How to generate a SHA1 hash from a String in Java

05/09/2017

The SHA1 hash can be generated using DigestUtils from Apache commons.

Syntax:

	sha1 = org.apache.commons.codec.digest.DigestUtils.sha1Hex( value );

The SHA1 hash can also be generated directly using the MessageDigest class from the jdk:

Syntax:

	MessageDigest digest = MessageDigest.getInstance("SHA-1");
	digest.reset();
	digest.update(value.getBytes("utf8"));
	sha1 = String.format("%040x", new BigInteger(1, digest.digest()));

Here is an example creating the sha1 of the String "this is a test". First is uses the method using the MessageDigest class from the jdk. Then it uses the DigestUtils class from Apache commons. The generated sha1 are written in the console.

1- Create the following java file:

import java.math.BigInteger;
import java.security.MessageDigest;

public class SHA1 {

	public static void main(String[] argv){

		String value = "this is a test";

		String sha1 = "";
		
		// With the java libraries
		try {
			MessageDigest digest = MessageDigest.getInstance("SHA-1");
	        digest.reset();
	        digest.update(value.getBytes("utf8"));
	        sha1 = String.format("%040x", new BigInteger(1, digest.digest()));
		} catch (Exception e){
			e.printStackTrace();
		}

		System.out.println( "The sha1 of \""+ value + "\" is:");
		System.out.println( sha1 );
		System.out.println();

		// With Apache commons
		sha1 = org.apache.commons.codec.digest.DigestUtils.sha1Hex( value );

		System.out.println( "The sha1 of \""+ value + "\" is:");
		System.out.println( sha1 );

     }
}

The output will be:

The sha1 of "this is a test" is:
fa26be19de6bff93f70bc2308434e4a440bbad02

The sha1 of "this is a test" is:
fa26be19de6bff93f70bc2308434e4a440bbad02

References:

Java 8
Online tool generating SHA1
SHA1 Decoder

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