Explain how and why requests can be processed in one or multiple threads in a web application controller

In web applications, controllers handle HTTP requests. Processing can be:

• Single-threaded — all requests are processed sequentially in one thread. This is simple but inefficient under high load.

• Multi-threaded — each request is processed in a separate thread or thread pool, allowing multiple users to be served concurrently.

The reason for using multithreading is to improve the performance and responsiveness of the application. For example, in Java servlets, the container creates a new thread for each request or takes one from the pool.

It is important to consider thread safety: data shared between requests should be synchronized or used in thread-safe structures.