Spring Cloud构建微服务架构基础

使用LoadBalancerClient

在Spring Cloud Commons中提供了大量的与服务治理相关的抽象接口，包括DiscoveryClient、这里我们即将介绍的LoadBalancerClient等。对于这些接口的定义我们在上一篇介绍服务注册与发现时已经说过，Spring Cloud做这一层抽象，很好的解耦了服务治理体系，使得我们可以轻易的替换不同的服务治理设施。

从LoadBalancerClient接口的命名中，我们就知道这是一个负载均衡客户端的抽象定义，下面我们就看看如何使用Spring Cloud提供的负载均衡器客户端接口来实现服务的消费。

下面的例子，我们将利用上一篇中构建的eureka-server作为服务注册中心、eureka-client作为服务提供者作为基础。

• 我们先来创建一个服务消费者工程，命名为：eureka-consumer。并在pom.xml中引入依赖（这里省略了parent和dependencyManagement的配置）：

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• 配置application.properties，指定eureka注册中心的地址：

spring.application.name=eureka-consumer

server.port=2101

 

eureka.client.serviceUrl.defaultZone=http://localhost:1001/eureka/

• 创建应用主类。初始化RestTemplate，用来真正发起REST请求。@EnableDiscoveryClient注解用来将当前应用加入到服务治理体系中。

@EnableDiscoveryClient

@SpringBootApplication

public class Application {

 

@Bean

public RestTemplate restTemplate() {

return new RestTemplate();

}

 

public static void main(String[] args) {

new SpringApplicationBuilder(Application.class).web(true).run(args);

}

}

• 创建一个接口用来消费eureka-client提供的接口：

@RestController

public class DcController {

 

@Autowired

LoadBalancerClient loadBalancerClient;

@Autowired

RestTemplate restTemplate;

 

@GetMapping("/consumer")

public String dc() {

ServiceInstance serviceInstance = loadBalancerClient.choose("eureka-client");

String url = "http://" + serviceInstance.getHost() + ":" + serviceInstance.getPort() + "/dc";

System.out.println(url);

return restTemplate.getForObject(url, String.class);

}

}

可以看到这里，我们注入了LoadBalancerClient和RestTemplate，并在/consumer接口的实现中，先通过loadBalancerClient的choose函数来负载均衡的选出一个eureka-client的服务实例，这个服务实例的基本信息存储在ServiceInstance中，然后通过这些对象中的信息拼接出访问/dc接口的详细地址，最后再利用RestTemplate对象实现对服务提供者接口的调用。

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