[转]Base64算法 java版

public class Base64
{
    private static final byte[]    encodingTable    = { (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F', (byte) 'G',
            (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P', (byte) 'Q',
            (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z', (byte) 'a',
            (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k',
            (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u',
            (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4',
            (byte) '5', (byte) '6', (byte) '7', (byte) '8', (byte) '9', (byte) '+', (byte) '/' };
    
    private static final byte[]    decodingTable;
    
    static
    {
        decodingTable = new byte[128];
        
        for (int i = 0; i < 128; i++)
        {
            decodingTable[i] = (byte) -1;
        }
        
        for (int i = 'A'; i <= 'Z'; i++)
        {
            decodingTable[i] = (byte) (i - 'A');
        }
        
        for (int i = 'a'; i <= 'z'; i++)
        {
            decodingTable[i] = (byte) (i - 'a' + 26);
        }
        
        for (int i = '0'; i <= '9'; i++)
        {
            decodingTable[i] = (byte) (i - '0' + 52);
        }
        
        decodingTable['+'] = 62;
        decodingTable['/'] = 63;
    }
    
    public static byte[] encode(byte[] data)
    {
        byte[] bytes;
        
        int modulus = data.length % 3;
        
        if (modulus == 0)
        {
            bytes = new byte[(4 * data.length) / 3];
        }
        else
        {
            bytes = new byte[4 * ((data.length / 3) + 1)];
        }
        
        int dataLength = (data.length - modulus);
        int a1;
        int a2;
        int a3;
        
        for (int i = 0, j = 0; i < dataLength; i += 3, j += 4)
        {
            a1 = data[i] & 0xff;
            a2 = data[i + 1] & 0xff;
            a3 = data[i + 2] & 0xff;
            
            bytes[j] = encodingTable[(a1 >>> 2) & 0x3f];
            bytes[j + 1] = encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f];
            bytes[j + 2] = encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f];
            bytes[j + 3] = encodingTable[a3 & 0x3f];
        }
        
        int b1;
        int b2;
        int b3;
        int d1;
        int d2;
        
        switch (modulus)
        {
            case 0: /* nothing left to do */
                break;
            
            case 1:
                d1 = data[data.length - 1] & 0xff;
                b1 = (d1 >>> 2) & 0x3f;
                b2 = (d1 << 4) & 0x3f;
                
                bytes[bytes.length - 4] = encodingTable[b1];
                bytes[bytes.length - 3] = encodingTable[b2];
                bytes[bytes.length - 2] = (byte) '=';
                bytes[bytes.length - 1] = (byte) '=';
                
                break;
            
            case 2:
                d1 = data[data.length - 2] & 0xff;
                d2 = data[data.length - 1] & 0xff;
                
                b1 = (d1 >>> 2) & 0x3f;
                b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f;
                b3 = (d2 << 2) & 0x3f;
                
                bytes[bytes.length - 4] = encodingTable[b1];
                bytes[bytes.length - 3] = encodingTable[b2];
                bytes[bytes.length - 2] = encodingTable[b3];
                bytes[bytes.length - 1] = (byte) '=';
                
                break;
        }
        
        return bytes;
    }
    
    public static byte[] decode(byte[] data)
    {
        byte[] bytes;
        byte b1;
        byte b2;
        byte b3;
        byte b4;
        
        data = discardNonBase64Bytes(data);
        
        if (data[data.length - 2] == '=')
        {
            bytes = new byte[(((data.length / 4) - 1) * 3) + 1];
        }
        else if (data[data.length - 1] == '=')
        {
            bytes = new byte[(((data.length / 4) - 1) * 3) + 2];
        }
        else
        {
            bytes = new byte[((data.length / 4) * 3)];
        }
        
        for (int i = 0, j = 0; i < (data.length - 4); i += 4, j += 3)
        {
            b1 = decodingTable[data[i]];
            b2 = decodingTable[data[i + 1]];
            b3 = decodingTable[data[i + 2]];
            b4 = decodingTable[data[i + 3]];
            
            bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));
            bytes[j + 2] = (byte) ((b3 << 6) | b4);
        }
        
        if (data[data.length - 2] == '=')
        {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];
            
            bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));
        }
        else if (data[data.length - 1] == '=')
        {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];
            b3 = decodingTable[data[data.length - 2]];
            
            bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));
        }
        else
        {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];
            b3 = decodingTable[data[data.length - 2]];
            b4 = decodingTable[data[data.length - 1]];
            
            bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));
            bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);
        }
        
        return bytes;
    }
    
    public static byte[] decode(String data)
    {
        byte[] bytes;
        byte b1;
        byte b2;
        byte b3;
        byte b4;
        
        data = discardNonBase64Chars(data);
        
        if (data.charAt(data.length() - 2) == '=')
        {
            bytes = new byte[(((data.length() / 4) - 1) * 3) + 1];
        }
        else if (data.charAt(data.length() - 1) == '=')
        {
            bytes = new byte[(((data.length() / 4) - 1) * 3) + 2];
        }
        else
        {
            bytes = new byte[((data.length() / 4) * 3)];
        }
        
        for (int i = 0, j = 0; i < (data.length() - 4); i += 4, j += 3)
        {
            b1 = decodingTable[data.charAt(i)];
            b2 = decodingTable[data.charAt(i + 1)];
            b3 = decodingTable[data.charAt(i + 2)];
            b4 = decodingTable[data.charAt(i + 3)];
            
            bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));
            bytes[j + 2] = (byte) ((b3 << 6) | b4);
        }
        
        if (data.charAt(data.length() - 2) == '=')
        {
            b1 = decodingTable[data.charAt(data.length() - 4)];
            b2 = decodingTable[data.charAt(data.length() - 3)];
            
            bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));
        }
        else if (data.charAt(data.length() - 1) == '=')
        {
            b1 = decodingTable[data.charAt(data.length() - 4)];
            b2 = decodingTable[data.charAt(data.length() - 3)];
            b3 = decodingTable[data.charAt(data.length() - 2)];
            
            bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));
        }
        else
        {
            b1 = decodingTable[data.charAt(data.length() - 4)];
            b2 = decodingTable[data.charAt(data.length() - 3)];
            b3 = decodingTable[data.charAt(data.length() - 2)];
            b4 = decodingTable[data.charAt(data.length() - 1)];
            
            bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));
            bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);
        }
        
        return bytes;
    }
    
    private static byte[] discardNonBase64Bytes(byte[] data)
    {
        byte[] temp = new byte[data.length];
        int bytesCopied = 0;
        
        for (int i = 0; i < data.length; i++)
        {
            if (isValidBase64Byte(data[i]))
            {
                temp[bytesCopied++] = data[i];
            }
        }
        
        byte[] newData = new byte[bytesCopied];
        
        System.arraycopy(temp, 0, newData, 0, bytesCopied);
        
        return newData;
    }
    
    private static String discardNonBase64Chars(String data)
    {
        StringBuffer sb = new StringBuffer();
        
        int length = data.length();
        
        for (int i = 0; i < length; i++)
        {
            if (isValidBase64Byte((byte) (data.charAt(i))))
            {
                sb.append(data.charAt(i));
            }
        }
        
        return sb.toString();
    }
    
    private static boolean isValidBase64Byte(byte b)
    {
        if (b == '=')
        {
            return true;
        }
        else if ((b < 0) || (b >= 128))
        {
            return false;
        }
        else if (decodingTable[b] == -1)
        {
            return false;
        }
        
        return true;
    }
    
    public static void main(String[] args)
    {
        String data = "1";
        byte[] result = Base64.encode(data.getBytes());
        System.out.println(data);
        System.out.println(new String(result));
        System.out.println(new String(Base64.decode(new String(result))));
    }
}