JAVA IO - 生成文件的checksum值

import java.io.FileInputStream;
import java.security.MessageDigest;

public class CheckSumGenerator {
public static void main(String args[]) throws Exception {
String datafile = "C:\\work\\hello\\helloworld.txt";

MessageDigest md = MessageDigest.getInstance("MD5");
FileInputStream fis = new FileInputStream(datafile);
byte[] dataBytes = new byte[1024];

int nread = 0;

while ((nread = fis.read(dataBytes)) != -1) {
md.update(dataBytes, 0, nread);
}
;

byte[] mdbytes = md.digest();

// convert the byte to hex format
StringBuffer sb = new StringBuffer("");
for (int i = 0; i < mdbytes.length; i++) {
sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16)
.substring(1));
}

System.out.println("Digest(in hex format):: " + sb.toString());

}
}