Java中String和byte[]互转问题

最近使用tlv协议传输数据，发现Java中的String存放二进制数剧是有问题的。代码如下：

byte[] bytes ={3,53,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,32,1,0,1,0,0,1,17,0,0,84,1,-128,97,97,97,97,97};
for(int i=0; i<40; ++i){
System.out.print(bytes[i] + ",");
}
System.out.println();

String str = new String(bytes, 0 , bytes.length, "UTF-8");
byte[] bytes_t = str.getBytes();//这个byte[]与之前的不相同
for(int i=0; i<40; ++i){
System.out.print(bytes_t[i] + ",");
}

输出结果为:

3,53,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,32,1,0,1,0,0,1,17,0,0,84,1,-128,97,97,97,97,97,

3,53,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,32,1,0,1,0,0,1,17,0,0,84,1,63,97,97,97,97,97,

可以看出用String构造函数生成的String，经过getBytes()函数后，得到的byte数组与之前的不一样。

所以当byte[]包含二进制数据时，不能用String构造函数将String转化为byte数组。

（如果是字符串经过getBytes()后得到的byte[]，这样互转是没有问题的）

正确的方法应该是把byte[]转化为16进制字符串；

然后再逆转化，就可以得到原来的byte[]。

byte[]和16进制字符串互转代码：

/**
* byte[]转化为16进制字符串
* @param src
* @return
*/
public static String bytesToHexString(byte[] src){
StringBuilder stringBuilder = new StringBuilder("");
if (src == null || src.length <= 0) {
return null;
}
for (int i = 0; i < src.length; i++) {
int v = src[i] & 0xFF;
String hv = Integer.toHexString(v);
if (hv.length() < 2) {
stringBuilder.append(0);
}
stringBuilder.append(hv);
}
return stringBuilder.toString();
}

/**
* 16进制字符串转化为byte[]
* @param hexString
* @return
*/
public static byte[] hexStringToBytes(String hexString) {
if (hexString == null || hexString.equals("")) {
return null;
}
hexString = hexString.toUpperCase();
int length = hexString.length() / 2;
char[] hexChars = hexString.toCharArray();
byte[] d = new byte[length];
for (int i = 0; i < length; i++) {
int pos = i * 2;
d[i] = (byte) (charToByte(hexChars[pos]) << 4 | charToByte(hexChars[pos + 1]));
}
return d;
}

private static byte charToByte(char c) {
return (byte) "0123456789ABCDEF".indexOf(c);
}

主函数调用：

String str_bin = bytesToHexString(bytes);
System.out.println(str_bin);

bytes = hexStringToBytes(str_bin);
for(int i=0; i<40; ++i){
System.out.print(bytes[i] + ",");
}

输出：

03350000000000000000000000000000000000000000200100010000011100005401806161616161

3,53,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,32,1,0,1,0,0,1,17,0,0,84,1,-128,97,97,97,97,97,

可以看出互转之后byte[]是没有问题的。