关于BASE64，以及网上收集的各种编码解码实现

BASE64 编码是一种常用的字符编码，在很多地方都会用到。JDK 中提供了非常方便的 BASE64Encoder 和 BASE64Decoder，用它们可以非常方便的完成基于 BASE64 的编码和解码。下面是本人编的两个小的函数，分别用于 BASE64 的编码和解码：

// 将 s 进行 BASE64 编码
public static String getBASE64(String s) {
if (s == null) return null;
return (new sun.misc.BASE64Encoder()).encode( s.getBytes() );
}

// 将 BASE64 编码的字符串 s 进行解码
public static String getFromBASE64(String s) {
if (s == null) return null;
BASE64Decoder decoder = new BASE64Decoder();
try {
byte[] b = decoder.decodeBuffer(s);
return new String(b);
} catch (Exception e) {
return null;
}
}

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Base64加密算法源码

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 = "中华人民共和国";
        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))));
    }
}