Configuring Spring WebFlux WebClient to use a custom thread pool

Question

Is it possible to configure WebClient to use a custom thread pool other than the reactor-http-nio thread pool (When using Netty)? If it is possible , can we somehow restrict that custom thread pool to run only on a particular processor core?

Answer 1

Yes. You can.

1. Create some where your own Thread Pool and EventLoopGroup (or create NioEventLoopGroup bean). For example:

   {
    Intger THREADS = 10;
   
    BasicThreadFactory THREADFACTORY = new BasicThreadFactory.Builder()
           .namingPattern("HttpThread-%d")
           .daemon(true)
           .priority(Thread.MAX_PRIORITY)
           .build();
   
    EXECUTOR = new ThreadPoolExecutor(
           THREADS,
           THREADS,
           0L,
           TimeUnit.MILLISECONDS,
           new LinkedBlockingQueue<>(),
           THREADFACTORY,
           new ThreadPoolExecutor.AbortPolicy());
   
    NioEventLoopGroup RESOURCE= new NioEventLoopGroup(THREADS,EXECUTOR);
   }
   

2. Register your own ReactorResourceFactory. And provide your own EventLoopGrooup based on custom thread Executor

   @Bean
   public ReactorResourceFactory reactorResourceFactory(NioEventLoopGroup RESOURCE) {
       ReactorResourceFactory f= new ReactorResourceFactory();
       f.setLoopResources(new LoopResources() {
           @Override
            public EventLoopGroup onServer(boolean b) {
                return RESOURCE;
               }
           });
       f.setUseGlobalResources(false);
       return f;
   }
   

3. Then register ReactorClientHttpConnector. In example below it is used custom SSL Context

   @Bean
   public ReactorClientHttpConnector reactorClientHttpConnector(ReactorResourceFactory r) throws SSLException {
       SslContext sslContext = SslContextBuilder
           .forClient()
           .trustManager(InsecureTrustManagerFactory.INSTANCE)
           .build();
       return new ReactorClientHttpConnector(r, m -> m.secure(t -> t.sslContext(sslContext)));
   }
   

4. Finally build WebClient

   @Bean
   public WebClient webClient(ReactorClientHttpConnector r) {
       return WebClient.builder().clientConnector(r).build();
   }
   

If you want to use same for WebServer. Do same configuration for ReactiveWebServerFactory.

    @Bean
    public ReactiveWebServerFactory reactiveWebServerFactory(NioEventLoopGroup RESOURCE) {
        NettyReactiveWebServerFactory factory = new NettyReactiveWebServerFactory();
        factory.addServerCustomizers(hs->hs.tcpConfiguration(s->s.runOn(RESOURCE)));
        return factory;
    }

Imports:

    import io.netty.channel.EventLoopGroup;
    import io.netty.channel.nio.NioEventLoopGroup;
    import io.netty.handler.ssl.SslContext;
    import io.netty.handler.ssl.SslContextBuilder;
    import io.netty.handler.ssl.util.InsecureTrustManagerFactory;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.DependsOn;
    import org.springframework.http.client.reactive.ReactorClientHttpConnector;
    import org.springframework.http.client.reactive.ReactorResourceFactory;
    import org.springframework.stereotype.Component;
    import org.springframework.web.reactive.function.client.WebClient;
    import reactor.netty.resources.LoopResources;
    import org.apache.commons.lang3.concurrent.BasicThreadFactory;
    import org.springframework.boot.web.embedded.netty.NettyReactiveWebServerFactory;
    import org.springframework.boot.web.reactive.server.ReactiveWebServerFactory;
    import java.util.concurrent.*;