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一文详解Spring Cloud Feign重试机制

前言

Feign组件默认使用Ribbon的重试机制并增加了根据状态码判断重试机制，默认情况下是不启用的。Feign使用的是Spring Retry组件，需要引入依赖才能启用。

一、POM引入Spring Retry

<dependency>
        <groupId>org.springframework.retry</groupId>
        <artifactId>spring-retry</artifactId>
  </dependency>

二、配置文件

eureka-client:
   ribbon:
      MaxAutoRetries: 1
      MaxAutoRetriesNextServer: 1
      retryableStatusCodes: 500,404 
      OkToRetryOnAllOperations: true 
      NFLoadBalancerRuleClassName: com.netflix.loadbalancer.AvailabilityFilteringRule #负载均衡规则

eureka-client 是自己的serverId， MaxAutoRetries 同一台服务器上的最大重试次数（不包括第一次尝试）， MaxAutoRetriesNextServer 要重试的下一个服务器的最大数量（不包括第一个服务器）， retryableStatusCodes 可以根据接口返回的状态码判断是否重试其他服务， OkToRetryOnAllOperations 只对所有的超时请求重试

注意： Ribbon的重试机制只有对GET请求或者设置了OkToRetryOnAllOperations生效详情请查看源码：

public class RibbonLoadBalancedRetryPolicy implements LoadBalancedRetryPolicy {
    ...
        public Boolean canRetry(LoadBalancedRetryContext context) {
        HttpMethod method = context.getRequest().getMethod();
        return HttpMethod.GET == method || lbContext.isOkToRetryOnAllOperations();
    }
    ...
}

Feign对返回状态码做了重试判断RetryableFeignLoadBalancer

public class RetryableFeignLoadBalancer extends FeignLoadBalancer
    implements ServiceInstanceChooser {
    ...
        [@Override](https://my.oschina.net/u/1162528)
    public RibbonResponse execute(final RibbonRequest request,
                IClientConfig configOverride) throws IOException {
        ...
                if (retryPolicy != null
                                && retryPolicy.retryableStatusCode(response.status())) {
            byte[] byteArray = response.body() == null ? new byte[] {}
                                        : StreamUtils
                                                .copyToByteArray(response.body().asInputStream());
            response.close();
            throw new RibbonResponseStatusCodeException(
                                        RetryableFeignLoadBalancer.this.clientName, response,
                                        byteArray, request.getUri());
        }
        ...
    }
    ...
}

重试机制用的是Spring Retry组件当抛出异常时进行重试！

GET请求指的是feign client 请求其他client时声明的那个interface中mapping注解类型，RequestMapping不设置method默认为GET请求

@FeignClient("stores")
public interface StoreClient {
    @RequestMapping(method = RequestMethod.GET, value = "/stores")
        List<Store> getStores();
    @RequestMapping(method = RequestMethod.POST, value = "/stores/{storeId}", consumes = "application/json")
        Store update(@PathVariable("storeId") long storeId, Store store);
}