Java

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 MD5Util {    
		  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 md5Hex (String message) {         
		      try {             
			  MessageDigest md = 
			      MessageDigest.getInstance("MD5");             
			  return hex (md.digest(message.getBytes("CP1252")));         
		      } catch (NoSuchAlgorithmException e) {         
		      } catch (UnsupportedEncodingException e) {         
		      }         
		      return null;    
		  }    
		}
		

This class can then be used to return the MD5 hash of an email address like this:

String email = "someone@somewhere.com";
String hash = MD5Util.md5Hex(email);

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