Feign-使用HttpClient和OkHttp

        在Feign中，Client是一个非常重要的组件，Feign最终发送Request请求以及接收Response响应都是由Client组件来完成的。Client在Feign源码中是一个接口，在默认情况下，Client的实现类是Client.Default。Client.Default是由HttpURLConnection来实现网络请求的。另外,Client还支持HttpClient和OkHttp来进行网络请求。

        首先查看FeignRibbonClient的自动配置类FeignRibbonClientAutoConfiguration，该类在程序启动的时候注入一些Bean，其中注入了一个BeanName为feignClient的Client类型的Bean。在省缺配置BeanName为FeignClient的Bean的情况下，会自动注入Client.Default这个对象，跟踪Client.Default源码,Client.Default使用的网络请求框架是HttpURLConnection，代码如下：

public static class Default implements Client {
        private final SSLSocketFactory sslContextFactory;
        private final HostnameVerifier hostnameVerifier;
 
        public Default(SSLSocketFactory sslContextFactory, HostnameVerifier hostnameVerifier) {
            this.sslContextFactory = sslContextFactory;
            this.hostnameVerifier = hostnameVerifier;
        }
 
        public Response execute(Request request, Options options) throws IOException {
            HttpURLConnection connection = this.convertAndSend(request, options);
            return this.convertResponse(connection, request);
        }
        
        ......//代码省略
}

        这种情况下，由于缺乏连接池的支持，在达到一定流量的后服务肯定会出问题 。    

使用HttpClient

        那么如何在Feign中使用HttpClient的框架呢？我们查看FeignAutoConfiguration.HttpClientFeignConfiguration的源码：

    @Configuration
    @ConditionalOnClass({ApacheHttpClient.class})
    @ConditionalOnMissingClass({"com.netflix.loadbalancer.ILoadBalancer"})
    @ConditionalOnMissingBean({CloseableHttpClient.class})
    @ConditionalOnProperty(
        value = {"feign.httpclient.enabled"},
        matchIfMissing = true
    )
    protected static class HttpClientFeignConfiguration {
        private final Timer connectionManagerTimer = new Timer("FeignApacheHttpClientConfiguration.connectionManagerTimer", true);
        @Autowired(
            required = false
        )
        private RegistryBuilder registryBuilder;
        private CloseableHttpClient httpClient;
 
        protected HttpClientFeignConfiguration() {
        }
 
        @Bean
        @ConditionalOnMissingBean({HttpClientConnectionManager.class})
        public HttpClientConnectionManager connectionManager(ApacheHttpClientConnectionManagerFactory connectionManagerFactory, FeignHttpClientProperties httpClientProperties) {
            final HttpClientConnectionManager connectionManager = connectionManagerFactory.newConnectionManager(httpClientProperties.isDisableSslValidation(), httpClientProperties.getMaxConnections(), httpClientProperties.getMaxConnectionsPerRoute(), httpClientProperties.getTimeToLive(), httpClientProperties.getTimeToLiveUnit(), this.registryBuilder);
            this.connectionManagerTimer.schedule(new TimerTask() {
                public void run() {
                    connectionManager.closeExpiredConnections();
                }
            }, 30000L, (long)httpClientProperties.getConnectionTimerRepeat());
            return connectionManager;
        }
 
        @Bean
        public CloseableHttpClient httpClient(ApacheHttpClientFactory httpClientFactory, HttpClientConnectionManager httpClientConnectionManager, FeignHttpClientProperties httpClientProperties) {
            RequestConfig defaultRequestConfig = RequestConfig.custom().setConnectTimeout(httpClientProperties.getConnectionTimeout()).setRedirectsEnabled(httpClientProperties.isFollowRedirects()).build();
            this.httpClient = httpClientFactory.createBuilder().setConnectionManager(httpClientConnectionManager).setDefaultRequestConfig(defaultRequestConfig).build();
            return this.httpClient;
        }
 
        @Bean
        @ConditionalOnMissingBean({Client.class})
        public Client feignClient(HttpClient httpClient) {
            return new ApacheHttpClient(httpClient);
        }
 
        @PreDestroy
        public void destroy() throws Exception {
            this.connectionManagerTimer.cancel();
            if (this.httpClient != null) {
                this.httpClient.close();
            }
 
        }
    }

        从代码@ConditionalOnClass({ApacheHttpClient.class})注解可知，只需要在pom文件上加上HttpClient依赖即可。另外需要在配置文件中配置feign.httpclient.enabled为true，从@ConditionalOnProperty注解可知，这个配置可以不写，因为在默认情况下就为true:

<dependency>
    <groupId>io.github.openfeign</groupId>
    <artifactId>feign-httpclient</artifactId>
    <version>9.4.0</version>
</dependency>

 

使用OkHttp

       查看FeignAutoConfiguration.HttpClientFeignConfiguration的源码：

    @Configuration
    @ConditionalOnClass({OkHttpClient.class})
    @ConditionalOnMissingClass({"com.netflix.loadbalancer.ILoadBalancer"})
    @ConditionalOnMissingBean({okhttp3.OkHttpClient.class})
    @ConditionalOnProperty({"feign.okhttp.enabled"})
    protected static class OkHttpFeignConfiguration {
        private okhttp3.OkHttpClient okHttpClient;
 
        protected OkHttpFeignConfiguration() {
        }
 
        @Bean
        @ConditionalOnMissingBean({ConnectionPool.class})
        public ConnectionPool httpClientConnectionPool(FeignHttpClientProperties httpClientProperties, OkHttpClientConnectionPoolFactory connectionPoolFactory) {
            Integer 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) {
            Boolean followRedirects = httpClientProperties.isFollowRedirects();
            Integer connectTimeout = httpClientProperties.getConnectionTimeout();
            Boolean disableSslValidation = httpClientProperties.isDisableSslValidation();
            this.okHttpClient = httpClientFactory.createBuilder(disableSslValidation).connectTimeout((long)connectTimeout, TimeUnit.MILLISECONDS).followRedirects(followRedirects).connectionPool(connectionPool).build();
            return this.okHttpClient;
        }
 
        @PreDestroy
        public void destroy() {
            if (this.okHttpClient != null) {
                this.okHttpClient.dispatcher().executorService().shutdown();
                this.okHttpClient.connectionPool().evictAll();
            }
 
        }
 
        @Bean
        @ConditionalOnMissingBean({Client.class})
        public Client feignClient(okhttp3.OkHttpClient client) {
            return new OkHttpClient(client);
        }
    }

       同理，如果想要在Feign中使用OkHttp作为网络请求框架，则只需要在pom文件中加上feign-okhttp的依赖，代码如下：

<dependency>
    <groupId>io.github.openfeign</groupId>
    <artifactId>feign-okhttp</artifactId>
    <version>10.2.0</version>
</dependency>