public Boolean canExecute(String url){
  if (url.startsWith("http:") || url.startsWith("https:")) {
    return Boolean.TRUE;
  }
  return null;
}

public Boolean canExecute ( String url ) { if ( url . startsWith ( "http:" ) || url . startsWith ( "https:" ) ) { return Boolean . TRUE ; } return null ; }
returns true if executing this url should work , returns false if it will not and null if this is unknown .
