Fegin使用客户端负载均衡器Ribbon

spring boot fegin

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>

	@Bean
	public FeignContext feignContext() {
		FeignContext context = new FeignContext();
		context.setConfigurations(this.configurations);
		return context;
	}

	@Configuration(proxyBeanMethods = false)
	@ConditionalOnClass(name = "feign.hystrix.HystrixFeign")
	protected static class HystrixFeignTargeterConfiguration {

		@Bean
		@ConditionalOnMissingBean
		public Targeter feignTargeter() {
			return new HystrixTargeter();
		}

	}


@Configuration(proxyBeanMethods = false)
class DefaultFeignLoadBalancedConfiguration {

	@Bean
	@ConditionalOnMissingBean
	public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
			SpringClientFactory clientFactory) {
		return new LoadBalancerFeignClient(new Client.Default(null, null), cachingFactory,
				clientFactory);
	}

}

1. 使用注解导入启动类

2. 启动类进行 对 FeignClient 注解 注册到Srping容器中

org.springframework.cloud.openfeign.FeignClientFactoryBean

 

3. FeignClientFactoryBean 实例化

FeignClientFactoryBean 实例化时，通过 FeignClientFactoryBean#getObject 来获取代理对象，handler： feign.ReflectiveFeign.FeignInvocationHandler

if (!StringUtils.hasText(this.url)) {
			if (!this.name.startsWith("http")) {
				this.url = "http://" + this.name;
			}
			else {
				this.url = this.name;
			}
			this.url += cleanPath();
			return (T) loadBalance(builder, context,
					new HardCodedTarget<>(this.type, this.name, this.url));
		}

1. 如果没有指定url，则 使用 name，如： http://your-service

 

static class FeignInvocationHandler implements InvocationHandler {

    private final Target target;
    private final Map<Method, MethodHandler> dispatch;

    FeignInvocationHandler(Target target, Map<Method, MethodHandler> dispatch) {
      this.target = checkNotNull(target, "target");
      this.dispatch = checkNotNull(dispatch, "dispatch for %s", target);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      if ("equals".equals(method.getName())) {
        try {
          Object otherHandler =
              args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
          return equals(otherHandler);
        } catch (IllegalArgumentException e) {
          return false;
        }
      } else if ("hashCode".equals(method.getName())) {
        return hashCode();
      } else if ("toString".equals(method.getName())) {
        return toString();
      }

      return dispatch.get(method).invoke(args);
    }

final class SynchronousMethodHandler implements MethodHandler {

 

  @Override
  public Object invoke(Object[] argv) throws Throwable {
    RequestTemplate template = buildTemplateFromArgs.create(argv);
    Options options = findOptions(argv);
    Retryer retryer = this.retryer.clone();
    while (true) {
      try {
        return executeAndDecode(template, options);
      } catch (RetryableException e) {
        try {
          retryer.continueOrPropagate(e);
        } catch (RetryableException th) {
          Throwable cause = th.getCause();
          if (propagationPolicy == UNWRAP && cause != null) {
            throw cause;
          } else {
            throw th;
          }
        }
        if (logLevel != Logger.Level.NONE) {
          logger.logRetry(metadata.configKey(), logLevel);
        }
        continue;
      }
    }
  }

 response = client.execute(request, options);

这个里的client 是在这里获取的，也就是 获取 容器中的 类型是 Clinet.class 的bean

Client client = getOptional(context, Client.class);

 public <T> T getInstance(String name, Class<T> type) {
        AnnotationConfigApplicationContext context = this.getContext(name);

        try {
            return context.getBean(type);
        } catch (NoSuchBeanDefinitionException var5) {
            return null;
        }
    }

这个bean 是自动注册上的：

@Configuration(proxyBeanMethods = false)
class DefaultFeignLoadBalancedConfiguration {

	@Bean
	@ConditionalOnMissingBean
	public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
			SpringClientFactory clientFactory) {
		return new LoadBalancerFeignClient(new Client.Default(null, null), cachingFactory,
				clientFactory);
	}

}

org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient

public class LoadBalancerFeignClient implements Client {

	@Override
	public Response execute(Request request, Request.Options options) throws IOException {
		try {
			URI asUri = URI.create(request.url());
			String clientName = asUri.getHost();
			URI uriWithoutHost = cleanUrl(request.url(), clientName);
			FeignLoadBalancer.RibbonRequest ribbonRequest = new FeignLoadBalancer.RibbonRequest(
					this.delegate, request, uriWithoutHost);

			IClientConfig requestConfig = getClientConfig(options, clientName);
			return lbClient(clientName)
					.executeWithLoadBalancer(ribbonRequest, requestConfig).toResponse();
		}
		catch (ClientException e) {
			IOException io = findIOException(e);
			if (io != null) {
				throw io;
			}
			throw new RuntimeException(e);
		}
	}

4. 接口请求时，走负责均衡器，从注册中心获取服务列表

通过 ribbon 进行负载均衡

如果使用的是nacos注册中心：

注册 nacos注册中心地址

更新serverList

如果引入了 spring-retry组件，会自动完成失败重试，故障转移。比如调用的Aserver失败，会自动切换到Bserver再次调用。