Programming Jakarta Struts

Using ActionErrors

Earlier in this chapter, we saw that the validate( ) method returned an ActionErrors object. The ActionErrors class encapsulates one or more errors that have been discovered by the application. Each problem discovered is represented by an instance of org.apache.struts.action.ActionError.

An ActionErrors object has request scope. Once an instance is created and populated by the validate( ) method, it is stored into the request. Later, the JSP page can retrieve the object from the request and use the ActionError objects contained within it to display error messages to the user.

Tip

The Struts framework includes a JSP custom tag that makes retrieving and displaying the error messages very easy. This tag, called ErrorsTag, will be discussed in Chapter 8.

An instance of ActionErrors can be instantiated in the validate( ) method and populated by adding instances of the ActionError class to it. The LoginForm from Example 7-2 demonstrated this and is illustrated again here for convenience:

public ActionErrors validate(ActionMapping mapping, HttpServletRequest request){
  ActionErrors errors = new ActionErrors(  );

  if( getEmail() == null || getEmail().length(  ) < 1 ){
    errors.add("email", new ActionError("security.error.email.required"));
  }

  if( getPassword() == null || getPassword().length(  ) < 1 ){
    errors.add("password", new ActionError("security.error.password.required"));
  }
  return errors;
}

The validate( ) method in this fragment checks to make sure that the email and password ...