Java – Gravatar Developer Docs

If you’d like an easy way of working with Gravatar, then check out Ralf Ebert’s jgravatar library, otherwise read on. Things are a little complex in Java. The following class will provide you with a static method that returns the hex format md5 of an input string:

import java.util.*;
import java.io.*;
import java.security.*;

public class HashUtil {
    public static String hex(byte[] array) {
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < array.length; ++i) {
            sb.append(Integer.toHexString((array[i]
                & 0xFF) | 0x100).substring(1,3));        
        }
        return sb.toString();
    }

    public static String sha256Hex(String message) {
        try {
            MessageDigest md = MessageDigest.getInstance("SHA-256");
            return hex(md.digest(message.getBytes("UTF-8")));
        } catch (NoSuchAlgorithmException e) {
            // Consider logging this exception or rethrowing as a RuntimeException
        } catch (UnsupportedEncodingException e) {
            // Consider logging this exception or rethrowing as a RuntimeException
        }
        return null;
    }
}

This class can then be used to return the MD5 hash of an email address (make sure you lower case it first!) like this:

String email = "someone@somewhere.com".toLowerCase();
String hash = sha256Hex(email);
String gravatarURL = "https://gravatar.com/avatar/" + hash;

With the hex string that is returned, you can construct your gravatar URL.