Base64工具類

public final class AbBase64 {
    
    /** The Constant base64EncodeChars. */
    private static final 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', '+', '/'};
    
    /** The Constant base64DecodeChars. */
    private static final 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};
    
    /**
     * Encode.
     *
     * @param str the str
     * @param charsetName the charset name
     * @return the string
     */
    public static final String encode(String str, String charsetName) {
        return encode(str, charsetName, 0);
    }
    
    /**
     * Encode.
     *
     * @param str the str
     * @param charsetName the charset name
     * @param width the width
     * @return the string
     */
    public static final String encode(String str, String charsetName, int width) {
        byte[] data = null;
        try {
            data = str.getBytes(charsetName);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            return null;
        }
        int length = data.length;
        int size = (int) Math.ceil(length * 1.36);
        int splitsize = width > 0 ? size / width : 0;
        StringBuffer sb = new StringBuffer(size + splitsize);
        int r = length % 3;
        int len = length - r;
        int i = 0;
        int c;
        while (i < len) {
            c = (0x000000ff & data[i++]) << 16 | (0x000000ff & data[i++]) << 8 | (0x000000ff & data[i++]);
            sb.append(base64EncodeChars[c >> 18]);
            sb.append(base64EncodeChars[c >> 12 & 0x3f]);
            sb.append(base64EncodeChars[c >> 6 & 0x3f]);
            sb.append(base64EncodeChars[c & 0x3f]);
        }
        if (r == 1) {
            c = 0x000000ff & data[i++];
            sb.append(base64EncodeChars[c >> 2]);
            sb.append(base64EncodeChars[(c & 0x03) << 4]);
            sb.append("==");
        } else if (r == 2) {
            c = (0x000000ff & data[i++]) << 8 | (0x000000ff & data[i++]);
            sb.append(base64EncodeChars[c >> 10]);
            sb.append(base64EncodeChars[c >> 4 & 0x3f]);
            sb.append(base64EncodeChars[(c & 0x0f) << 2]);
            sb.append("=");
        }
        if (splitsize > 0) {
            char split = '\n';
            for (i = width; i < sb.length(); i++) {
                sb.insert(i, split);
                i += width;
            }
        }
        return sb.toString();
    }
    
    /**
     * Decode.
     *
     * @param str the str
     * @param charsetName the charset name
     * @return the string
     */
    public static final String decode(String str, String charsetName) {
        byte[] data = null;
        try {
            data = str.getBytes(charsetName);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            return null;
        }
        int len = data.length;
        ByteArrayOutputStream buf = new ByteArrayOutputStream((int) (len * 0.67));
        int i = 0;
        int b1, b2, b3, b4;
        while (i < len) {
            do {
                if (i >= len) {
                    b1 = -1;
                    break;
                }
                b1 = base64DecodeChars[data[i++]];
            } while (i < len && b1 == -1);
            if (b1 == -1) {
                break;
            }
            do {
                if (i >= len) {
                    b2 = -1;
                    break;
                }
                b2 = base64DecodeChars[data[i++]];
            } while (i < len && b2 == -1);
            if (b2 == -1) {
                break;
            }
            buf.write((int) ((b1 << 2) | ((b2 & 0x30) >>> 4)));
            do {
                if (i >= len) {
                    b3 = -1;
                    break;
                }
                b3 = data[i++];
                if (b3 == 61) {
                    b3 = -1;
                    break;
                }
                b3 = base64DecodeChars[b3];
            } while (i < len && b3 == -1);
            if (b3 == -1) {
                break;
            }
            buf.write((int) (((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));
            do {
                if (i >= len) {
                    b4 = -1;
                    break;
                }
                b4 = data[i++];
                if (b4 == 61) {
                    b4 = -1;
                    break;
                }
                b4 = base64DecodeChars[b4];
            } while (b4 == -1);
            if (b4 == -1) {
                break;
            }
            buf.write((int) (((b3 & 0x03) << 6) | b4));
        }
        try {
            return buf.toString(charsetName);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            return null;
        }
    }
}

author 還如一夢中