目录
FeignRibbonClientAutoConfiguration
1、FeignHttpClientProperties加载配置项
2、CachingSpringLoadBalancerFactory
1、HttpClientFeignLoadBalancedConfiguration
2、OkHttpFeignLoadBalancedConfiguration
3、DefaultFeignLoadBalancedConfiguration
随着Spring Boot项目的启动，会进行自动装配加载，当我们添加了spring-cloud-starter-openfeign启动maven依赖后，则会加载自动装配项如下：
则会自动装配FeignRibbonClientAutoConfiguration和FeignAutoConfiguration类型，但是在FeignRibbonClientAutoConfiguration的类注解上则有@AutoConfigureBefore(FeignAutoConfiguration.class)，即优于FeignAutoConfiguration进行加载。
FeignRibbonClientAutoConfiguration
// 1、ILoadBalancer和Feign类存在才加载该Bean FeignRibbonClientAutoConfiguration @ConditionalOnClass({ ILoadBalancer.class, Feign.class }) @Configuration // 2、当前的FeignRibbonClientAutoConfiguration先于FeignAutoConfiguration加载 @AutoConfigureBefore(FeignAutoConfiguration.class) // 3、加载配置FeignHttpClientProperties的属性 @EnableConfigurationProperties({ FeignHttpClientProperties.class }) // 4、有顺序的加载HttpClient、okhttp类型（前提【都】是引入了包和启动配置）、最后优先级是加载默认项，后面详细分析该部分 @Import({ HttpClientFeignLoadBalancedConfiguration.class, OkHttpFeignLoadBalancedConfiguration.class, DefaultFeignLoadBalancedConfiguration.class }) public class FeignRibbonClientAutoConfiguration { // 5、加载CachingSpringLoadBalancerFactory类型Bean，前提是没有类RetryTemplate，该需要单独引入Spring-retry的maven依赖 @Bean @Primary @ConditionalOnMissingBean @ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate") public CachingSpringLoadBalancerFactory cachingLBClientFactory( SpringClientFactory factory) { return new CachingSpringLoadBalancerFactory(factory); } // 6、加载CachingSpringLoadBalancerFactory类型Bean，前提是存在类RetryTemplate，该需要单独引入Spring-retry的maven依赖 @Bean @Primary @ConditionalOnMissingBean @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate") public CachingSpringLoadBalancerFactory retryabeCachingLBClientFactory( SpringClientFactory factory, LoadBalancedRetryFactory retryFactory) { return new CachingSpringLoadBalancerFactory(factory, retryFactory); } // 7、加载全局的默认@FeignClient的连接和读取超时配置 @Bean @ConditionalOnMissingBean public Request.Options feignRequestOptions() { return LoadBalancerFeignClient.DEFAULT_OPTIONS; } }1、ILoadBalancer和Feign类存在才加载该Bean FeignRibbonClientAutoConfiguration 2、当前的FeignRibbonClientAutoConfiguration先于FeignAutoConfiguration加载 3、加载配置FeignHttpClientProperties的属性 4、有顺序的加载HttpClient、okhttp类型（前提【都】是引入了包和启动配置）、优先级最低的是加载默认项 5、加载CachingSpringLoadBalancerFactory类型Bean，前提是没有类RetryTemplate，该需要单独引入Spring-retry的maven依赖 6、加载CachingSpringLoadBalancerFactory类型Bean，前提是存在类RetryTemplate，该需要单独引入Spring-retry的maven依赖 7、加载全局的默认@FeignClient的连接和读取超时配置1、FeignHttpClientProperties加载配置项
@ConfigurationProperties(prefix = "feign.httpclient") public class FeignHttpClientProperties { }加载http client相关的配置项，需要配置后面的HttpClientFeignLoadBalancedConfiguration进行分析。
2、CachingSpringLoadBalancerFactory
缓存的负载均衡调用工厂非常重要，他提供了两个构造函数，SpringClientFactory类型，以及看我们是否添加了Spring-Retry的maven依赖，有则可以对服务的调用增加失败重试机制，否则直接走降级。所以当前使用的是构造函数依赖注入的方式，则需要关注在其他地方注入的SpringClientFactory类型的Bean。使用的地方后续服务调用时再分析。
3、配置默认的@FeignClient的连接和调用超时时间
@Bean @ConditionalOnMissingBean public Request.Options feignRequestOptions() { return LoadBalancerFeignClient.DEFAULT_OPTIONS; }如果其他地方没有注入该值，即我们没有使用yml、properties设置超时时间则会为服务调用设置超时时间，并且FeignClientFactoryBean#getObject过程会发现，配置项适用于所有的@FeignClient项。
