Spring Boot GraphQL订阅报错：当前链过滤器/Servlet不支持异步操作

访问端点时触发如下异常：

java.lang.IllegalStateException: A filter or servlet of the current chain does not support asynchronous operations.
...

应用相关组件说明 #

pom.xml依赖配置 #

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-graphql</artifactId>
</dependency>
<dependency>
    <groupId>com.graphql-java-kickstart</groupId>
    <artifactId>graphql-spring-boot-starter</artifactId>
    <version>15.1.0</version>
</dependency>

GraphQL Resolver代码 #

@Component
public class GraphQLResolver implements GraphQLQueryResolver,GraphQLSubscriptionResolver {
    public Publisher<Comment> allComments() {
       List<Comment> comments = Arrays.asList(restTemplate().getForObject(apiUrl, Comment[].class));
       return Flux.fromIterable(comments);
    }
}

GraphQL Schema定义 #

schema {
    subscription: Subscription
}

type Subscription {
    allComments: Comment
}

type Comment {
    postId: String
    id: String
    name: String
    email: String
    body: String
}

问题原因及解决方法 #

1. 依赖冲突：同时引入Spring官方spring-boot-starter-graphql和第三方graphql-spring-boot-starter，两者的Servlet处理逻辑不兼容，导致异步支持失效。

   • 处理：移除其中一个依赖，优先保留Spring官方的spring-boot-starter-graphql，它对Spring生态的异步支持更适配。

2. 开启Servlet异步支持：如果必须保留两个依赖，需手动开启Servlet异步支持：

   • 在application.properties中添加配置：

     spring.graphql.servlet.async-supported=true
     

   • 或者自定义Servlet注册Bean：

     @Configuration
     public class GraphQLServletConfig {
         @Bean
         public ServletRegistrationBean<GraphQLServlet> graphQLServletRegistrationBean(GraphQLServlet graphQLServlet) {
             ServletRegistrationBean<GraphQLServlet> registrationBean = new ServletRegistrationBean<>(graphQLServlet, "/graphql");
             registrationBean.setAsyncSupported(true);
             return registrationBean;
         }
     }
     

3. 订阅逻辑优化：当前Resolver返回的是静态列表转换的Flux，不符合订阅实时推送的设计初衷。如果要实现真正的订阅功能，应该使用事件驱动的Publisher，比如通过Flux.create创建可推送的流：

   private final Sinks.Many<Comment> commentSink = Sinks.many().multicast().onBackpressureBuffer();
   
   public Publisher<Comment> allComments() {
       // 这里可以添加事件监听逻辑，比如当有新Comment时调用commentSink.tryEmitNext(comment)
       return commentSink.asFlux();
   }
   

内容的提问来源于stack exchange，提问作者Ajit Barik