一. feign做了哪些事?
上面是一段feign的代码, 系统是如何通过feign, 将reduceStock方法转换成stock服务的接口调用的呢?
他做了两件事
1. 讲reduceStock方法中的入参拼接到请求地址
2. 讲请求的域名解析对应到指定的服务ip+端口号port----这一步使用到了ribbon进行服务器的选择
3. 然后调用http请求, 发送请求到stock服务----通过ribbon封装的restTemplate, 发送请求
二. feign的入口
通常我们使用feign会怎么使用呢?
第一步: 在启动类加上@EnableFeignClients注解
package com.lxl.order; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.cloud.client.discovery.EnableDiscoveryClient; import org.springframework.cloud.client.loadbalancer.LoadBalanced; import org.springframework.cloud.openfeign.EnableFeignClients; import org.springframework.context.annotation.Bean; import org.springframework.web.client.RestTemplate; @EnableDiscoveryClient @EnableFeignClients @SpringBootApplication public class OrderApplication { @LoadBalanced @Bean public RestTemplate getRestTemplate() { return new RestTemplate(); } public static void main(String[] args) { SpringApplication.run(OrderApplication.class, args); } }
第二步: 在对应的client类上加上@FeignClient注解
@FeignClient(name = "stock") public interface StockClient { @PostMapping("stock/reduce") String reduceStock(); /** * http://stock-service/stock/deduct/{productId}/{stockCount} * @param productId * @param stockCount * @return */ @PostMapping("reduce/count/{productId}/{stockCount}") String reduceStock(@PathVariable String productId, @PathVariable Integer stockCount); }
那么看源码, 我们就从这两个注解入手.
首先看第一个注解@EnableFeignClients
三. EnableFeignClients
通过@EnableFeignClients可以直接定位到feign的源码位置.
首先, 还是第一步: 看spring.factories
我们看到有一个FeignAutoConfiguration, 那么很有可能值就是feign的最开始的配置文件了. 我们来看看这个配置文件
3.1 FeignAutoConfiguration
这是一个配置类, 通常spring都是会通过一个AutoConfiguration来自动引入一些配置, 但是在feign的AutoConfiguration中没有引入太多的内容
/* * Copyright 2013-2020 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.cloud.openfeign; import java.util.ArrayList; import java.util.List; import java.util.Timer; import java.util.TimerTask; import java.util.concurrent.TimeUnit; import javax.annotation.PreDestroy; import feign.Client; import feign.Feign; import feign.httpclient.ApacheHttpClient; import feign.okhttp.OkHttpClient; import okhttp3.ConnectionPool; import org.apache.http.client.HttpClient; import org.apache.http.client.config.RequestConfig; import org.apache.http.config.RegistryBuilder; import org.apache.http.conn.HttpClientConnectionManager; import org.apache.http.impl.client.CloseableHttpClient; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.autoconfigure.condition.ConditionalOnClass; import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean; import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass; import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty; import org.springframework.boot.context.properties.EnableConfigurationProperties; import org.springframework.cloud.client.actuator.HasFeatures; import org.springframework.cloud.commons.httpclient.ApacheHttpClientConnectionManagerFactory; import org.springframework.cloud.commons.httpclient.ApacheHttpClientFactory; import org.springframework.cloud.commons.httpclient.OkHttpClientConnectionPoolFactory; import org.springframework.cloud.commons.httpclient.OkHttpClientFactory; import org.springframework.cloud.openfeign.support.DefaultGzipDecoderConfiguration; import org.springframework.cloud.openfeign.support.FeignHttpClientProperties; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; /** * @author Spencer Gibb * @author Julien Roy */ @Configuration(proxyBeanMethods = false) @ConditionalOnClass(Feign.class) @EnableConfigurationProperties({ FeignClientProperties.class, FeignHttpClientProperties.class }) @Import(DefaultGzipDecoderConfiguration.class) 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; } // 这个类定义的是和Hystrix有关的内容 @Configuration(proxyBeanMethods = false) @ConditionalOnClass(name = "feign.hystrix.HystrixFeign") protected static class HystrixFeignTargeterConfiguration { @Bean @ConditionalOnMissingBean public Targeter feignTargeter() { return new HystrixTargeter(); } } @Configuration(proxyBeanMethods = false) @ConditionalOnMissingClass("feign.hystrix.HystrixFeign") protected static class DefaultFeignTargeterConfiguration { @Bean @ConditionalOnMissingBean public Targeter feignTargeter() { return new DefaultTargeter(); } } // the following configuration is for alternate feign clients if // ribbon is not on the class path. // see corresponding configurations in FeignRibbonClientAutoConfiguration // for load balanced ribbon clients. // 这个也是有引入条件的, 如果使用了ApacheHttpClient, 那么使用这个配置内容 @Configuration(proxyBeanMethods = false) @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; @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 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(); } } } // 这个类的引入条件是在OkHttpClient上. 也就是如果你使用了OkHttpClient类,那么会执行这段内容 @Configuration(proxyBeanMethods = false) @ConditionalOnClass(OkHttpClient.class) @ConditionalOnMissingClass("com.netflix.loadbalancer.ILoadBalancer") @ConditionalOnMissingBean(okhttp3.OkHttpClient.class) @ConditionalOnProperty("feign.okhttp.enabled") 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(); Boolean disableSslValidation = httpClientProperties.isDisableSslValidation(); this.okHttpClient = httpClientFactory.createBuilder(disableSslValidation) .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(); } } @Bean @ConditionalOnMissingBean(Client.class) public Client feignClient(okhttp3.OkHttpClient client) { return new OkHttpClient(client); } } }
如上注解, 我们看到在这个FeignAutoConfiguration中没有引入太多的东西. 很多内容都是有条件使用的.
