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();
     }
 }