Question

I’ve got a class Module with a OneToMany binding with a class Sequence.
My aim is to show the list of Modules, and by clicking on one of them, display the associated list of Sequences
But it doesn’t work, I have a HTTP 500 error.

Here there is my controller :

@RequestMapping(value="formation", method = RequestMethod.GET)
public ModelAndView allModules() {
List<Module> allModules = moduleService.findAll();
return new ModelAndView("formation", "modules", allModules);
}

@RequestMapping(value="sequences/{module}", method = RequestMethod.GET)
public String displaySequences(@PathVariable ("module") Module module, Model model) {
List<Sequence> allSequences = sequenceService.findByModule(module);
model.addAttribute("sequences", allSequences);
return "sequences";
}

and the jsp which show the list of modules to return the list of sequences

<c:forEach items="${modules}" var="module">
            <ul>
                <li><a href="sequences/${module}">${module.titre}</a>
                    <br/>
                </li>
            </ul>
        </c:forEach>

So, where does my error come from?

It works when I do that:

    @RequestMapping(value="/sequences/{moduleId}", method = RequestMethod.GET)
public String displaySequences(@PathVariable ("moduleId") Long moduleId, Model model) {
Module module = moduleService.findById(moduleId);
model.addAttribute("module", module);
return "sequences";
}

and I change the link with :

<a href="sequences/${module}">${module.titre}

but I’d like to understand my error.

Answer 1

The reason why you weren’t able to display sequences is Spring doesn’t know how to parse this

/cmap-web/sequences/com.almerys.jpa.tomcatspring.Module@12b0f0ae

into Module instance.

You can read on this in Spring docs here in the section’s 16.3.2.2 URI Template Patterns last paragraph. I paste it here for convenience.

A @PathVariable argument can be of any simple type such as int, long, Date, etc. Spring automatically converts to the appropriate type or throws a TypeMismatchException if it fails to do so. You can also register support for parsing additional data types. See Section 16.3.3.14, “Method Parameters And Type Conversion” and Section 16.3.3.15, “Customizing WebDataBinder initialization”.