Apache Camel 通过 Eureka 发现服务并调用 | Camel 集成 Spring Cloud 服务发现

本文基于 Camel 3.2.0 进行实践

前言

最近本人在研究 Camel 相关技术，现在有个问题，Camel 如何接入已有的微服务架构的系统中，进行服务发现并通过 REST 调用各项服务？

Apache Camel Spring Boot Starters 官方文档：
https://camel.apache.org/camel-spring-boot/latest/index.html

组件 spring-cloud-netflix 官方文档：
https://camel.apache.org/camel-spring-boot/latest/spring-cloud-netflix.html

Camel 官方文档对 Spring Cloud 这块的内容不是很详细，只是粗略描述。

使用方式

使用 Camel Spring Boot Starter

如果要接入 Spring Cloud 体系，首先，Camel 应用要基于 Spring Boot 启动。

引入相关依赖

本文实践版本：

Camel Spring Cloud + Eureka 相关依赖：

    implementation "org.apache.camel.springboot:camel-service-starter"
    implementation "org.apache.camel.springboot:camel-spring-cloud-starter"
    implementation "org.apache.camel.springboot:camel-spring-cloud-netflix-starter"
    implementation "org.apache.camel.springboot:camel-ribbon-starter"
    implementation "org.springframework.cloud:spring-cloud-starter-netflix-eureka-client"

build.gradle 参考示例：

plugins {
    id 'org.springframework.boot' version '2.2.6.RELEASE'
    id 'io.spring.dependency-management' version '1.0.9.RELEASE'
    id 'java'
}

group = 'vip.wuweijie.camel.runtime'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'

ext {
    camelVersion = '3.2.0'
    springCloudVersion = 'Hoxton.SR3'
}

repositories {
    mavenLocal()
    maven { url "http://maven.aliyun.com/nexus/content/groups/public/" }
    mavenCentral()
    maven { url "https://repo.spring.io/milestone" }
}

dependencyManagement {
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
    }
    imports {
        mavenBom "org.apache.camel.springboot:camel-spring-boot-dependencies:${camelVersion}"
    }
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-actuator'
    implementation "org.apache.camel.springboot:camel-spring-boot-starter"
    implementation "org.apache.camel.springboot:camel-zipkin-starter"

    implementation "org.apache.camel.springboot:camel-http-starter"
    implementation "org.apache.camel.springboot:camel-netty-http-starter"
    implementation "org.apache.camel.springboot:camel-netty-starter"

    implementation "org.apache.camel.springboot:camel-ribbon-starter"
    implementation "org.apache.camel.springboot:camel-service-starter"
    implementation "org.apache.camel.springboot:camel-spring-cloud-starter"
    implementation "org.apache.camel.springboot:camel-spring-cloud-netflix-starter"
    implementation "org.springframework.cloud:spring-cloud-starter-netflix-eureka-client"

    testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

相关配置

按照正常配置 Spring Boot Eureka Client 的方式：

eureka:
  client:
    register-with-eureka: false
    fetch-registry: false
    service-url: 
      defaultZone: http://eureka.sia.lo:8761/eureka
spring:
  application:
    name: simple-micro-service

微服务调用示例

如图，Eureka 中有两个服务：

• SIMPLE-MICRO-SERVICE：提供服务
• CAMEL-MICRO-SERVICE：接入微服务的 Camel
  

其中，SIMPLE-MICRO-SERVICE 有个接口：

@RestController
@RequestMapping("/simple")
public class SimpleController {
    @GetMapping("/hello")
    public Mono<String> hello() {
        return Mono.just("hello, world. --simple-micro-service");
    }
}

Camel 路由：

@Component
public class SampleRoute extends RouteBuilder {
    @Override
    public void configure() throws Exception {
        restConfiguration()
                .port(8081)
        ;
        from("rest:get:simple:/{path}")
                .serviceCall("netty-http:simple-micro-service")
                .to("log:SampleRoute?showAll=true")
        ;
    }
}

请求 Camel 的 Rest 接口，结果如下：

GET http://localhost:8081/simple/hello

HTTP/1.1 200 OK
content-length: 36
content-type: text/plain;charset=UTF-8
connection: keep-alive

hello, world. --simple-micro-service

Response code: 200 (OK); Time: 30ms; Content length: 36 bytes

源码解读

相关 Jar：

• camel-api-3.2.0.jar
• camel-spring-cloud-3.2.0.jar
• spring-cloud-netflix-eureka-client-2.2.2.RELEASE.jar

camel-api 包中有个 interface ServiceDiscovery

package org.apache.camel.cloud;

import java.util.List;

/**
 * Allows SPIs to implement custom Service Discovery.
 *
 * @see ServiceChooser
 * @see ServiceDefinition
 */
public interface ServiceDiscovery {

    /**
     * Gets the list of services.
     * <p/>
     * This method may return an empty list.
     *
     * @param name the service name
     */
    List<ServiceDefinition> getServices(String name);
}

camel-spring-cloud 实现了上面的 interface CamelSpringCloudServiceDiscovery

package org.apache.camel.spring.cloud;

import java.util.List;
import java.util.stream.Collectors;

import org.apache.camel.cloud.ServiceDefinition;
import org.apache.camel.cloud.ServiceDiscovery;
import org.apache.camel.impl.cloud.DefaultServiceDefinition;
import org.springframework.cloud.client.discovery.DiscoveryClient;

public class CamelSpringCloudServiceDiscovery implements ServiceDiscovery {

    // 这里使用了 Spring Cloud 的接口 DiscoveryClient
    private final DiscoveryClient discoveryClient;

    public CamelSpringCloudServiceDiscovery(DiscoveryClient discoveryClient) {
        this.discoveryClient = discoveryClient;
    }

    @Override
    public List<ServiceDefinition> getServices(String name) {
        return discoveryClient.getInstances(name).stream()
            .map(
                si -> {
                    return DefaultServiceDefinition.builder()
                        .withName(si.getServiceId())
                        .withHost(si.getHost())
                        .withPort(si.getPort())
                        .withId(name)
                        .withMeta(si.getMetadata())
                        .build();
                }
            ).collect(Collectors.toList());
    }
}

上述代码调用了 DiscoveryClient 接口，这个接口有很多实现类，其中就包括了 spring-cloud-netflix-eureka-client 提供的 EurekaDiscoveryClient

Camel 没有直接提供对 Eureka 的支持，但提供了对 Spring Cloud Discovery 相关支持，所以可以选择 Eureka 作为 Spring Cloud 的服务发现，从而让 Camel 与 Eureka 集成。