Hex编码字节

/**
* 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>0) {
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>>4)&0x0f;
int l = b&0x0f;
char ch ,cl;
if( h > 9 ){
ch = (char) ('A'+(h-10));
}else{  //0--9
ch = (char) ('0'+h);
}

if(l>9){
cl = (char) ('A'+(l-10));
}else{  //0--9
cl = (char) ('0'+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 > 0 && len % 2 == 0) {
char[] chs = str.toCharArray();
ret = new byte[len / 2];
for (int i = 0, j = 0; i < len; i += 2, j++) {
char ch = chs[i];
char cl = chs[i + 1];

int ih = 0, il = 0, v = 0;
if (ch >= 'A' && ch <= 'F') {
ih = 10 + (ch - 'A');
} else if (ch >= 'a' && ch <= 'f') {
ih = 10 + (ch - 'a');
} else if (ch >= '0' && ch <= '9') {
ih = ch - '0';
}

if (cl >= 'A' && cl <= 'F') {
il = 10 + (cl - 'A');
} else if (cl >= 'a' && cl <= 'f') {
il = 10 + (cl - 'a');
} else if (cl >= '0' && cl <= '9') {
il = cl - '0';
}

v = ((ih & 0x0f) << 4) | (il & 0x0f);
//赋值
ret[j] = (byte) v;
}
}
}
return ret;
}