Base 编解码（转）

private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();

/** Base64 encode the given data */
    public static String encode(byte[] data) {
        int start = ;
        int len = data.length;
        StringBuffer buf = new StringBuffer(data.length *  / );

        int end = len - ;
        int i = start;
        int n = ;

        while (i <= end) {
            int d = ((((int) data[i]) & 0x0ff) << )
                    | ((((int) data[i + ]) & 0x0ff) << )
                    | (((int) data[i + ]) & 0x0ff);

            buf.append(legalChars[(d >> ) & ]);
            buf.append(legalChars[(d >> ) & ]);
            buf.append(legalChars[(d >> ) & ]);
            buf.append(legalChars[d & ]);

            i += ;

            if (n++ >= ) {
                n = ;
                buf.append("");
            }
        }

        if (i == start + len - ) {
            int d = ((((int) data[i]) & 0x0ff) << )
                    | ((((int) data[i + ]) & ) << );

            buf.append(legalChars[(d >> ) & ]);
            buf.append(legalChars[(d >> ) & ]);
            buf.append(legalChars[(d >> ) & ]);
            buf.append("=");
        } else if (i == start + len - ) {
            int d = (((int) data) & 0x0ff) << ;

            buf.append(legalChars[(d >> ) & ]);
            buf.append(legalChars[(d >> ) & ]);
            buf.append("==");
        }

        return buf.toString();
    }

    private static int decode(char c) {
        if (c >= 'A' && c <= 'Z')
            return ((int) c) - ;
        else if (c >= 'a' && c <= 'z')
            return ((int) c) -  + ;
        else if (c >= '' && c <= '')
            return ((int) c) -  +  + ;
        else
            switch (c) {
            case '+':
                return ;
            case '/':
                return ;
            case '=':
                return ;
            default:
                throw new RuntimeException("unexpected code: " + c);
            }
    }

    /**
     * Decodes the given Base64 encoded String to a new byte array. The byte
     * array holding the decoded data is returned.
     */

    public static byte[] decode(String s) {

        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        try {
            decode(s, bos);
        } catch (IOException e) {
            throw new RuntimeException();
        }
        byte[] decodedBytes = bos.toByteArray();
        try {
            bos.close();
            bos = null;
        } catch (IOException ex) {
            System.err.println("Error while decoding BASE64: " + ex.toString());
        }
        return decodedBytes;
    }

    private static void decode(String s, OutputStream os) throws IOException {
        int i = ;

        int len = s.length();

        while (true) {
            while (i < len && s.charAt(i) <= ' ')
                i++;

            if (i == len)
                break;

            int tri = (decode(s.charAt(i)) << )
                    + (decode(s.charAt(i + )) << )
                    + (decode(s.charAt(i + )) << )
                    + (decode(s.charAt(i + )));

            os.write((tri >> ) & );
            if (s.charAt(i + ) == '=')
                break;
            os.write((tri >> ) & );
            if (s.charAt(i + ) == '=')
                break;
            os.write(tri & );

            i += ;
        }
    }