How to generate a file checksum value in Java

Here is a simple example to demonstrate how to generate a file checksum value in Java (SHA-1).

import java.io.FileInputStream;
import java.security.MessageDigest;
 
public class TestCheckSum {
 
  public static void main(String args[]) throws Exception {
 
    String datafile = "c:\\INSTLOG.TXT";
 
    MessageDigest md = MessageDigest.getInstance("SHA1");
    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());
 
  }
}

Result

Digest(in hex format):: bf35fa420d3e0f669e27b337062bf19f510480d4

The “INSTLOG.TXT” file has a “bf35fa420d3e0f669e27b337062bf19f510480d4″ SHA-1 checksum value. If we want to generate a Checksum value in MD5 format , we can change the MessageDigest as following

MessageDigest md = MessageDigest.getInstance("MD5");

More detail about Message Digest Algorithms, please check following website
http://java.sun.com/j2se/1.4.2/docs/guide/security/CryptoSpec.html#AppA

Reference

1) http://www.itl.nist.gov/fipspubs/fip180-1.htm
2) http://java.sun.com/j2se/1.4.2/docs/api/java/security/MessageDigest.html
3) http://java.sun.com/j2se/1.4.2/docs/guide/security/CryptoSpec.html

anon says:

October 7, 2009 at 10:23 am

Why are you adding 0×100?
If you simple use Integer.toString((byte & 0xFF), 16) you would get the same result.

mkyong says:

October 7, 2009 at 3:20 pm

hi anon, thanks for the tips ~

Interesting says:

October 7, 2009 at 10:19 am

Interesting approach, how does it compare to using the CheckedInputStream?

mkyong says:

October 7, 2009 at 3:21 pm

i never use CheckedInputStream before, would you mind to share your experience ?

- Interesting says:
  
  October 8, 2009 at 1:06 am
  
  It works well: javadoc
  Example (identical to readying any stream):
  try { // Compute Adler-32 checksum CheckedInputStream cis = new CheckedInputStream(new FileInputStream("filename"), new Adler32()); byte[] tempBuf = new byte[128]; while (cis.read(tempBuf) >= 0){} long checksum = cis.getChecksum().getValue(); } catch (IOException e) { }

Charlie Hayes says:

October 6, 2009 at 4:33 am

You might consider using Adler32 instead of SHA1. It’s a whole lot faster. That is of-course unless you are using the checksum as some sort of identifier for the file, in which case the size of SHA1’s hash might be helpful.

http://java.sun.com/j2se/1.4.2/docs/api/java/util/zip/Adler32.html
http://www.anomalousanomaly.com/docs/CheckMark%20Results.pdf

mkyong says:

October 6, 2009 at 10:43 am

Thanks for the suggestion and links provided. I always SHA-1 to generate the checksum value for the file, will look into the Adler32~