[Java]字節數組互轉Hex編碼工具類

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.security.MessageDigest;
import java.util.Arrays;

public class HexCodeUtils {

    public static void main(String[] args) throws Exception {
        MessageDigest md = MessageDigest.getInstance("MD5");
        String str = "測試";
        byte[] digest = md.digest(str.getBytes());
        System.out.println(HexCodeUtils.toHexString(digest));
        //db06c78d1e24cf708a14ce81c9b617ec
        byte[] bytes = HexCodeUtils.decode("db06c78d1e24cf708a14ce81c9b617ec");
        System.out.println(Arrays.equals(digest, bytes));
    }

    private static final HexEncoder encoder = new HexEncoder();

    public static String toHexString(byte[] data) throws IOException {
        return toHexString(data, 0, data.length);
    }

    public static String toHexString(byte[] data, int off, int length) throws IOException {
        byte[] encoded = encode(data, off, length);
        return new String(encoded);
    }

    public static byte[] encode(byte[] data) throws IOException {
        return encode(data, 0, data.length);
    }

    public static byte[] encode(byte[] data, int off, int length) throws IOException {
        ByteArrayOutputStream bOut = new ByteArrayOutputStream();
        encoder.encode(data, off, length, bOut);
        return bOut.toByteArray();
    }

    public static int encode(byte[] data, OutputStream out) throws IOException {
        return encoder.encode(data, 0, data.length, out);
    }

    public static int encode(byte[] data, int off, int length, OutputStream out) throws IOException {
        return encoder.encode(data, off, length, out);
    }

    public static byte[] decode(byte[] data) throws IOException {
        ByteArrayOutputStream bOut = new ByteArrayOutputStream();
        encoder.decode(data, 0, data.length, bOut);
        return bOut.toByteArray();
    }

    public static byte[] decode(String data) throws IOException {
        ByteArrayOutputStream bOut = new ByteArrayOutputStream();
        encoder.decode(data, bOut);
        return bOut.toByteArray();
    }

    public static int decode(String data, OutputStream out) throws IOException {
        return encoder.decode(data, out);
    }
}

class HexEncoder {
    private final byte[] encodingTable = {
            (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7',
            (byte) '8', (byte) '9', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f'
    };

    private final byte[] decodingTable = new byte[128];

    private void initialiseDecodingTable() {
        for ( int i = 0; i < decodingTable.length; i++ ) {
            decodingTable[i] = (byte) 0xff;
        }

        for ( int i = 0; i < encodingTable.length; i++ ) {
            decodingTable[encodingTable[i]] = (byte) i;
        }

        decodingTable['A'] = decodingTable['a'];
        decodingTable['B'] = decodingTable['b'];
        decodingTable['C'] = decodingTable['c'];
        decodingTable['D'] = decodingTable['d'];
        decodingTable['E'] = decodingTable['e'];
        decodingTable['F'] = decodingTable['f'];
    }

    public HexEncoder() {
        initialiseDecodingTable();
    }

    private static boolean ignore(char c) {
        return c == '\n' || c == '\r' || c == '\t' || c == ' ';
    }

    public int encode(byte[] data, int off, int length, OutputStream out) throws IOException {
        for ( int i = off; i < (off + length); i++ ) {
            int v = data[i] & 0xff;
            out.write(encodingTable[(v >>> 4)]);
            out.write(encodingTable[v & 0xf]);
        }
        return length * 2;
    }

    public int decode(byte[] data, int off, int length, OutputStream out) throws IOException {
        byte b1, b2;
        int outLen = 0;
        int end = off + length;

        while ( end > off ) {
            if ( !ignore((char) data[end - 1]) ) break;
            end--;
        }

        int i = off;
        while ( i < end ) {
            while ( i < end && ignore((char) data[i]) ) i++;
            b1 = decodingTable[data[i++]];

            while ( i < end && ignore((char) data[i]) ) i++;
            b2 = decodingTable[data[i++]];

            if ( (b1 | b2) < 0 ) throw new IOException("invalid characters encountered in Hex data");
            out.write((b1 << 4) | b2);
            outLen++;
        }
        return outLen;
    }

    public int decode(String data, OutputStream out) throws IOException {
        byte b1, b2;
        int length = 0;

        int end = data.length();
        while ( end > 0 ) {
            if ( !ignore(data.charAt(end - 1)) ) break;
            end--;
        }

        int i = 0;
        while ( i < end ) {
            while ( i < end && ignore(data.charAt(i)) ) i++;
            b1 = decodingTable[data.charAt(i++)];

            while ( i < end && ignore(data.charAt(i)) ) i++;
            b2 = decodingTable[data.charAt(i++)];

            if ( (b1 | b2) < 0 ) throw new IOException("invalid characters encountered in Hex string");
            out.write((b1 << 4) | b2);
            length++;
        }
        return length;
    }
}

來源：www.bouncycastle.org