public class LoadBalancerFeignClient implements Client { static final Request.Options DEFAULT_OPTIONS = new Request.Options(); public static class Options { private final int connectTimeoutMillis; private final int readTimeoutMillis; private final boolean followRedirects; public Options(int connectTimeoutMillis, int readTimeoutMillis, boolean followRedirects) { this.connectTimeoutMillis = connectTimeoutMillis; this.readTimeoutMillis = readTimeoutMillis; this.followRedirects = followRedirects; } public Options(int connectTimeoutMillis, int readTimeoutMillis) { this(connectTimeoutMillis, readTimeoutMillis, true); } public Options() { this(10 * 1000, 60 * 1000); } }所以默认的链接超时是1秒，读取超时是60秒
Feign客户端实现
先看看Feign的Client【客户端】即真正调用远程服务的接口：
public interface Client { Response execute(Request request, Options options) throws IOException; }定义了真的调用的Http请求的过程，其中Options类型，上面已经见过了，配置了超时时间。其子类按照优先级有：
ApacheHttpClient：优先级最高使用的是Apache的HttpClient线程池实现，前提是引入feign-httpclient依赖
OkHttpClient：使用OkHttp线程池实现，需要引入feign-okhttp依赖
Client.Default：使用默认的HttpURLConnnection连接池，但是性能比较低，特别是访问路径中存在{}占位符等
LoadBalancerFeignClient：使用装饰器模式，对上面的类型进行包装，因为不论是否那种方式的连接池，最后调用服务时都需要负载均衡策略
还是从上面的注解开始：
@Import({ HttpClientFeignLoadBalancedConfiguration.class, OkHttpFeignLoadBalancedConfiguration.class, DefaultFeignLoadBalancedConfiguration.class })1、HttpClientFeignLoadBalancedConfiguration
对应上面的ApacheHttpClient类型客户端，需要引入maven依赖，如：
<dependency> <groupId>io.github.openfeign</groupId> <artifactId>feign-httpclient</artifactId> <version>9.5.0</version> </dependency>@Configuration @ConditionalOnClass(ApacheHttpClient.class) @ConditionalOnProperty(value = "feign.httpclient.enabled", matchIfMissing = true) class HttpClientFeignLoadBalancedConfiguration { @Bean @ConditionalOnMissingBean(Client.class) public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory, SpringClientFactory clientFactory, HttpClient httpClient) { ApacheHttpClient delegate = new ApacheHttpClient(httpClient); return new LoadBalancerFeignClient(delegate, cachingFactory, clientFactory); } @Configuration @ConditionalOnMissingBean(CloseableHttpClient.class) protected static class HttpClientFeignConfiguration { private final Timer connectionManagerTimer = new Timer( "FeignApacheHttpClientConfiguration.connectionManagerTimer", true); private CloseableHttpClient httpClient; @Autowired(required = false) private RegistryBuilder registryBuilder; @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() { @Override public void run() { connectionManager.closeExpiredConnections(); } }, 30000, httpClientProperties.getConnectionTimerRepeat()); return connectionManager; } @Bean @ConditionalOnProperty(value = "feign.compression.response.enabled", havingValue = "true") public CloseableHttpClient customHttpClient( HttpClientConnectionManager httpClientConnectionManager, FeignHttpClientProperties httpClientProperties) { HttpClientBuilder builder = HttpClientBuilder.create() .disableCookieManagement().useSystemProperties(); this.httpClient = createClient(builder, httpClientConnectionManager, httpClientProperties); return