Transformar uma String em MD5

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

public String convertMd5Passwd( String passwd ){
   try{
     MessageDigest md= MessageDigest.getInstance("MD5");
     md.update( passwd.getBytes() );
     BigInteger hash= new BigInteger(1, md.digest() );
     String passwordMd5= hash.toString(16);
     return passwordMd5;
   }catch(Exception e){
     e.printStackTrace();
     return null;
   }
}