In this example we shall show you how to check message consistency using hash functions. We are using the java.security.MessageDigest Class, that provides the functionality of a message digest algorithm. It takes arbitrary-sized data and outputs a fixed-length hash value. To check the consistency of two messages using the MessageDigest hash function, one should perform the following steps:

• Create a MessageDigest Object that implements the “MD5” algorithm.
• Update the digest with the byte array from a given String, using the update(byte[] input) API method.
• Complete the hash computation, using the digest API method and return the computated hash value in a byte array.
• Invoke the above steps for two different Strings, as shown in the getDigest(String str) method of the example, and then use the isEqual(byte[] digesta, byte[] digestb) API method to compare the two results, in order to check their consistency.

Let’s take a look at the code snippet that follows:

package com.javacodegeeks.snippets.core;

import java.security.MessageDigest;

public class Main {

    public static void main(String[] args) throws Exception {


  String str1 = "javacodegeeks.com";

  String str2 = "javacodegeeks";

  byte[] fDigest = getDigest(str1);

  byte[] sDigest = getDigest(str2);


  if (MessageDigest.isEqual(fDigest, sDigest)) {


System.out.println("str1 is equal to str2");

  } else {


System.out.println("str1 is NOT equal to str2");

  }
    }

    public static byte[] getDigest(String str) throws Exception {

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

  byte[] data = str.getBytes();

 

  hash.update(data);


  return hash.digest();
    }
}

Output:

str1 is NOT equal to str2

 
This was an example of how to check message consistency using the MessageDigest hash function in Java.