this.httpClient; } @Bean @ConditionalOnProperty(value = "feign.compression.response.enabled", havingValue = "false", matchIfMissing = true) public CloseableHttpClient httpClient(ApacheHttpClientFactory httpClientFactory, HttpClientConnectionManager httpClientConnectionManager, FeignHttpClientProperties httpClientProperties) { this.httpClient = createClient(httpClientFactory.createBuilder(), httpClientConnectionManager, httpClientProperties); return this.httpClient; } private CloseableHttpClient createClient(HttpClientBuilder builder, HttpClientConnectionManager httpClientConnectionManager, FeignHttpClientProperties httpClientProperties) { RequestConfig defaultRequestConfig = RequestConfig.custom() .setConnectTimeout(httpClientProperties.getConnectionTimeout()) .setRedirectsEnabled(httpClientProperties.isFollowRedirects()) .build(); CloseableHttpClient httpClient = builder .setDefaultRequestConfig(defaultRequestConfig) .setConnectionManager(httpClientConnectionManager).build(); return httpClient; } @PreDestroy public void destroy() throws Exception { this.connectionManagerTimer.cancel(); if (this.httpClient != null) { this.httpClient.close(); } } } }1、不仅需要引入上面的maven依赖，才@ConditionalOnClass(ApacheHttpClient.class)能注入
2、需要配置属性feign.httpclient.enabled
@ConditionalOnProperty(value = "feign.httpclient.enabled", matchIfMissing = true)
3、构造器依赖于上面注入的CachingSpringLoadBalancerFactory，SpringClientFactory、HttpClient类型Bean，注入返回装饰ApacheHttpClient类型的LoadBalancerFeignClient客户端
4、创建连接器管理器HttpClientConnectionManager，虽然设置了一些超市等参数信息，并且使用到了上面从配置文件中加载的FeignHttpClientProperties进行构造依赖注入，但是我们看看真正的管理器实现类为PoolingHttpClientConnectionManager
public PoolingHttpClientConnectionManager( final HttpClientConnectionOperator httpClientConnectionOperator, final HttpConnectionFactory<HttpRoute, ManagedHttpClientConnection> connFactory, final long timeToLive, final TimeUnit timeUnit) { super(); this.configData = new ConfigData(); this.pool = new CPool(new InternalConnectionFactory( this.configData, connFactory), 2, 20, timeToLive, timeUnit); this.pool.setValidateAfterInactivity(2000); this.connectionOperator = Args.notNull(httpClientConnectionOperator, "HttpClientConnectionOperator"); this.isShutDown = new AtomicBoolean(false); }那么底层真实的线程池参数，则不满足并发量比较高的情况，所以一般建议我们自己显示进行设置，也方便后续进行参数修改，一般需要上线后与其他使用自定义线程池一样进行压测，设置最合理的参数信息。
@Bean(destroyMethod = "close") public CloseableHttpClient httpClient() { PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager(); connectionManager.setMaxTotal(400); connectionManager.setDefaultMaxPerRoute(100); RequestConfig requestConfig = RequestConfig.custom().setConnectionRequestTimeout(2000)//从连接池获取连接等待超时时间 .setConnectTimeout(2000)//请求超时时间 .setSocketTimeout(15000)//等待服务响应超时时间 .build(); HttpClientBuilder httpClientBuilder = HttpClientBuilder.create().setConnectionManager(connectionManager) .setDefaultRequestConfig(requestConfig) //自定义重试策略，针对502和503重试一次 .setServiceUnavailableRetryStrategy(new CustomizedServiceUnavailableRetryStrategy()) .evictExpiredConnections(); return httpClientBuilder.build(); }2、OkHttpFeignLoadBalancedConfiguration
对应上面的OkHttpClient类型客户端，需要引入maven依赖，如：
