Spring RequestScope bean 未按预期工作

Question

I'm trying to learn more about Spring bean scopes for use in a project. I've created a few test classes, and I am not getting the behavior I'd expect.

I created the following component, and I would like this bean to last for only the duration of the HTTP request.

@Component
@Scope(value = WebApplicationContext.SCOPE_REQUEST, proxyMode = ScopedProxyMode.TARGET_CLASS)
public class UserDataContainer {
    
    public int requestCount = 0;

}

The following controller uses that component.

@Controller
@RequestMapping("/hello")
public class HelloController {
    
    @Autowired
    private UserDataContainer userData;

    @GetMapping
    public String get(Model model) {
        model.addAttribute("prev", userData.requestCount);
        
        userData.requestCount++;
        
        model.addAttribute("curr", userData.requestCount);
        
        return "test";
    }

}

My trouble is, it doesn't seem that a new instance of UserDataContainer is created for each request. Whenever I load this page, I see that the values of "prev" and "curr" keep incrementing, instead of resetting to 0 at the start of each request. Am I misunderstanding how this is supposed to work, or is something not implemented correctly.

Answer 1

The issue here is that the request scoped bean is not invoked directly by your controller.

Instead the controller uses a proxy to invoke the request scoped bean (in this case, the proxy is a cglib one based on your proxy mode annotation, ie: ScopedProxyMode.TARGET_CLASS

The proxy only wraps around methods of the request scoped bean and not it's variables.

So in short, encapsulate the instance variable of your request scoped bean into a method and call that method from the Controller.

something like this:

@Component
@Scope(value = WebApplicationContext.SCOPE_REQUEST, proxyMode = ScopedProxyMode.TARGET_CLASS)
public class UserDataContainer {

   private int requestCount = 0;
   public int incrementRequestCount(){
        requestCount++;
        return requestCount;
   }

   public int getRequestCount(){
         return requestCount;
   }
} 

then in your Controller, just invoke the public methods

@GetMapping
public String get(Model model) {
    model.addAttribute("prev", userData.getRequestCount());

    model.addAttribute("curr", userData.incrementRequestCount());
    
    return "test";
}