How are requests to the controller processed and can they be executed simultaneously or sequentially?

In Java web applications (for example, on Spring MVC), controllers are usually singletons and handle requests in a multithreaded manner. This means that multiple requests to the same controller can be processed simultaneously in different threads.

It is important that there is no state in the controller that depends on a specific request (for example, class fields that are modified), otherwise there may be thread safety issues.

If sequential processing of requests is required, it must be implemented explicitly (for example, through synchronization), but this is usually not necessary and reduces performance.

Example:

@RestController
public class MyController {
    @GetMapping("/data")
    public String getData() {
        // Local variables are safe
        return "response";
    }
}

Here, multiple requests can be processed simultaneously.