SpringMVC where to put common code between controller's methods - spring

Question

I'm working on an existing codebase and I'm seeing this pattern in all the controller methods. Same variables are declared in the beginning and the code is placed inside the try catch block which is also same across all the methods. I was wondering if there's a way to push the common code across methods inside a BaseController. So that I don't have to declare the common variables inside each method and the try catch block functionality is also delegated to someplace else.
At first, I created a BaseController class, annotated it with #Controller annotation and extended my controller to be its subclass. Then I moved all the common variables to the BaseController. The problem is, once I modify these variables inside the controller's method, they retain their values even in the next request which is problematic.
#RequestMapping(value = "/delete/{id}", method = RequestMethod.GET)
public ResponseEntity delete(#PathVariable("id") Integer id)
{
HashMap response = new HashMap();
boolean success = false;
List errors = new ArrayList();
HttpStatus httpStatus = HttpStatus.BAD_REQUEST;
String message = "";
try
{
purchaseInvoiceService.delete(id);
success = true;
message = "Purchase Invoice Deleted";
httpStatus = HttpStatus.OK;
} catch (Exception e)
{
errors.add(new ErrorMessage("error", e.getMessage()));
e.printStackTrace();
}
response.put("success", success);
response.put("errors", errors);
response.put("message", message);
return new ResponseEntity(response, httpStatus);
}
I want to refactor this patter so that in each method I just have to contain only the call to the service and conditionally setting the success and httpstatus variable (present in BaseController) and then returning the response using response() method present in BaseController which adds the data variable and it's return type is ResponseEntity.
Edit 1:
This endpoint returns a list of all purchase invoices, currently, its just returning the HashMap which gets converted to JSON. The point I'm trying to make is that these response, success, errors, httpStatus variables and the part where all these variables are put in response HashMap() are a part of every method inside each controller, I'd like to refactor these to something similar to ResponseFactory as well. So I'm thinking to pass the List to ResponseFactory as well which will then structure all the response and return in the form of ResponseEntity. Just want to know if I'm doing it correctly.
#RequestMapping(method = RequestMethod.GET)
public ResponseEntity getAll() {
HashMap response = new HashMap();
boolean success = false;
List errors = new ArrayList();
HttpStatus httpStatus = HttpStatus.BAD_REQUEST;
String message = "";
Map data = new HashMap();
try {
List<PurchaseInvoice> purchaseInvoices = purchaseInvoiceService.getAll();
data.put("purchaseInvoices", purchaseInvoices);
success = true;
message = "Purchase Invoice List";
httpStatus = httpStatus.OK;
} catch (Exception e) {
errors.add(new ErrorMessage("error", e.getMessage()));
e.printStackTrace();
}
response.put("success", success);
response.put("errors", errors);
response.put("message", message);
response.put("data", data);
return new ResponseEntity(response, httpStatus);
}

Answer 1

Your phrase: "Then I moved all the common variables to the BaseController" sounds confusing.
A controller in spring is just a Singleton with an additional "ability" provided by spring: its something that is exposed as a web endpoint (less relevant for your specific question).
Being Singleton means that there is one instance in the ApplicationContext.
So if the variables were moved like this:
class BaseController {
protected Field1 field1;
protected Field2 field2;
....
}
Then there is certainly a problem, you've actually introduced a state to the controller, and this state is shared among all the requests.
Long story short, don't create stateful controllers
Having said that the idea of refactoring is good. Just the way to refactor probably is wrong:
Instead, I suggest to consider the following refactoring:
Create class responseFactory with some static methods:
class ResponseFactory {
public static ResponseEntity success(String message) {
here prepare the map with boolean success and everything
}
}
Now the controller becomes:
class Controller {
public ResponseEntity delete(#PathVariable("id") Integer id) {
purchaseInvoiceService.delete(id); // I'll talk about exceptions later
return ResponseEntityFactory.success("Purchase Invoice Deleted");
}
}
Now as for exceptions - this is somewhat confusing - the code basically says that the response would be successful despite the errors.
So if you have to leave it like this, the ResponseEntityFactory will have to get the List of errors as well or something, but in general, Spring has a pretty powerful exception handling mechanism to map the exceptions thrown on the backend (service, DAO, whatever) to the meaningful non-200 response.