<dependency> <groupId>io.github.openfeign</groupId> <artifactId>feign-okhttp</artifactId> <version>10.2.0</version> </dependency>@Configuration @ConditionalOnClass(OkHttpClient.class) @ConditionalOnProperty("feign.okhttp.enabled") class OkHttpFeignLoadBalancedConfiguration { @Bean @ConditionalOnMissingBean(Client.class) public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory, SpringClientFactory clientFactory, okhttp3.OkHttpClient okHttpClient) { OkHttpClient delegate = new OkHttpClient(okHttpClient); return new LoadBalancerFeignClient(delegate, cachingFactory, clientFactory); } @Configuration @ConditionalOnMissingBean(okhttp3.OkHttpClient.class) protected static class OkHttpFeignConfiguration { private okhttp3.OkHttpClient okHttpClient; @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(); this.okHttpClient = httpClientFactory .createBuilder(httpClientProperties.isDisableSslValidation()) .connectTimeout(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(); } } } }1、不仅需要引入上面的maven依赖，才@ConditionalOnClass(OkHttpClient.class)能注入
2、需要配置属性feign.okhttp.enabled
@ConditionalOnProperty("feign.okhttp.enabled")
3、构造器依赖于上面注入的CachingSpringLoadBalancerFactory，SpringClientFactory、HttpClient类型Bean，注入返回装饰OkHttpClient类型的LoadBalancerFeignClient客户端
4、构造器依赖注入返回连接器ConnectionPool类型，也使用到了上面配置的FeignHttpClientProperties属性，还有依赖到了OkHttpClientConnectionPoolFactory类型，全局查找发现是从spring-cloud-commons包中的HttpClientConfiguration中进行配置的，返回了DefaultOkHttpClientConnectionPoolFactory类型。
public class DefaultOkHttpClientConnectionPoolFactory implements OkHttpClientConnectionPoolFactory { @Override public ConnectionPool create(int maxIdleConnections, long keepAliveDuration, TimeUnit timeUnit) { return new ConnectionPool(maxIdleConnections, keepAliveDuration, timeUnit); } }直接new的对象，设置了连接的最大数，超时等参数，但是线程池是对象中默认写死的，入下：
public final class ConnectionPool { private static final Executor executor = new ThreadPoolExecutor(0 /* corePoolSize */, Integer.MAX_VALUE /* maximumPoolSize */, 60L /* keepAliveTime */, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp ConnectionPool", true)); }直接使用了juc原生的线程池，核心线程为0，最大线程为Integer最大值，并且使用了无界队列SynchronousQueue【入队需要有其他任务出队】，即maxIdleConnections最大连接数参数就很关键了，需要小心参数。
3、DefaultFeignLoadBalancedConfiguration
不满足上面的条件，则会注入默认的Feign Client，如下：
@Configuration class DefaultFeignLoadBalancedConfiguration { @Bean @ConditionalOnMissingBean public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory, SpringClientFactory clientFactory) { return new LoadBalancerFeignClient(new Client.Default(null, null), cachingFactory, clientFactory); } }FeignAutoConfiguration
由于上面的优先级高于该自动装配项，大多的装配以上面为准，但是这里装配了两个比较重要的Bean：HasFeatures和FeignContext，特别是FeignContext会在后面FeignClientFactoryBean#getObject中使用到。
public class FeignAutoConfiguration { @Autowired(required = false) private List<FeignClientSpecification> configurations = new ArrayList<>(); @Bean public HasFeatures feignFeature() { return HasFeatures.namedFeature("Feign", Feign.class); } @Bean public FeignContext feignContext() { FeignContext context = new FeignContext(); context.setConfigurations(this.configurations); return context; } }
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