如何防止嵌入式 netty 服务器以 [=10=]-boot-starter-webflux 启动？

Question

我想使用 Spring 的新反应式 webflux 扩展在客户端和服务器应用程序之间建立通信。

对于依赖管理，我使用 gradle。我在服务器端和客户端的 build.gradle 文件基本上是：

buildscript {
    repositories {
        mavenCentral()
        maven { url "https://repo.spring.io/snapshot" }
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:2.0.0.BUILD-SNAPSHOT")
    }
}

repositories {
    mavenCentral()
    maven { url "https://repo.spring.io/snapshot" }
}

apply plugin: 'java'
apply plugin: 'org.springframework.boot'
apply plugin: "io.spring.dependency-management" 

dependencies {
    compile("org.springframework.boot:spring-boot-starter-webflux")
}

（需要注意的是 2.0.0.BUILD-SNAPSHOT 是一个移动的目标，手头的问题可能有一天会消失到依赖项内的更改)

当我启动服务器端应用程序时，一切都正常启动，包括嵌入式 netty 服务器的启动。

但是当启动客户端应用程序时也会启动一个 netty 服务器，导致 "java.net.BindException: Address already in use"，因为客户端 netty 服务器侦听与服务器端 netty 服务器相同的端口。

我的问题是：为什么 netty 首先在客户端启动，我该如何防止它？

根据 Spring-引导文档 Spring 尝试确定是否需要 Web 支持并相应地配置 Spring 应用程序上下文。

根据文档，这可以通过调用 setWebEnvironment(false) 来覆盖。我的客户端启动代码看起来像：

@SpringBootApplication(scanBasePackages = { "com.tatics.flux.main" })
public class Client {
    public static void main(String[] args) throws Exception {
        SpringApplication app = new SpringApplication(Client.class);
        app.setWebEnvironment(false);
        app.run(Client.class, args);

        WebClient webClient = WebClient.create();

        Mono<String> result = webClient
                .post()
                .uri("http://localhost:8080/fluxService")

                // This does not work any more: .body("Hallo")
                // and must be replaced by:
                .body(BodyInserters.fromObject("Hallo"))

                .accept(MediaType.TEXT_PLAIN)
                .exchange()
                .flatMap(response -> response.bodyToMono(String.class));
    }
}

可惜netty还在启动中。我还注意到 setWebEnvironment(false) 被标记为已弃用。

任何有关如何防止 netty 启动但以其他方式保留所有 webflux 依赖项的帮助都将受到赞赏。

以下是自动配置报告的摘录：

=========================
AUTO-CONFIGURATION REPORT
=========================

Positive matches:
-----------------
...

ReactiveWebServerAutoConfiguration matched:
  - found ReactiveWebApplicationContext (OnWebApplicationCondition)

ReactiveWebServerAutoConfiguration#defaultReactiveWebServerCustomizer matched:
  - @ConditionalOnMissingBean (types: org.springframework.boot.autoconfigure.web.reactive.DefaultReactiveWebServerCustomizer; SearchStrategy: all) did not find any beans (OnBeanCondition)

ReactiveWebServerConfiguration.ReactorNettyAutoConfiguration matched:
  - @ConditionalOnClass found required class 'reactor.ipc.netty.http.server.HttpServer'; @ConditionalOnMissingClass did not find unwanted class (OnClassCondition)
  - @ConditionalOnMissingBean (types: org.springframework.boot.web.reactive.server.ReactiveWebServerFactory; SearchStrategy: all) did not find any beans (OnBeanCondition)

ReactorCoreAutoConfiguration matched:
  - @ConditionalOnClass found required classes 'reactor.core.publisher.Mono', 'reactor.core.publisher.Flux'; @ConditionalOnMissingClass did not find unwanted class (OnClassCondition)

...

Negative matches:
-----------------
...
ReactiveWebServerConfiguration.JettyAutoConfiguration:
  Did not match:
     - @ConditionalOnClass did not find required class 'org.eclipse.jetty.server.Server' (OnClassCondition)

ReactiveWebServerConfiguration.TomcatAutoConfiguration:
  Did not match:
     - @ConditionalOnClass did not find required class 'org.apache.catalina.startup.Tomcat' (OnClassCondition)

ReactiveWebServerConfiguration.UndertowAutoConfiguration:
  Did not match:
     - @ConditionalOnClass did not find required class 'io.undertow.Undertow' (OnClassCondition)

...

ReactiveWebServerConfiguration.JettyAutoConfiguration:
  Did not match:
     - @ConditionalOnClass did not find required class 'org.eclipse.jetty.server.Server' (OnClassCondition)

ReactiveWebServerConfiguration.TomcatAutoConfiguration:
  Did not match:
     - @ConditionalOnClass did not find required class 'org.apache.catalina.startup.Tomcat' (OnClassCondition)

ReactiveWebServerConfiguration.UndertowAutoConfiguration:
  Did not match:
     - @ConditionalOnClass did not find required class 'io.undertow.Undertow' (OnClassCondition)

Answer 1

您的代码的主要问题是您当前正在创建一个 SpringApplication，然后对其进行自定义 - 最终删除所有内容并运行静态方法 run(Object primarySource, String... args)。

以下应该有效：

@SpringBootApplication
public class Client {

    public static void main(String[] args) throws Exception {
        SpringApplication app = new SpringApplication(Client.class);
        app.setWebApplicationType(WebApplicationType.NONE);
        app.run(args);
    }

    @Bean
    public CommandLineRunner myCommandLineRunner() {
      return args -> {
        // we have to block here, since command line runners don't
        // consume reactive types and simply return after the execution
        String result = WebClient.create("http://localhost:8080")
                .post()
                .uri("/fluxService")
                .body("Hallo")
                .accept(MediaType.TEXT_PLAIN)
                .retrieve()
                .bodyToMono(String.class)
                .block();
        // print the result?
      };
    }
}

如果不是，请运行您的应用程序使用 --debug 标志并在您的问题中添加自动配置报告的相关部分，尤其是与服务器相关的自动配置。

Answer 2

@Brian_Clozel补充回答：

您可以通过在 application.yml:

中指定来禁用 Netty（或任何其他服务器）

spring.main.web-application-type: none

或application.properties:

spring.main.web-application-type=none

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