1. HTTP Clients

Spring Boot offers a number of starters that work with HTTP clients. This section answers questions related to using them.

1.1. Configure RestTemplate to Use a Proxy

As described in boot-features-resttemplate-customization, you can use a RestTemplateCustomizer with RestTemplateBuilder to build a customized RestTemplate. This is the recommended approach for creating a RestTemplate configured to use a proxy.

The exact details of the proxy configuration depend on the underlying client request factory that is being used. The following example configures HttpComponentsClientRequestFactory with an HttpClient that uses a proxy for all hosts except

static class ProxyCustomizer implements RestTemplateCustomizer {

    public void customize(RestTemplate restTemplate) {
        HttpHost proxy = new HttpHost("proxy.example.com");
        HttpClient httpClient = HttpClientBuilder.create().setRoutePlanner(new DefaultProxyRoutePlanner(proxy) {

            public HttpHost determineProxy(HttpHost target, HttpRequest request, HttpContext context)
                    throws HttpException {
                if (target.getHostName().equals("")) {
                    return null;
                return super.determineProxy(target, request, context);

        restTemplate.setRequestFactory(new HttpComponentsClientHttpRequestFactory(httpClient));


1.2. Configure the TcpClient used by a Reactor Netty-based WebClient

When Reactor Netty is on the classpath a Reactor Netty-based WebClient is auto-configured. To customize the client’s handling of network connections, provide a ClientHttpConnector bean. The following example configures a 60 second connect timeout and adds a ReadTimeoutHandler:

ClientHttpConnector clientHttpConnector(ReactorResourceFactory resourceFactory) {
    TcpClient tcpClient = TcpClient.create(resourceFactory.getConnectionProvider())
            .runOn(resourceFactory.getLoopResources()).option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 60000)
            .doOnConnected((connection) -> connection.addHandlerLast(new ReadTimeoutHandler(60)));
    return new ReactorClientHttpConnector(HttpClient.from(tcpClient));
Note the use of ReactorResourceFactory for the connection provider and event loop resources. This ensures efficient sharing of resources for the server receiving requests and the client making requests.