Question

I am using Spring MVC to build my web application, and I have a question about validating parameters I receive in the URL. What is the best way to detect invalid parameters and display errors to the user?

Suppose I have a ‘View User Profile’ page. The profile that is displayed is based on a user ID parameter specified in the URL. I might go to the following address to view the profile of the user with ID 92:

http://www.somedomain.com/profile.html?id=92

I have created a ProfileControlller object which will do the following:

1. Get the id parameter from the request object
2. Load a UserProfile object from my database
3. Add the UserProfile object to the model
4. Construct a ModelAndView with my model and the ‘View User Profile’ JSP

That works fine if the user enters a valid ID number. My UserProfile object is loaded and displayed perfectly using JSP. But what if someone passes user ID -30294 to my page? My data access layer will simply return a null object if the ID is invalid, but I would like to show a friendly error message to the user. Is checking for a null UserProfile object in the JSP code really the best solution here?

Since I am new to Spring, I’m not sure. I like the way Validator classes can be used with FormController objects, if that is any help.

Answer 1

If the DAO returns null, simply return a ModelAndView for an error page.

Example:

UserProfile profile = userProfileDao.findUserProfileById(userId); if (profile == null) {     return new ModelAndView('Error', 'message', 'Invalid user ID'); } else {     // process accordingly. } 

In the Spring 2.5 distribution, check the jpetstore application in the samples directory. Find the org.springframework.samples.jpetstore.web.spring.SignonController for a simple example with an application.