Client组件是一个非常重要的组件，Feign终发送request请求以及接收response响应，都是由Client组件完成的，其中Client的实现类，只要有Client.Default，该类由HttpURLConnnection实现网络请求，另外还支持HttpClient、Okhttp.

首先来看以下在FeignRibbonClient的自动配置类，FeignRibbonClientAutoConfiguration ，主要在工程启动的时候注入一些bean,其代码如下

@ConditionalOnClass({ ILoadBalancer.class, Feign.class })
@Configuration
@AutoConfigureBefore(FeignAutoConfiguration.class)
public class FeignRibbonClientAutoConfiguration {

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

}

在缺失配置feignClient的情况下，会自动注入new Client.Default(),跟踪Client.Default()源码，它使用的网络请求框架为HttpURLConnection，代码如下：

@Override
public Response execute(Request request, Options options) throws IOException {
HttpURLConnection connection = convertAndSend(request, options);
return convertResponse(connection).toBuilder().request(request).build();
}


怎么在feign中使用HttpClient，查看FeignRibbonClientAutoConfiguration的源码

@ConditionalOnClass({ ILoadBalancer.class, Feign.class })
@Configuration
@AutoConfigureBefore(FeignAutoConfiguration.class)
public class FeignRibbonClientAutoConfiguration {
...//省略代码

@Configuration
@ConditionalOnClass(ApacheHttpClient.class)
@ConditionalOnProperty(value = "feign.httpclient.enabled", matchIfMissing = true)
protected static class HttpClientFeignLoadBalancedConfiguration {

@Autowired(required = false)
private HttpClient httpClient;

@Bean
@ConditionalOnMissingBean(Client.class)
public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
SpringClientFactory clientFactory) {
ApacheHttpClient delegate;
if (this.httpClient != null) {
delegate = new ApacheHttpClient(this.httpClient);
}
else {
delegate = new ApacheHttpClient();
}
return new LoadBalancerFeignClient(delegate, cachingFactory, clientFactory);
}
}

...//省略代码
}

从代码@ConditionalOnClass(ApacheHttpClient.class)注解可知道，只需要在pom文件加上HttpClient的classpath就行了，另外需要在配置文件上加上feign.httpclient.enabled为true，从 @ConditionalOnProperty注解可知，这个可以不写，在默认的情况下就为true.

在pom文件加上：

<dependency>
<groupId>com.netflix.feign</groupId>
<artifactId>feign-httpclient</artifactId>
<version>RELEASE</version>
</dependency>


同理，如果想要feign使用Okhttp，则只需要在pom文件上加上feign-okhttp的依赖：

<dependency>
<groupId>com.netflix.feign</groupId>
<artifactId>feign-okhttp</artifactId>
<version>RELEASE</version>
</dependency>

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