How to do sequence of operations and ensure one operation is complete before next one in Spring Reactor web app?

Question

I have Spring Boot 2 web app in which I need to identify site visitor by cookie and gather page view stats. So I need to intercept every web request. The code I had to write is

Answer 1

Another variant which creates pageview and updates the user in the webfilter in a non-blocking way, before passing a request to the controller:

@Bean
public WebFilter filter() {
    return (exchange, chain) -> {
        ServerHttpRequest req = exchange.getRequest();
        String uri = req.getURI().toString();
        log.info("[i] Web Filter: received the request: {}", uri);

        var headers = req.getHeaders();
        List tokenList = headers.get("token");

        if (tokenList != null && tokenList.get(0) != null) {
            String token = tokenList.get(0);
            Mono foundUser = userRepo
                    .findByToken(token)
                    .doOnNext(user -> log.info("[i] Web Filter: {} has been found", user));
            return updateUserStat(foundUser, exchange, chain, uri);
        } else {
            String token = UUID.randomUUID().toString();
            Mono createdUser = userRepo
                    .save(new User(token))
                    .doOnNext(user -> log.info("[i] Web Filter: a new {} has been created", user));
            return updateUserStat(createdUser, exchange, chain, uri);
        }
    };
}

private Mono updateUserStat(Mono userMono, ServerWebExchange exchange, WebFilterChain chain, String uri) {
    return userMono
            .doOnNext(user -> exchange.getAttributes().put("_token", user.getToken()))
            .doOnNext(u -> {
                String token = exchange.getAttribute("_token");
                log.info("[i] Web Filter: token attribute has been set to '{}'", token);
            })
            .flatMap(user -> pageViewRepo.save(new PageView(uri)).flatMap(user::addPageView).flatMap(userRepo::save))
            .doOnNext(user -> {
                int numberOfPages = 0;
                List pageViews = user.getPageViews();
                if (pageViews != null) {
                    numberOfPages = pageViews.size();
                }
                log.info("[i] Web Filter: {} has been updated. Number of pages: {}", user, numberOfPages);
            })
            .then(chain.filter(exchange));
}

This code produces the following results:

1) Token is not present: create a new user, create a page view, update the new user, pass a request to controller

2019-01-20 14:39:10.033 [ctor-http-nio-3] : [i] Web Filter: received the request: http://localhost:8080/users?test=784
2019-01-20 14:39:10.110 [ctor-http-nio-3] : Inserting Document containing fields: [token, _class] in collection: user
2019-01-20 14:39:10.206 [ntLoopGroup-2-2] : [i] Web Filter: a new User(id=5c446bee24c86426ac6c0ae5, token=fba944cd-decb-4923-9757-724da5a60061) has been created
2019-01-20 14:39:10.212 [ntLoopGroup-2-2] : [i] Web Filter: token attribute has been set to 'fba944cd-decb-4923-9757-724da5a60061'
2019-01-20 14:39:11.227 [     parallel-1] : Inserting Document containing fields: [URL, createdDate, _class] in collection: pageView
2019-01-20 14:39:11.242 [ntLoopGroup-2-2] : Saving Document containing fields: [_id, token, pageViews, _class]
2019-01-20 14:39:11.256 [ntLoopGroup-2-2] : [i] Web Filter: User(id=5c446bee24c86426ac6c0ae5, token=fba944cd-decb-4923-9757-724da5a60061) has been updated. Number of pages: 1
2019-01-20 14:39:11.289 [ntLoopGroup-2-2] : [i] Controller: handling 'get all users' request. Token attribute is 'fba944cd-decb-4923-9757-724da5a60061'
2019-01-20 14:39:11.369 [ntLoopGroup-2-2] : find using query: { } fields: Document{{}} for class: class io.github.cepr0.demo.User in collection: user

2) Token is present: find an existing user, create a page view, update the user, pass a request to controller

2019-01-20 14:51:21.983 [ctor-http-nio-3] : [i] Web Filter: received the request: http://localhost:8080/users?test=538
2019-01-20 14:51:22.074 [ctor-http-nio-3] : Created query Query: { "token" : "b613b810-cc36-4961-ad2e-db44f52cd2dd" }, Fields: { }, Sort: { }
2019-01-20 14:51:22.092 [ctor-http-nio-3] : find using query: { "token" : "b613b810-cc36-4961-ad2e-db44f52cd2dd" } fields: Document{{}} for class: class User in collection: user
2019-01-20 14:51:22.102 [ntLoopGroup-2-2] : [i] Web Filter: User(id=5c434c2eb338ac3530cbd56d, token=b613b810-cc36-4961-ad2e-db44f52cd2dd) has been found
2019-01-20 14:51:22.102 [ntLoopGroup-2-2] : [i] Web Filter: token attribute has been set to 'b613b810-cc36-4961-ad2e-db44f52cd2dd'
2019-01-20 14:51:23.103 [     parallel-2] : Inserting Document containing fields: [URL, createdDate, _class] in collection: pageView
2019-01-20 14:51:23.115 [ntLoopGroup-2-2] : Saving Document containing fields: [_id, token, pageViews, _class]
2019-01-20 14:51:23.117 [ntLoopGroup-2-2] : [i] Web Filter: User(id=5c434c2eb338ac3530cbd56d, token=b613b810-cc36-4961-ad2e-db44f52cd2dd) has been updated. Number of pages: 13
2019-01-20 14:51:23.118 [ntLoopGroup-2-2] : [i] Controller: handling 'get all users' request. Token attribute is 'b613b810-cc36-4961-ad2e-db44f52cd2dd'
2019-01-20 14:51:23.119 [ntLoopGroup-2-2] : find using query: { } fields: Document{{}} for class: class User in collection: user

3) Token is present but user is not found: pass a request to controller

2019-01-20 14:52:41.842 [ctor-http-nio-3] : [i] Web Filter: received the request: http://localhost:8080/users?test=513
2019-01-20 14:52:41.844 [ctor-http-nio-3] : Created query Query: { "token" : "-b613b810-cc36-4961-ad2e-db44f52cd2dd" }, Fields: { }, Sort: { }
2019-01-20 14:52:41.845 [ctor-http-nio-3] : find using query: { "token" : "-b613b810-cc36-4961-ad2e-db44f52cd2dd" } fields: Document{{}} for class: class User in collection: user
2019-01-20 14:52:41.850 [ntLoopGroup-2-2] : [i] Controller: handling 'get all users' request. Token attribute is 'null'
2019-01-20 14:52:41.850 [ntLoopGroup-2-2] : find using query: { } fields: Document{{}} for class: class User in collection: user

Demo: sb-reactive-filter-demo(branch: update-user-in-web-filter)