扩展Base64编码

import java.lang.*;

import java.io.*;

public class CLSBase64 {

     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 };

     //编码

     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();

     }

     //解码

     public static byte[] decode(String str) throws UnsupportedEncodingException {

         StringBuffer sb = new StringBuffer();

         byte[] data = str.getBytes("US-ASCII");

         int len = data.length;

         int i = 0;

         int b1, b2, b3, b4;

         while (i < len) {

             do {

                 b1 = base64DecodeChars[data[i++]];

             } while (i < len && b1 == -1);

             if (b1 == -1) break;

             do {

                 b2 = base64DecodeChars[data[i++]];

             } while (i < len && b2 == -1);

             if (b2 == -1) break;

             sb.append((char)((b1 << 2) | ((b2 & 0x30) >>> 4)));

             do {

                 b3 = data[i++];

                 if (b3 == 61) return sb.toString().getBytes("ISO-8859-1");

                 b3 = base64DecodeChars[b3];

             } while (i < len && b3 == -1);

             if (b3 == -1) break;

             sb.append((char)(((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));

             do {

                 b4 = data[i++];

                 if (b4 == 61) return sb.toString().getBytes("ISO-8859-1");

                 b4 = base64DecodeChars[b4];

             } while (i < len && b4 == -1);

             if (b4 == -1) break;

             sb.append((char)(((b3 & 0x03) << 6) | b4));

         }

         return sb.toString().getBytes("ISO-8859-1");

     }

 }