在feign中, 有一个最重要的注解, 就是下面这个注解
这是Spring 的注解了, 我们知道引入配置文件的方式有很多. 其中一个就是使用Import, 下面来具体看看FeignClientsRegistrar都做了那些事情
3.2 FeignClientsRegistrar
class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware {
这个类实现了ImportBeanDefinitionRegistrar, 那么就要重写他的一个方法registerBeanDefinitions
@Override public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) { registerDefaultConfiguration(metadata, registry); registerFeignClients(metadata, registry); }
1. registerDefaultConfiguration 看名字应该就能看出来, 这是一个引入默认的注册配置, 比如:我自定义在application中的配置, 在这时候读去出来, 进行加载
2. registerFeignClients: 这是一个主要的方法, 看名字就能猜出来, 这是注册feignClients, 我们在客户端自定义了很多带有@FeignClient的类, 就是扫描这些类.
public void registerFeignClients(AnnotationMetadata metadata, BeanDefinitionRegistry registry) { // 这里得到了一个扫描器 ClassPathScanningCandidateComponentProvider scanner = getScanner(); scanner.setResourceLoader(this.resourceLoader); Set<String> basePackages; // 扫描@EnableFeignClients注解,及其下面的属性,包和子包 Map<String, Object> attrs = metadata .getAnnotationAttributes(EnableFeignClients.class.getName()); // 过滤带有@FeignClient注解的包 AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter( FeignClient.class); final Class<?>[] clients = attrs == null ? null : (Class<?>[]) attrs.get("clients"); if (clients == null || clients.length == 0) { scanner.addIncludeFilter(annotationTypeFilter); basePackages = getBasePackages(metadata); } else { final Set<String> clientClasses = new HashSet<>(); basePackages = new HashSet<>(); for (Class<?> clazz : clients) { basePackages.add(ClassUtils.getPackageName(clazz)); clientClasses.add(clazz.getCanonicalName()); } AbstractClassTestingTypeFilter filter = new AbstractClassTestingTypeFilter() { @Override protected boolean match(ClassMetadata metadata) { String cleaned = metadata.getClassName().replaceAll("\\$", "."); return clientClasses.contains(cleaned); } }; scanner.addIncludeFilter( new AllTypeFilter(Arrays.asList(filter, annotationTypeFilter))); } for (String basePackage : basePackages) { Set<BeanDefinition> candidateComponents = scanner .findCandidateComponents(basePackage); for (BeanDefinition candidateComponent : candidateComponents) { if (candidateComponent instanceof AnnotatedBeanDefinition) { // verify annotated class is an interface AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent; AnnotationMetadata annotationMetadata = beanDefinition.getMetadata(); Assert.isTrue(annotationMetadata.isInterface(), "@FeignClient can only be specified on an interface"); Map<String, Object> attributes = annotationMetadata .getAnnotationAttributes( FeignClient.class.getCanonicalName()); String name = getClientName(attributes); registerClientConfiguration(registry, name, attributes.get("configuration")); // 这里就是最终将扫描的内容放入到容器中 registerFeignClient(registry, annotationMetadata, attributes); } } } }
1. 扫描器scanner扫描带有@EnableFiegnClients注解的包及其子包, 扫描带有@FeignClient注解的类, 使用过滤器扫描获得.
2. 把扫描的类放到spring容器里面
1. 使用spring的动态代理获取带有@FeignClient注解的类，然后解析方法，将参数和路径进行拼接获得完整的url.
2. 通过LoadBalancerFeignClient的execute方法解析上一步获得的url，将域名进行负载均衡后找到对应的ip：port. 然后进行http服务请求，后面就是ribbon的逻辑了，可以参考ribbon的实现
