isUTF8.java

Application.java

public class App {
    static boolean isUTF8(int[] buf) {
        int i = 0;
        int len = buf.length;

        while(i < len) {
            // UTF8-1 = %x00-7F
            if (buf[i] <= 0x7F) {
                i++;

                continue;
            }

            // UTF8-2 = %xC2-DF UTF8-tail
            if (buf[i] >= 0xC2 && buf[i] <= 0xDF) {
                // if(buf[i + 1] >= 0x80 && buf[i + 1] <= 0xBF) {
                if (buf[i + 1] >> 6 == 2) {
                    i += 2;

                    continue;
                } else {
                    return false;
                }
            }

            // UTF8-3 = %xE0 %xA0-BF UTF8-tail
            // UTF8-3 = %xED %x80-9F UTF8-tail
            if (
                    (
                        (buf[i] == 0xE0 && buf[i + 1] >= 0xA0 && buf[i + 1] <= 0xBF) ||
                        (buf[i] == 0xED && buf[i + 1] >= 0x80 && buf[i + 1] <= 0x9F)
                    ) && buf[i + 2] >> 6 == 2
                ) {
                i += 3;

                continue;
            }

            // UTF8-3 = %xE1-EC 2( UTF8-tail )
            // UTF8-3 = %xEE-EF 2( UTF8-tail )
            if (
                    (
                        (buf[i] >= 0xE1 && buf[i] <= 0xEC) ||
                        (buf[i] >= 0xEE && buf[i] <= 0xEF)
                    ) &&
                    buf[i + 1] >> 6 == 2 &&
                    buf[i + 2] >> 6 == 2
            ) {
                i += 3;

                continue;                        
            }

            // UTF8-4 = %xF0 %x90-BF 2( UTF8-tail )
            //          %xF1-F3 3( UTF8-tail )
            //          %xF4 %x80-8F 2( UTF8-tail )
            if (
                    (
                        (buf[i] == 0xF0 && buf[i + 1] >= 0x90 && buf[i + 1] <= 0xBF) ||
                        (buf[i] >= 0xF1 && buf[i] <= 0xF3 && buf[i + 1] >> 6 == 2) ||
                        (buf[i] == 0xF4  && buf[i + 1] >= 0x80 && buf[i + 1] <= 0x8F)
                    ) &&
                buf[i + 2] >> 6 == 2 &&
                buf[i + 3] >> 6 == 2
            ) {
                i += 4;

                continue;
            }

            return false;
        }

        return true;
    }


    public static void main(String args[]) {
        int[] bytes = {0x20, 0xce, 0xd2, 0xca, 0xc7, 0xcb, 0xad, 0x0a};
        boolean result = App.isUTF8(bytes);

        System.out.println(result);
    }
}