Order

This paper mainly studies the encapsulation of HttpClient of reactor-netty by WebClient of spring 5.

DefaultWebClientBuilder

spring-webflux-5.0.2.RELEASE-sources.jar! /org/springframework/web/reactive/function/client/DefaultWebClientBuilder.java

    @Override
    public WebClient build() {
        ExchangeFunction exchange = initExchangeFunction();
        ExchangeFunction filteredExchange = (this.filters != null ? this.filters.stream()
                .reduce(ExchangeFilterFunction::andThen)
                .map(filter -> filter.apply(exchange))
                .orElse(exchange) : exchange);
        return new DefaultWebClient(filteredExchange, initUriBuilderFactory(),
                unmodifiableCopy(this.defaultHeaders), unmodifiableCopy(this.defaultCookies),
                new DefaultWebClientBuilder(this));
    }    

The build here calls the initExchangeFunction method

    private ExchangeFunction initExchangeFunction() {
        if (this.exchangeFunction != null) {
            return this.exchangeFunction;
        }
        else if (this.connector != null) {
            return ExchangeFunctions.create(this.connector, this.exchangeStrategies);
        }

        else {
            return ExchangeFunctions.create(new ReactorClientHttpConnector(), this.exchangeStrategies);
        }
    }

New here is a ReactorClientHttpConnector

ReactorClientHttpConnector

spring-web-5.0.2.RELEASE-sources.jar! /org/springframework/http/client/reactive/ReactorClientHttpConnector.java

    /**
     * Create a Reactor Netty {@link ClientHttpConnector}
     * with default {@link ClientOptions} and HTTP compression support enabled.
     */
    public ReactorClientHttpConnector() {
        this.httpClient = HttpClient.builder()
                .options(options -> options.compression(true))
                .build();
    }

You can see that this constructor uses reactor/ipc/netty/http/client/http client

DefaultWebClient

spring-webflux-5.0.2.RELEASE-sources.jar! /org/springframework/web/reactive/function/client/DefaultWebClient.java

    @Override
    public RequestHeadersUriSpec<?> get() {
        return methodInternal(HttpMethod.GET);
    }

    @Override
    public RequestHeadersUriSpec<?> head() {
        return methodInternal(HttpMethod.HEAD);
    }

    @Override
    public RequestBodyUriSpec post() {
        return methodInternal(HttpMethod.POST);
    }

    @Override
    public RequestBodyUriSpec put() {
        return methodInternal(HttpMethod.PUT);
    }

    @Override
    public RequestBodyUriSpec patch() {
        return methodInternal(HttpMethod.PATCH);
    }

    @Override
    public RequestHeadersUriSpec<?> delete() {
        return methodInternal(HttpMethod.DELETE);
    }

    @Override
    public RequestHeadersUriSpec<?> options() {
        return methodInternal(HttpMethod.OPTIONS);
    }

    @Override
    public RequestBodyUriSpec method(HttpMethod httpMethod) {
        return methodInternal(httpMethod);
    }

    @SuppressWarnings("unchecked")
    private RequestBodyUriSpec methodInternal(HttpMethod httpMethod) {
        return new DefaultRequestBodyUriSpec(httpMethod);
    }

DefaultWebClient mainly returns RequestHeadersUriSpec or RequestBodyUriSpec to GET, HEAD, POST, PUT, PATCH, DELETE, OPTIONS method packages

        @Override
        public Mono<ClientResponse> exchange() {
            ClientRequest request = (this.inserter != null ?
                    initRequestBuilder().body(this.inserter).build() :
                    initRequestBuilder().build());
            return exchangeFunction.exchange(request).switchIfEmpty(NO_HTTP_CLIENT_RESPONSE_ERROR);
        }

Finally, the call to the exchangeFunction is encapsulated in the exchange method, where switchfunction returns reactor.core.publisher.monoswitchifempty < clientresponse >

spring-webflux-5.0.2.RELEASE-sources.jar! /org/springframework/web/reactive/function/client/ExchangeFunctions.java

        public Mono<ClientResponse> exchange(ClientRequest request) {
            Assert.notNull(request, "'request' must not be null");
            return this.connector
                    .connect(request.method(), request.url(),
                            clientHttpRequest -> request.writeTo(clientHttpRequest, this.strategies))
                    .log("org.springframework.web.reactive.function.client", Level.FINE)
                    .map(clientHttpResponse -> new DefaultClientResponse(clientHttpResponse,
                            this.strategies));
        }

The connect method of ReactorClientHttpConnector is called here

spring-web-5.0.2.RELEASE-sources.jar! /org/springframework/http/client/reactive/ReactorClientHttpConnector.java

    public Mono<ClientHttpResponse> connect(HttpMethod method, URI uri,
            Function<? super ClientHttpRequest, Mono<Void>> requestCallback) {

        if (!uri.isAbsolute()) {
            return Mono.error(new IllegalArgumentException("URI is not absolute: " + uri));
        }

        return this.httpClient
                .request(adaptHttpMethod(method),
                        uri.toString(),
                        request -> requestCallback.apply(adaptRequest(method, uri, request)))
                .map(this::adaptResponse);
    }

Request method for HttpClient of reactor-netty last called by connect method.

Summary

The webflux part of spring 5 is mainly based on reactor project, and WebClient is also implemented based on reactor-netty, which mainly encapsulates some UriSpec and other convenient methods.

See spring-webflux-5.0.2.release-sources.jar! /org/springframework/web/reactive/function/client/WebClient.java