In the previous example you can see how to calculate the MD5 digest from a text or a string. We are using the Apache Commons Codec library and use the DigestUtils.md5Hex() method to generate the MD5. I’ve mention in that post that we can also generate the MD5 digest of a byte array and InputStream object. In the example below you’ll see an example to generate the MD5 digest of a text data stored in a file.

package org.kodejava.example.commons.codec;

import org.apache.commons.codec.digest.DigestUtils;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

public class MD5FileHashDemo {
    public static void main(String[] args) {
        try {
            // Define the data file path and create an InputStream object.
            String data = System.getProperty("user.dir") + "/target/classes/data.txt" ;
            File file = new File(data);
            InputStream is = new FileInputStream(file);

            // Calculates the MD5 digest of the given InputStream object.
            // It will generate a 32 characters hex string.
            String digest = DigestUtils.md5Hex(is);
            System.out.println("Digest = " + digest);
            System.out.println("Length = " + digest.length());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

The first thing we need to do is to add the import statement to our class to import the org.apache.commons.codec.digest.DigestUtils class. The DigestUtils.md5Hex() method define as a static method so that we don’t have to create an instance of DigestUtils class before we can use it. Before we create the InputStream object we define the path to our data file. I am creating the code snippet using Apache Maven as the build tools. That’s why you see my path the the data file is under the target/classes directory, because that directory is the default location where Maven will place the compiled classes and resource file. Next we create the File object from the defined path followed by creating the InputStream object of the File.

To generate the digest we can simply pass the instance of the InputStream object into the DigestUtils.md5Hex() method. And if there is no error occurred during the process we will get a 32 character of hex string as the output. One last thing that you have to do is the catch the possible exception thrown by the method. So we add the try-catch block and print the error stack trace to help us identify any error.

And here is the an example output generated by the code snippet above:

Digest = bafb2ec738d6de85170073c80a1008ad
Length = 32

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Wayan Saryada

Programmer, runner, recreational diver, currently living in the island of Bali, Indonesia. Mostly programming in Java, creating web based application with Spring Framework, Hibernate / JPA.

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