Base64正反编码

public class Base64 {  
    private static char[] base64EncodeChars = new char[] {  
        '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', '+', '/' };  
   
    private static byte[] base64DecodeChars = new byte[] {  
    -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 };  
   
    Base64() {}  
   
    public static String encode(byte[] data) {  
        StringBuffer sb = new StringBuffer();  
        int len = data.length;  
        int i = 0;  
        int b1, b2, b3;  
   
        while (i < len) {  
            b1 = data[i++] & 0xff;  
            if (i == len) {  
                sb.append(base64EncodeChars[b1 >>> 2]);  
                sb.append(base64EncodeChars[(b1 & 0x3) << 4]);  
                sb.append("==");  
                break;  
            }  
            b2 = data[i++] & 0xff;  
            if (i == len) {  
                sb.append(base64EncodeChars[b1 >>> 2]);  
                sb.append(  
                        base64EncodeChars[((b1 & 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);  
                sb.append(base64EncodeChars[(b2 & 0x0f) << 2]);  
                sb.append("=");  
                break;  
            }  
            b3 = data[i++] & 0xff;  
            sb.append(base64EncodeChars[b1 >>> 2]);  
            sb.append(  
                    base64EncodeChars[((b1 & 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);  
            sb.append(  
                    base64EncodeChars[((b2 & 0x0f) << 2) | ((b3 & 0xc0) >>> 6)]);  
            sb.append(base64EncodeChars[b3 & 0x3f]);  
        }  
        return sb.toString();  
    }  
   
    public static byte[] decode(String str) {  
        byte[] data = str.getBytes();  
        int len = data.length;  
        ByteArrayOutputStream buf = new ByteArrayOutputStream(len);  
        int i = 0;  
        int b1, b2, b3, b4;  
   
        while (i < len) {  
   
            /* b1 */  
            do {  
                b1 = base64DecodeChars[data[i++]];  
            } while (i < len && b1 == -1);  
            if (b1 == -1) {  
                break;  
            }  
   
            /* b2 */  
            do {  
                b2 = base64DecodeChars[data[i++]];  
            } while (i < len && b2 == -1);  
            if (b2 == -1) {  
                break;  
            }  
            buf.write((int) ((b1 << 2) | ((b2 & 0x30) >>> 4)));  
   
            /* b3 */  
            do {  
                b3 = data[i++];  
                if (b3 == 61) {  
                    return buf.toByteArray();  
                }  
                b3 = base64DecodeChars[b3];  
            } while (i < len && b3 == -1);  
            if (b3 == -1) {  
                break;  
            }  
            buf.write((int) (((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));  
   
            /* b4 */  
            do {  
                b4 = data[i++];  
                if (b4 == 61) {  
                    return buf.toByteArray();  
                }  
                b4 = base64DecodeChars[b4];  
            } while (i < len && b4 == -1);  
            if (b4 == -1) {  
                break;  
            }  
            buf.write((int) (((b3 & 0x03) << 6) | b4));  
        }  
        return buf.toByteArray();  
    }  
}