DecodeBase64

package org.cnhawk.tools;
/*
 *Date Marth 19th,2007
 *
 **/

public class DecodeBase64 {

      //定义base64编码基本字符

       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', '+', '/' };

    //定义base64解码基本字符

       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 };

      

       public static void main(String args[]){

       String testStr="www.cnhawk.org";

       //编码测试

       String encodeStr=encode(testStr.getBytes());

      

       System.out.println("----------编码开始----------");

       System.out.println(encodeStr);

       System.out.println("----------编码结束----------");

      

       System.out.println("----------解码开始----------");

       try {

           System.out.println(new String(decode(encodeStr)));

       } catch (Exception e) {

           e.printStackTrace();

       }

       System.out.println("----------解码结束----------");

       }

 

       //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 Exception {

           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) {

               /* 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;

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

               /* b3 */

               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)));

               /* b4 */

               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");

      }

  }