private WebApplicationType deduceWebApplicationType() {
        if (ClassUtils.isPresent("org.springframework.web.reactive.DispatcherHandler", (ClassLoader)null
 
) && !ClassUtils.isPresent("org.springframework.web.servlet.DispatcherServlet", (ClassLoader)null) && !ClassUtils.isPresent("org.glassfish.jersey.server.ResourceConfig", (ClassLoader)null)) {
            return WebApplicationType.REACTIVE;
        } else {
            String[] var1 = WEB_ENVIRONMENT_CLASSES;
            
 
int var2 = var1.length;

            for(int var3 = 0; var3 < var2; ++var3) {
                String className = var1[var3];
                if (!ClassUtils.isPresent(className, (ClassLoader)null)) {
                    return WebApplicationType.NONE;
                }
            }

            return
 
 WebApplicationType.SERVLET;
        }
    }

WebServer在org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext創建

    protected void onRefresh() {
        super.onRefresh();

        try {
            this.createWebServer();
        } catch (Throwable var2) {
            throw new ApplicationContextException("Unable to start reactive web server", var2);
        }
    }

Spring boot加載REACTIVE程序過程