    decoder.onUnmappableCharacter(CodingErrorAction.REPORT);

    byte[] bytes = new byte[48];
    new Random().nextBytes(bytes);
    ByteBuffer buffer = ByteBuffer.wrap(bytes);
    try {
        decoder.decode(buffer);
        fail("Should not be UTF-8");
    } catch (final CharacterCodingException e) {
        // noop, the test should fail here
    }

    final String string = "hallo welt!";
    bytes = string.getBytes(UTF8);
    buffer = ByteBuffer.wrap(bytes);
    final String result = decoder.decode(buffer).toString();
    assertEquals(string, result);
}

so your function might look like that:

public static boolean checkEncoding(final byte[] bytes, final String encoding) {
    final CharsetDecoder decoder = Charset.forName(encoding).newDecoder();
    decoder.onMalformedInput(CodingErrorAction.REPORT);
    decoder.onUnmappableCharacter(CodingErrorAction.REPORT);
    final ByteBuffer buffer = ByteBuffer.wrap(bytes);

    try {
        decoder.decode(buffer);
        return true;
    } catch (final CharacterCodingException e) {
        return false;
    }
}