Issue
My question is, isn't an object created from the model in spring? So why does it give an error when it tries to inject in the following program?
@Controller
public class ContactController {
private final ContactService service;
private Model model;
public ContactController(ContactService service, Model model) {
this.service = service;
this.model = model;
}
@GetMapping("contact")
public String displayPage() {
model.addAttribute("contact", new Contact());
return "contact";
}
}
UPDATE: but this works! It means that the bean is created.(Of course, after we delete the model field from the constructor and the class)
@GetMapping("contact")
public String displayPage(Model model) {
model.addAttribute("contact", new Contact());
return "contact";
}
error:
***************************
APPLICATION FAILED TO START
***************************
Description:
Parameter 1 of constructor in com.isoft.controllers.ContactController required a bean of type 'org.springframework.ui.Model' that could not be found.
Action:
Consider defining a bean of type 'org.springframework.ui.Model' in your configuration.
Solution
The model is not a dependency to your controller. You need to return a new model, when the method is called. Otherwise, different requests would all see the same model (race-conditions, security issues, and all other kinds of nasty problems)
@Controller
public class ContactController {
private final ContactService service;
public ContactController(final ContactService service) {
this.service = service;
}
@GetMapping("contact")
public String displayPage() {
final Model model = new Model();
model.addAttribute("contact", new Contact());
return "contact";
}
}
When defining the model as dependency in the constructor, a bean of that type (and name) is looked up in the application context. Only a single instance in injected.
However, the model is request-specific and therefore needs to be injected into the handler method itself. Think @Scope("request").
@GetMapping("contact")
public String displayPage(final Model model) {
model.addAttribute("contact", new Contact());
return "contact";
}
More details can be found in the Spring Web MVC framework docs: 17.3 Implementing Controllers
Answered By - knittl
Answer Checked By - Robin (JavaFixing Admin)
