Base64——API

public class Base64
{

    private static char alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=".toCharArray();
    private static byte codes[];

    public Base64()
    {
    }

    public static byte[] decode(char data[])
    {
        int tempLen = data.length;
        for (int ix = 0; ix < data.length; ix++)
            if (data[ix] > '\377' || codes[data[ix]] < 0)
                tempLen--;

        int len = (tempLen / 4) * 3;
        if (tempLen % 4 == 3)
            len += 2;
        if (tempLen % 4 == 2)
            len++;
        byte out[] = new byte[len];
        int shift = 0;
        int accum = 0;
        int index = 0;
        for (int ix = 0; ix < data.length; ix++)
        {
            int value = data[ix] <= '\377' ? ((int) (codes[data[ix]])) : -1;
            if (value >= 0)
            {
                accum <<= 6;
                shift += 6;
                accum |= value;
                if (shift >= 8)
                {
                    shift -= 8;
                    out[index++] = (byte)(accum >> shift & 0xff);
                }
            }
        }

        if (index != out.length)
            throw new Error("Miscalculated data length (wrote " + index + " instead of " + out.length + ")");
        else
            return out;
    }

    public static char[] encode(byte data[])
    {
        char out[] = new char[((data.length + 2) / 3) * 4];
        int i = 0;
        for (int index = 0; i < data.length; index += 4)
        {
            boolean quad = false;
            boolean trip = false;
            int val = 0xff & data[i];
            val <<= 8;
            if (i + 1 < data.length)
            {
                val |= 0xff & data[i + 1];
                trip = true;
            }
            val <<= 8;
            if (i + 2 < data.length)
            {
                val |= 0xff & data[i + 2];
                quad = true;
            }
            out[index + 3] = alphabet[quad ? val & 0x3f : 64];
            val >>= 6;
            out[index + 2] = alphabet[trip ? val & 0x3f : 64];
            val >>= 6;
            out[index + 1] = alphabet[val & 0x3f];
            val >>= 6;
            out[index] = alphabet[val & 0x3f];
            i += 3;
        }

        return out;
    }

    static
    {
        codes = new byte[256];
        for (int i = 0; i < 256; i++)
            codes[i] = -1;

        for (int i = 65; i <= 90; i++)
            codes[i] = (byte)(i - 65);

        for (int i = 97; i <= 122; i++)
            codes[i] = (byte)((26 + i) - 97);

        for (int i = 48; i <= 57; i++)
            codes[i] = (byte)((52 + i) - 48);

        codes[43] = 62;
        codes[47] = 63;
    }
}