content: package com.rsa;
  
  import java.io.UnsupportedEncodingException;
  
  /**
   * 自定义Base64转换算法
   *
   * @author pengxiangxiang
   */
  public class Base64Helper {
      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};
  
      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) {
          try {
              return decodePrivate(str);
          } catch (UnsupportedEncodingException e) {
              // TODO Auto-generated catch block
              e.printStackTrace();
          }
          return new byte[]{};
      }
  
      private static byte[] decodePrivate(String str) throws UnsupportedEncodingException {
          StringBuffer sb = new StringBuffer();
          byte[] data = null;
          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("iso8859-1");
                  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("iso8859-1");
                  b4 = base64DecodeChars[b4];
              }
              while (i < len && b4 == -1);
              if (b4 == -1)
                  break;
              sb.append((char) (((b3 & 0x03) << 6) | b4));
          }
          return sb.toString().getBytes("iso8859-1");
      }
  
      public static void main(String[] args) throws UnsupportedEncodingException {
          String s = "abcd";
          System.out.println("加密前：" + s);
          String x = encode(s.getBytes());
          System.out.println("加密后：" + x);
          String x1 = new String(decode(x));
          System.out.println("解密后：" + x1);
      }
  }
  