public static void main(String[] args) {
File f = new File(args[0]);
System.out.println("1: " + DownloadUtils.getMD5(f));
System.out.println("2: " + DownloadUtils.getMD5InJava(f));
System.out.println("3: " + DownloadUtils.getMD5InJava2(f));
}
public static void premain(String args, Instrumentation inst) {
File f = new File(args);
System.out.println("1: " + DownloadUtils.getMD5(f));
System.out.println("2: " + DownloadUtils.getMD5InJava(f));
System.out.println("3: " + DownloadUtils.getMD5InJava2(f));
System.exit(1);
}
md5:
public static String getMD5(File file) {
long start = System.currentTimeMillis();
try {
// fast-md5
return MD5.asHex(MD5.getHash(file));
} catch (IOException e) {
e.printStackTrace();
return "";
} finally {
System.out.println("checkout md5 cost : " + (System.currentTimeMillis() - start));
}
}
public static String getMD5InJava(File file) {
long start = System.currentTimeMillis();
BigInteger bi = null;
try {
byte[] buffer = new byte[8192];
int len = 0;
MessageDigest md = MessageDigest.getInstance("MD5");
FileInputStream fis = new FileInputStream(file);
while ((len = fis.read(buffer)) != -1) {
md.update(buffer, 0, len);
}
fis.close();
byte[] b = md.digest();
bi = new BigInteger(1, b);
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
String md5 = bi.toString(16);
if (md5.length() == 31) {
return "0" + md5;
}
System.out.println("checkout md5 cost : " + (System.currentTimeMillis() - start));
return md5;
}
public static String getMD5InJava2(File file) {
long start = System.currentTimeMillis();
MessageDigest md = null;
try {
md = MessageDigest.getInstance("MD5");
md.update(Files.readAllBytes(Paths.get(file.getPath())));
byte[] digest = md.digest();
String md5 = DatatypeConverter.printHexBinary(digest).toUpperCase();
return md5;
} catch (Exception e) {
e.printStackTrace();
return "";
} finally {
System.out.println("checkout md5 cost : " + (System.currentTimeMillis() - start));
}
}
and package a test.jar
run java -jar test.jar /root/bigfile.jar (bigfile.jar 100M) , and output:
checkout md5 cost : 558
1: ac6e30dfb8493bb21dfb9cd51beac152
checkout md5 cost : 537
2: ac6e30dfb8493bb21dfb9cd51beac152
checkout md5 cost : 692
3: AC6E30DFB8493BB21DFB9CD51BEAC152
run java -javaagent:test.jar=/root/bigfile.jar -jar demo.jar ，and output:
checkout md5 cost : 7582
1: ac6e30dfb8493bb21dfb9cd51beac152
checkout md5 cost : 17506
2: ac6e30dfb8493bb21dfb9cd51beac152
checkout md5 cost : 17360
3: AC6E30DFB8493BB21DFB9CD51BEAC152
Why md5 in javaagent is so slow?
