如何在 Spring Cloud Stream 中配置函数的绑定以将其输入绑定到 Web 端点并将其输出绑定到 Kafka 主题

Question

我有一个普通的 java Function；我正在尝试绑定：

它对网络端点的输入
它输出到一个kafka主题。

当我在 web 上下文中使用我的函数时，它总是 returns 将 Function 的结果值单独返回给 web 客户端。我可以做这样的事情吗？:

spring.cloud.stream.bindings.input.binder=web
spring.cloud.stream.bindings.output.binder=kafka

我目前正在尝试将 Function 拆分为 2:

一个输入绑定到网络客户端，输出动态绑定到第二个函数（使用 spring.cloud.stream.sendto.destination）
另一个函数，其输出绑定到 kafka 绑定。

这个方法还是不行。动态路由 (spring.cloud.stream.sendto.destination) 显示在 Web 客户端上；但是没有 Message 被发送到 kafka 绑定本身。这是我在第二种方法（2 个函数）中使用的代码，希望简单地获得一个 Spring 功能应用程序，将其输入绑定到 Web 端点并输出到 kafka 主题。

WebToKafkaApp.java

@SpringBootApplication
public class WebToKafkaApp {
    public static void main(String[] args) {
        SpringApplication.run(WebToKafkaApp.class, args);
    }

    @Bean
    public Function<String, Message<String>> webFunction() {
        return payload -> createPayloadMapperToMessage("kafkaFunction").apply(payload);
    }

    @Bean
    public Function<Flux<Message<String>>, Flux<Message<String>>> kafkaFunction() {
        return flux -> flux.map(msg -> createPayloadMapperToMessage("").apply(msg.getPayload()));
    }

    private Function<String, Message<String>> createPayloadMapperToMessage(String destination) {
        return payload -> MessageBuilder
                .withPayload(payload.toUpperCase())
                .setHeader("spring.cloud.stream.sendto.destination", destination)
                .build();
    }
}

application.yml

spring.cloud.stream.bindings.webFunction-in-0:
  destination: webFunctionIN
  contentType: application/json
spring.cloud.stream.bindings.webFunction-out-0:
  destination: webFunctionOUT
  contentType: application/json
spring.cloud.stream.bindings.kafkaFunction-in-0:
  destination: kafkaFunctionIN
  contentType: application/json
  binder: kafka
spring.cloud.stream.bindings.kafkaFunction-out-0:
  destination: kafkaFunctionOUT
  contentType: application/json
  binder: kafka

spring:
  cloud:
    stream:
      kafka:
        binder:
          brokers: localhost:9092

spring.cloud.stream.function.routing.enabled: true
spring.cloud.function.definition: webFunction

build.gradle

plugins {
    id 'org.springframework.boot' version '2.2.1.RELEASE'
    id 'io.spring.dependency-management' version '1.0.8.RELEASE'
    id 'java'
}
group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'
repositories {
    mavenCentral()
}
ext {
    set('springCloudVersion', "Hoxton.RELEASE")
}
dependencies {
    implementation 'org.springframework.boot:spring-boot-starter'
    implementation 'org.springframework.cloud:spring-cloud-starter-function-web'
    implementation 'org.springframework.cloud:spring-cloud-starter-function-webflux'
    implementation 'org.springframework.cloud:spring-cloud-stream'
    implementation 'org.springframework.cloud:spring-cloud-starter-stream-kafka'
    testImplementation('org.springframework.boot:spring-boot-starter-test') {
        exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
    }
}
dependencyManagement {
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
    }
}
test {
    useJUnitPlatform()
}

如有任何帮助，我们将不胜感激。

Answer 1

感谢 Oleg for posting 。本质上，我增强了他的建议，以一般地处理以下之间的桥梁：

一个功能性的网络控制器；可以接收网络请求。
流媒体供应商；它可以将任何消息转发到消息传递基础结构。

此解决方案将中描述的问题封装在 Supplier 的自定义实现中。这样的实现公开了一个 API 来触发 Supplier 发出作为参数传递的消息。这样的 class 将如下所示：

import org.springframework.messaging.Message;
import org.springframework.messaging.support.MessageBuilder;

import java.util.function.Supplier;

import reactor.core.publisher.EmitterProcessor;
import reactor.core.publisher.Flux;

public class StreamSupplier implements Supplier<Flux<?>> {

    private static final String SPRING_CLOUD_STREAM_SENDTO_DESTINATION =
            "spring.cloud.stream.sendto.destination";

    public static <T> Message<?> createMessage(T payload, String destination) {
        MessageBuilder<T> builder = MessageBuilder.withPayload(payload);
        if (destination != null && !destination.isEmpty())
            builder.setHeader(SPRING_CLOUD_STREAM_SENDTO_DESTINATION, destination);
        return builder.build();
    }

    private String defaultDestination;
    private EmitterProcessor<? super Object> processor = EmitterProcessor.create();

    public StreamSupplier() {
        this(null);
    }

    public StreamSupplier(String defaultDestination) {
        this.defaultDestination = defaultDestination;
    }

    // SEND APIs

    public <T> Message<?> sendMessage(T payload) {
        return sendMessage(payload, defaultDestination);
    }

    public <T> Message<?> sendMessage(T payload, String destination) {
        return sendBody(createMessage(payload, destination));
    }

    public <T> T sendBody(T body) {
        processor.onNext(body);
        return body;
    }

    /**
     * Returns {@link EmitterProcessor} used internally to programmatically publish messages onto
     * the output binding associated with this {@link Supplier}. Such programmatic publications
     * are available through the {@code sendXXX} API methods available in this class.
     */
    @Override
    public Flux<?> get() {
        return processor;
    }
}

那么开发人员只需：

在 Spring 应用程序中将此特定 Supplier 实现的实例注册为 bean；并让 spring-cloud-function 将此 bean 扫描到 FunctionCatalog.
创建一个 web function，使用之前注册的 Supplier 将任何消息转发到流媒体基础设施 - 可以使用 spring-cloud-stream 的所有功能进行配置。

以下示例演示了这一点：

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Controller;

import java.util.function.Function;
import java.util.function.Supplier;

import reactor.core.publisher.Flux;

@SpringBootApplication
@Controller
public class MyApp {

    public static void main(String[] args) {
        SpringApplication.run(MyApp.class,
                "--spring.cloud.function.definition=streamSupplierFunction;webToStreamFunction");
    }

    // Functional Web Controller
    @Bean
    public Function<String, String> webToStreamFunction() {
        return msg -> streamSupplier().sendBody(msg);
    }

    // Functional Stream Supplier
    @Bean
    public Supplier<Flux<?>> streamSupplierFunction() {
        return new StreamSupplier();
    }

    // DOUBLE REGISTRATION TO AVOID POLLABLE CONFIGURATION
    // LIMITATION OF SPRING-CLOUD-FUNCTION
    @Bean
    public StreamSupplier streamSupplier() {
        return (StreamSupplier) streamSupplierFunction();
    }
}

再次感谢Oleg for providing the 我一直在寻找构建这个全面的解决方案。

Complete code on GitHub

如何在 Spring Cloud Stream 中配置函数的绑定以将其输入绑定到 Web 端点并将其输出绑定到 Kafka 主题

How to configure the bindings of a function in Spring Cloud Stream to bind its input to a web endpoint and its output to a Kafka topic

java

java-8

spring-boot

functional-interface

spring-cloud