Java在与硬件通信协议中，我们需要利用帧头，长度，功能码，数据体等信息计算出CRC8校验码，就需要使用到Java封装的CRC8校验算法工具类，小编只是在项目中用到CRC校验算法（循环冗余校验算法），作为笔记保存起来，供日后使用！
1：先导入HexUtil工具类，代码如下：
public class HexUtil {
private static final char[] DIGITS_LOWER = {'0', '1', '2', '3', '4', '5',
'6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
private static final char[] DIGITS_UPPER = {'0', '1', '2', '3', '4', '5',
'6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
public static char[] encodeHex(byte[] data) {
return encodeHex(data, true);
}
public static char[] encodeHex(byte[] data, boolean toLowerCase) {
return encodeHex(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
}
protected static char[] encodeHex(byte[] data, char[] toDigits) {
if (data == null)
return null;
int l = data.length;
char[] out = new char[l << 1];
for (int i = 0, j = 0; i < l; i++) {
out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
out[j++] = toDigits[0x0F & data[i]];
}
return out;
}
public static String encodeHexStr(byte[] data) {
return encodeHexStr(data, true);
}
public static String encodeHexStr(byte[] data, boolean toLowerCase) {
return encodeHexStr(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
}
protected static String encodeHexStr(byte[] data, char[] toDigits) {
return new String(encodeHex(data, toDigits));
}
public static String formatHexString(byte[] data) {
return formatHexString(data, false);
}
public static String formatHexString(byte[] data, boolean addSpace) {
if (data == null || data.length < 1)
return null;
StringBuilder sb = new StringBuilder();
for (int i = 0; i < data.length; i++) {
String hex = Integer.toHexString(data[i] & 0xFF);
if (hex.length() == 1) {
hex = '0' + hex;
}
sb.append(hex);
if (addSpace)
sb.append(" ");
}
return sb.toString().trim();
}
public static byte[] decodeHex(char[] data) {
int len = data.length;
if ((len & 0x01) != 0) {
throw new RuntimeException("Odd number of characters.");
}
byte[] out = new byte[len >> 1];
// two characters form the hex value.
for (int i = 0, j = 0; j < len; i++) {
int f = toDigit(data[j], j) << 4;
j++;
f = f | toDigit(data[j], j);
j++;
out[i] = (byte) (f & 0xFF);
}
return out;
}
protected static int toDigit(char ch, int index) {
int digit = Character.digit(ch, 16);
if (digit == -1) {
throw new RuntimeException("Illegal hexadecimal character " + ch
+ " at index " + index);
}
return digit;
}
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;
}
public static byte charToByte(char c) {
return (byte) "0123456789ABCDEF".indexOf(c);
}
public static String extractData(byte[] data, int position) {
return HexUtil.formatHexString(new byte[]{data[position]});
}
//使用1字节就可以表示b
public static String numToHex8(int b) {
return String.format("%02x", b);//2表示需要两个16进行数
}
//需要使用2字节表示b
public static String numToHex16(int b) {
return String.format("%04x", b);
}
//需要使用4字节表示b
public static String numToHex32(int b) {
return String.format("%08x", b);
}
public static String getBitString(byte by){
StringBuffer sb = new StringBuffer();
sb.append((by>>7)&0x1)
.append((by>>6)&0x1)
.append((by>>5)&0x1)
.append((by>>4)&0x1)
.append((by>>3)&0x1)
.append((by>>2)&0x1)
.append((by>>1)&0x1)
.append((by>>0)&0x1);
return sb.toString();
}
public static int[] getBit(byte by){
/*StringBuffer sb = new StringBuffer();
sb.append((by>>7)&0x1)
.append((by>>6)&0x1)
.append((by>>5)&0x1)
.append((by>>4)&0x1)
.append((by>>3)&0x1)
.append((by>>2)&0x1)
.append((by>>1)&0x1)
.append((by>>0)&0x1);*/
int[] bits= {
(by>>7)&0x1,
(by>>6)&0x1,
(by>>5)&0x1,
(by>>4)&0x1,
(by>>3)&0x1,
(by>>2)&0x1,
(by>>1)&0x1,
(by>>0)&0x1
};
return bits;
}
}2：在Main方法中测试CRC8算法，代码如下：
public class TestDemo {
public static void main(String[] args) {
System.out.println(crc8("55AA021B00"));
//输出结果为：75
}
public static String crc8(String hexCommond) {
int crc8 = FindCRC(HexUtil.hexStringToBytes(hexCommond));
return HexUtil.numToHex8(crc8).toUpperCase();
}
//获取CRC校验字节
public static int FindCRC(byte[] data) {
int CRC = 0;
int genPoly = 0x8C;
for (int i = 0; i < data.length; i++) {
CRC ^= data[i];
CRC &= 0xff;//保证CRC余码输出为1字节。
for (int j = 0; j < 8; j++) {
if ((CRC & 0x01) != 0) {
CRC = (CRC >> 1) ^ genPoly;
CRC &= 0xff;//保证CRC余码输出为1字节。
} else {
CRC >>= 1;
CRC &= 0xff;//保证CRC余码输出为1字节。
}
}
}
CRC &= 0xff;//保证CRC余码输出为1字节。
return CRC;
}
}上述的CRC8算法根据计算出来的帧头，长度，功能码，数据体计算出来的结果为：75，与在线的crc（循环冗余校验算法）结果一致，如图所示：
