Create a checksum : Digest Stream « Security « Java Tutorial

1. Java Tutorial
2. Security
3. Digest Stream

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

public class Main {
  public static void main(String args[]) throws Exception {
    InputStream fis = new FileInputStream("a.exe");

    byte[] buffer = new byte[1024];
    MessageDigest complete = MessageDigest.getInstance("MD5");
    int numRead;
    do {
      numRead = fis.read(buffer);
      if (numRead > 0) {
        complete.update(buffer, 0, numRead);
      }
    } while (numRead != -1);
    fis.close();
    
    byte[] b = complete.digest();
    String result = "";
    for (int i = 0; i < b.length; i++) {
      result += Integer.toString((b[i] & 0xff) + 0x100, 16).substring(1);
    }
    System.out.println(result);

  }
}