How would you use the Chain of Responsibility pattern to implement a request-processing pipeline (such as middleware-style validation/authentication/logging), and how does this relate conceptually to servlet filters or web framework middleware?

Chain of Responsibility passes a request sequentially through a chain of independent handler objects, each deciding whether to process the request itself, pass it along to the next handler in the chain, or short-circuit the chain entirely (e.g., rejecting an unauthenticated request before it reaches business logic) -- this is conceptually exactly how servlet Filters, ASP.NET Core middleware, and similar web framework request pipelines work: each handler/filter/middleware component wraps and potentially short-circuits the remainder of the chain, letting cross-cutting concerns (auth, logging, rate limiting) be composed independently and reordered without modifying the core request-handling logic itself.

public abstract class Handler {
    protected Handler next;
    public Handler setNext(Handler next) { this.next = next; return next; }
    public abstract void handle(Request request);
}

class AuthHandler extends Handler {
    public void handle(Request request) {
        if (!request.isAuthenticated()) { throw new SecurityException("Unauthorized"); }
        if (next != null) next.handle(request);  // pass along the chain
    }
}

Handler chain = new AuthHandler();
chain.setNext(new LoggingHandler()).setNext(new BusinessLogicHandler());
chain.handle(incomingRequest);