Simple base64-encoder for java

Base64.java

public class Base64
{
    public static String encode(byte[] data)
    {
        char[] tbl = {
            'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P',
            'Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f',
            'g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v',
            'w','x','y','z','0','1','2','3','4','5','6','7','8','9','+','/' };

        StringBuilder buffer = new StringBuilder();
        int pad = 0;
        for (int i = 0; i < data.length; i += 3) {

            int b = ((data[i] & 0xFF) << 16) & 0xFFFFFF;
            if (i + 1 < data.length) {
                b |= (data[i+1] & 0xFF) << 8;
            } else {
                pad++;
            }
            if (i + 2 < data.length) {
                b |= (data[i+2] & 0xFF);
            } else {
                pad++;
            }

            for (int j = 0; j < 4 - pad; j++) {
                int c = (b & 0xFC0000) >> 18;
                buffer.append(tbl[c]);
                b <<= 6;
            }
        }
        for (int j = 0; j < pad; j++) {
            buffer.append("=");
        }

        return buffer.toString();
    }

    public static byte[] decode(String data)
    {
        int[] tbl = {
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54,
            55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2,
            3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
            20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30,
            31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
            48, 49, 50, 51, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1 };
        byte[] bytes = data.getBytes();
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        for (int i = 0; i < bytes.length; ) {
            int b = 0;
            if (tbl[bytes[i]] != -1) {
                b = (tbl[bytes[i]] & 0xFF) << 18;
            }
            // skip unknown characters
            else {
                i++;
                continue;
            }

            int num = 0;
            if (i + 1 < bytes.length && tbl[bytes[i+1]] != -1) {
                b = b | ((tbl[bytes[i+1]] & 0xFF) << 12);
                num++;
            }
            if (i + 2 < bytes.length && tbl[bytes[i+2]] != -1) {
                b = b | ((tbl[bytes[i+2]] & 0xFF) << 6);
                num++;
            }
            if (i + 3 < bytes.length && tbl[bytes[i+3]] != -1) {
                b = b | (tbl[bytes[i+3]] & 0xFF);
                num++;
            }

            while (num > 0) {
                int c = (b & 0xFF0000) >> 16;
                buffer.write((char)c);
                b <<= 8;
                num--;
            }
            i += 4;
        }
        return buffer.toByteArray();
    }
}

Base64Test.java

import java.io.ByteArrayOutputStream;
import java.util.Random;
import java.util.Arrays;
import javax.xml.bind.DatatypeConverter;

public class Base64Test
{
    public static void print(byte[] bytes)
    {
        for (byte b : bytes) {
            System.out.printf("%02X ", b);
        }
        System.out.println();
    }

    public static void main(String[] args)
    {
        int steps = 1000000;
        Random rand = new Random(System.currentTimeMillis());

        System.out.println("Encode, decode");
        for (int count = 0; count < steps; count++) {
            int len = rand.nextInt(100)+1;
            byte[] original = new byte[len];
            for (int i = 0; i < len; i++) {
                original[i] = (byte)rand.nextInt(0xFF);
            }

            String encoded = Base64.encode(original);
            byte[] decoded = Base64.decode(encoded);

            if (!Arrays.equals(original, decoded)) {
                print(original);
                print(decoded);
                System.out.println();
            }
        }

        System.out.println("Encode, decode with other");
        for (int count = 0; count < steps; count++) {
            int len = rand.nextInt(100)+1;
            byte[] original = new byte[len];
            for (int i = 0; i < len; i++) {
                original[i] = (byte)rand.nextInt(0xFF);
            }

            String encoded = Base64.encode(original);
            byte[] decoded = DatatypeConverter.parseBase64Binary(encoded);

            if (!Arrays.equals(original, decoded)) {
                print(original);
                print(decoded);
                System.out.println();
            }
        }

        System.out.println("Encode with other, decode");
        for (int count = 0; count < steps; count++) {
            int len = rand.nextInt(100)+1;
            byte[] original = new byte[len];
            for (int i = 0; i < len; i++) {
                original[i] = (byte)rand.nextInt(0xFF);
            }

            String encoded = DatatypeConverter.printBase64Binary(original);
            byte[] decoded = Base64.decode(encoded);

            if (!Arrays.equals(original, decoded)) {
                print(original);
                print(decoded);
                System.out.println();
            }
        }

        System.out.println("Comparison test");
        for (int count = 0; count < 100000; count++) {
            int len = rand.nextInt(100)+1;
            byte[] original = new byte[len];
            for (int i = 0; i < len; i++) {
                original[i] = (byte)rand.nextInt(0xFF);
            }

            String encoded = DatatypeConverter.printBase64Binary(original);
            String encoded2 = Base64.encode(original);

            if (!encoded.equals(encoded2)) {
                System.out.println("mismatch");
                System.out.println(encoded);
                System.out.println(encoded2);
                System.out.println();
            }
        }
    }
}

gendecodetbl.py

# script to generate the reverse lookup table

s = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

res = [(ord(c), i) for i,c in enumerate(s)]

lookup = dict(res)

f = []
for i in xrange(0,255):
    if lookup.has_key(i):
        n = str(lookup[i])
        if len(n) == 1:
            n = " " + n
        f.append(" " + n)
    else:
        f.append(" " + str(-1))

print len(f)
print ",".join(f)

Kotlin Version https://gist.github.com/hrules6872/e2d4d02a1e8d3c6328ae5aeabc430b96

There are some bugs in decode method.

1. length of tbl array is 255. add one more.
2. java byte is signed value(-128 ~ 127). When invalid character is feeded, Exception occured. Some text editor add BOM character and it can cause that problem.

for (int i = 0; i < bytes.length;) {
   int b = 0;
   if (bytes[i] >= 0 && tbl[bytes[i]] != -1) {
      b = (tbl[bytes[i]] & 0xFF) << 18;
   }

@kimwooglae
May I ask you a question?
Why should the length of the tbl array be 256 instead of 255?