监控Feign调用metrics

metrics 支持okhttp的监控，故将feign的底层换成okhttp，即可加入监控

配置类
```
@Configuration
public class FeignConfig {

@Configuration
    @ConditionalOnClass(OkHttpClient.class)
    @ConditionalOnMissingClass("com.netflix.loadbalancer.ILoadBalancer")
    @ConditionalOnProperty("feign.okhttp.enabled")
    protected static class OkHttpFeignConfiguration {

private okhttp3.OkHttpClient okHttpClient;

@Bean
        @ConditionalOnMissingBean(ConnectionPool.class)
        public ConnectionPool httpClientConnectionPool(
                FeignHttpClientProperties httpClientProperties,
                OkHttpClientConnectionPoolFactory connectionPoolFactory) {
            int maxTotalConnections = httpClientProperties.getMaxConnections();
            long timeToLive = httpClientProperties.getTimeToLive();
            TimeUnit ttlUnit = httpClientProperties.getTimeToLiveUnit();
            return connectionPoolFactory.create(maxTotalConnections, timeToLive, ttlUnit);
        }

@Bean
        public okhttp3.OkHttpClient client(OkHttpClientFactory httpClientFactory,
                                           ConnectionPool connectionPool,
                                           FeignHttpClientProperties httpClientProperties,
                                           OkHttpMetricsEventListener okHttpMetricsEventListener) {
            this.okHttpClient = httpClientFactory.createBuilder(httpClientProperties.isDisableSslValidation())
                    .eventListener(okHttpMetricsEventListener)
					// 配置metrics监听器
                    .connectTimeout(httpClientProperties.getConnectionTimeout(), TimeUnit.MILLISECONDS)
                    .followRedirects(httpClientProperties.isFollowRedirects())
                    .connectionPool(connectionPool)
                    .build();
            return this.okHttpClient;
        }

@PreDestroy
        public void destroy() {
            if (this.okHttpClient != null) {
                this.okHttpClient.dispatcher().executorService().shutdown();
                this.okHttpClient.connectionPool().evictAll();
            }
        }

@Bean
        public OkHttpMetricsEventListener okHttpMetricsEventListener(MeterRegistry meterRegistry) {
            return  OkHttpMetricsEventListener.builder(meterRegistry, "ok")
					// 默认也支持URI_PATTERN header支持uri tag
                    .uriMapper(request -> request.url().encodedPath())
					// 这里可以指定自定义的tag
                    .tags(Collections.emptyList())
                    .build();
        }

@Bean
        @ConditionalOnMissingBean(Client.class)
        public Client feignClient(okhttp3.OkHttpClient client) {
            return new OkHttpClient(client);
        }

}
}
```

原文章作者: shiv
 原文章链接: http://wvht2y.coding-pages.com/2020/02/22/jian-kong-feign-diao-yong-metrics/