MD5 checksums are good to verify integrity of files and It's easy to
generate MD5 checksum in Java. Java provides couple of ways to generate MD5
checksum for any file, you can either use java.security.MessageDigest or any
open source library like Apache commons codec or Spring. All 3 ways we have
seen in our earlier article about generating MD5 hash for String
is also applicable to generate MD5
checksum for any file. Since most of md5() or md5Hex() method
takes byte[], you can simply read bytes from InputStream or pass to
these md5 methods. Apache commons codec from version 1.4 also provides an overloaded
method to accept InputStream, which makes
generating checksum very easy in Java. For those who are not familiar with
checksum, it's a fixed size datum generated from a block of data to detect any
accidental change in data. Which means once you create checksum for a file,
which is based on contents of file, any change on file e.g. adding white space,
deleting a character will result in different checksum. By comparing stored
checksum with current checksum, you can detect any change on File. It's good
practice to provide checksum of WAR or JAR files to support teams for
production release. In this Java tutorial we will learn how to create MD5
checksum for any file in Java.
Java program to generate MD5 checksum for
Files
When we create MD5 checksum for a File any further change's produce adifferent checksum. In this Java program we will see two ways to create MD5
checksum for a File. In first method we have used standard Java library and
MessageDigest from security package to create MD5 checksum. If you notice we
have used update() method of MessageDigest, instead
calling digest with a byte[]. This is a right way to generate
MD5 checksum of a File because Fie could be very large and you might not have
enough memory to read entire file as byte array and result in Java.lang.OutOfMemoryError: Java Heap
Space. It's better to read data in parts and update MessageDigest. Second
method uses Apache commons Codec to generate MD5 checksum of a File. DigestUtils provides
overloaded method md5Hex() which can accept InputStream from
version 1.4, which means you don't need to convert InputStream to String or
byte array. Let's see complete Java example to create MD5 checksum for any file
in Java.
import
java.io.FileInputStream;
import
java.io.IOException;
import
java.math.BigInteger;
import
java.security.MessageDigest;
import
java.security.NoSuchAlgorithmException;
import
java.util.logging.Level;
import
java.util.logging.Logger;
import
org.apache.commons.codec.digest.DigestUtils;
/**
* Java program to generate MD5 checksum for
files in Java. This Java example
* uses core Java security package and Apache
commons codec to generate MD5
* checksum for a File.
*
* @author Javin Paul
*/
public class MD5Checksum {
private static final Logger logger = Logger.getLogger(MD5Checksum.class.getName());
public static void main(String args[]) {
String file = "C:/temp/abc.txt";
System.out.println("MD5
checksum for file using Java : "
+ checkSum(file));
System.out.println("MD5
checksum of file in Java using Apache commons codec: "
+
checkSumApacheCommons(file));
}
/*
* Calculate checksum of a File using MD5
algorithm
*/
public static String checkSum(String path){
String checksum = null;
try {
FileInputStream fis = new
FileInputStream(path);
MessageDigest md = MessageDigest.getInstance("MD5");
//Using MessageDigest update() method
to provide input
byte[] buffer = new byte[8192];
int numOfBytesRead;
while( (numOfBytesRead
= fis.read(buffer)) > 0){
md.update(buffer, 0,
numOfBytesRead);
}
byte[] hash = md.digest();
checksum = new BigInteger(1, hash).toString(16); //don't use
this, truncates leading zero
} catch (IOException ex)
{
logger.log(Level.SEVERE, null, ex);
} catch
(NoSuchAlgorithmException ex) {
logger.log(Level.SEVERE, null, ex);
}
return checksum;
}
/*
* From Apache commons codec 1.4 md5() and
md5Hex() method accepts InputStream as well.
* If you are using lower version of Apache
commons codec than you need to convert
* InputStream to byte array before passing
it to md5() or md5Hex() method.
*/
public static String checkSumApacheCommons(String file){
String checksum = null;
try {
checksum = DigestUtils.md5Hex(new
FileInputStream(file));
} catch (IOException ex)
{
logger.log(Level.SEVERE, null, ex);
}
return checksum;
}
}
Output:
MD5 checksum for file using Java : cf4ab086129e7b3fe98881df2b526db4
MD5 checksum of file
in Java using Apache commons codec:
cf4ab086129e7b3fe98881df2b526db4
Some programmer uses BigInteger to convert
byte array to Hex String, as shown above, may be because its looks a beautiful
one liner But it truncates leading zero, which can cause some problems. Let's
run this program again with by changing file's content to 27, which produces
MD5 checksum with leading zero.
MD5 checksum for file using
Java : 2e74f10e0327ad868d138f2b4fdd6f0
MD5 checksum of file in Java
using Apache commons codec:
02e74f10e0327ad868d138f2b4fdd6f0
Now you can see output from first method to create MD5 checksum only
contains 31 characters and leading zero is missing. It's better to use conventional way to convert byte array to
Hex String rather that using this shortcut. If you really like using
BigInteger, than you make up for those leading zero by using
format method of String. You can take advantage of fact that BigInteger only
truncates leading zero and String always contains 32 characters. Here is a way
to use format method of String to produce 32 char, lowercase, hexadecimal
String which is left padded with 0 :
String.format("%032x",new BigInteger(1,
hash));
if you replace toString() method of BigInteger with format method of String, you
will receive same output from both methods.
That's all on How to generate MD5 checksum for a File in Java. As
I said it's good to verify checksum of Files before releasing it to production
environment and It's pretty easy to generate MD5 checksum in Java using Apache
Commons Codec or even Spring.
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