Spring MVC - command object binding question

Question

I'm using a domain object as a command object in the web layer. In one case, this command object is backing a form that represents a partial update of the domain object.

@RequestMapping( value = "/club/edit", method = RequestMethod.GET )
public String setupEditClubForm( ModelMap model, @RequestParam( "clubId" ) Long clubId ) {
    Club club = clubService.findClubById( clubId );
    model.addAttribute( "club", club );
    model.addAttribute( "action", "edit" );
    return "clubForm";
}

@RequestMapping( value = "/club/edit", method = RequestMethod.POST )
public String processEditClubForm( ClubEntity club, BindingResult result ) {
    if ( result.hasErrors() ) {
        return "clubForm";
    }
    clubService.updateClub( club );
    return "redirect:/club/" + club.getId();
}

My problem is that the domain object has some fields that are not changed by submitting this form. These fields that don't have the corresponding request parameters become null, I need them to stay as they are.

I though that this could be fixed by putting the object in the session (via @SessionAttributes) to allow it to live between the two requests, but it doesn't work.

I looked in the Spring reference, but I couldn't find any information on how Spring manipulates the command objects.

is there any reason one is a club and one is a clubentity? maybe try using the same interface for both. — Daniel Alexiuc
– Daniel Alexiuc, Commented Oct 18, 2010 at 2:58
Good point! I'm not sure why I used the ClubEntity type in the second method, but when I changed it to the interface type Club, Spring complained about being unable to instantiate an interface and I realized my mistake! I'm actually creating a new command object in the processEditClubForm method! Thanks for pointing this out! — brabec
– brabec, Commented Oct 18, 2010 at 7:05
Just a note on your @RequestParam( "clubId" ) Long clubId. You may want to have the type be String then do a Long.parseLong(blah) in your code so you catch any NumberFormatExceptions — DwB
– DwB, Commented Oct 18, 2010 at 14:28
dwb: That's a very good advice, thanks! I haven't thought of that. — brabec
– brabec, Commented Oct 19, 2010 at 15:03
Sorry, I was curious. What did the problem turn out to be (for the question you just deleted)? — user1726343
– user1726343, Commented Apr 22, 2013 at 19:40

brabec · Accepted Answer · 2010-10-18 07:09:39Z

2

Well, the problem was simple - I was actually creating a new command object in the processEditClubForm method. Here is the correct method code:

@RequestMapping( value = "/club/edit", method = RequestMethod.POST )
public String processEditClubForm( @ModelAttribute Club club, BindingResult result ) {
    if ( result.hasErrors() ) {
        return "clubForm";
    }
    clubService.updateClub( club );
    return "redirect:/club/" + club.getId();
}

Thanks to Daniel for making me see it :-)

answered Oct 18, 2010 at 7:09

brabec

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