/**

      * 将字节数组转换为字符串

      * 一个字节会形成两个字符，最终长度是原始数据的2倍

      * @param data

      * @return

      */

     public static String toHex(byte[] data){

         String ret = null;

         //TODO 将字节数组转换为字符串

         if (data != null && data.length>) {

             StringBuilder sb = new StringBuilder();

             for (byte b: data){

                 //分别获取高四位，低四位的内容，将两个数值，转为字符

                 int h = (b>>)&0x0f;

                 int l = b&0x0f;

                 char ch ,cl;

                 if( h >  ){

                     ch = (char) ('A'+(h-));

                 }else{  //0--9

                     ch = (char) (''+h);

                 }

                 if(l>){

                     cl = (char) ('A'+(l-));

                 }else{  //0--9

                     cl = (char) (''+l);

                 }

                     sb.append(ch).append(cl);

                 }

                   ret = sb.toString();

             }

         return ret;

     }

  public static byte[] fromHex(String str) {

         byte[] ret = null;

         //TODO 将Hex编码的字符串，还原为 原始的字节数组

         if (str != null) {

             int len = str.length();

             if (len >  && len %  == ) {

                 char[] chs = str.toCharArray();

                 ret = new byte[len / ];

                 for (int i = , j = ; i < len; i += , j++) {

                     char ch = chs[i];

                     char cl = chs[i + ];

                     int ih = , il = , v = ;

                     if (ch >= 'A' && ch <= 'F') {

                         ih =  + (ch - 'A');

                     } else if (ch >= 'a' && ch <= 'f') {

                         ih =  + (ch - 'a');

                     } else if (ch >= '' && ch <= '') {

                         ih = ch - '';

                     }

                     if (cl >= 'A' && cl <= 'F') {

                         il =  + (cl - 'A');

                     } else if (cl >= 'a' && cl <= 'f') {

                         il =  + (cl - 'a');

                     } else if (cl >= '' && cl <= '') {

                         il = cl - '';

                     }

                     v = ((ih & 0x0f) << ) | (il & 0x0f);

                     //赋值

                     ret[j] = (byte) v;

                 }

             }

         }

         return ret;

     }