springcloudalibaba学习（六）OpenFeign初始化流程

目录

前言一、使用示例二、注册FeignClients三、实例化FeignClients四、FeignContext总结

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前言

在spring cloud alibaba 中使用OpenFeign，可以用来使用HTTP请求访问远程服务。

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一、使用示例

1、引入依赖

org.springframework.cloudspring-cloud-starter-openfeign3.0.0

2、启动类

加上注解@EnableFeignClients

@SpringBootApplication@EnableFeignClientspublic class CloudApplication {public static void main(String[] args) {SpringApplication.run(CloudApplication.class, args);System.out.println("started...");}}

3、创建服务api接口

用@FeignClient 注解标识，value = “server” 表示要访问的服务提供者的名称是server

@FeignClient(value = "server")@Componentpublic interface ServerApi { @GetMapping("/server/test/{id}") Map test(@PathVariable String id);}

4、Controller接口

@RestController@RequestMapping("/client")public class ClientController { @Autowired private ServerApi serverApi; @GetMapping("/test/{id}") public Map test(@PathVariable String id){ return serverApi.test(id); }}

二、注册FeignClients

1、@EnableFeignClients

在启动类上加上了注解@EnableFeignClients，该注解导入了配置类@import(FeignClientsRegistrar.class)

2、FeignClientsRegistrar

实现了 importBeanDefinitionRegistrar 接口，重写了 registerBeanDefinitions( ) 方法，
在配置类加载过程中，会回调该方法

loadBeanDefinitionsFromRegistrars(configClass.getimportBeanDefinitionRegistrars());

3、回调方法

FeignClientsRegistrar.java@Overridepublic void registerBeanDefinitions(Annotationmetadata metadata, BeanDefinitionRegistry registry) {//注册默认的配置类registerDefaultConfiguration(metadata, registry);//注册feign客户端 FeignClientsregisterFeignClients(metadata, registry);}

4、注册默认的配置类

private void registerDefaultConfiguration(Annotationmetadata metadata, BeanDefinitionRegistry registry) {//获取 @EnableFeignClients 注解信息Map defaultAttrs = metadata.getAnnotationAttributes(EnableFeignClients.class.getName(), true);if (defaultAttrs != null && defaultAttrs.containsKey("defaultConfiguration")) {String name;if (metadata.hasEnclosingClass()) {name = "default." + metadata.getEnclosingClassName();}else {name = "default." + metadata.getClassName();}//注册客户端配置类registerClientConfiguration(registry, name, defaultAttrs.get("defaultConfiguration"));}}

注册 FeignClientSpecification 类

private void registerClientConfiguration(BeanDefinitionRegistry registry, Object name, Object configuration) {BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(FeignClientSpecification.class);builder.addConstructorArgValue(name);builder.addConstructorArgValue(configuration);registry.registerBeanDefinition(name + "." + FeignClientSpecification.class.getSimpleName(),builder.getBeanDefinition());}

5、注册feign客户端

（1）registerFeignClients( )

public void registerFeignClients(Annotationmetadata metadata, BeanDefinitionRegistry registry) {linkedHashSet candidateComponents = new linkedHashSet<>();//1、获取 @EnableFeignClients 注解信息Map attrs = metadata.getAnnotationAttributes(EnableFeignClients.class.getName());//@FeignClient 注解类型过滤器AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(FeignClient.class);final Class<?>[] clients = attrs == null ? null : (Class<?>[]) attrs.get("clients");//2、获取包含@FeignClient 注解的接口if (clients == null || clients.length == 0) {//注解中没有指定要加载的 FeignClient 接口类，则进行扫描指定的包或当前处理的配置类所在的包//获取扫描器ClassPathScanningCandidateComponentProvider scanner = getScanner();scanner.setResourceLoader(this.resourceLoader);//设置注解类型过滤器scanner.addIncludeFilter(new AnnotationTypeFilter(FeignClient.class));//获取@FeignClient注解上的value/basePackages/basePackageClasses 或当前处理的配置类所在的包Set basePackages = getbasePackages(metadata);for (String basePackage : basePackages) {//找出包含@FeignClient 注解的接口candidateComponents.addAll(scanner.findCandidateComponents(basePackage));}}else {//注解中指定了要加载的 FeignClient 接口类for (Class<?> clazz : clients) {candidateComponents.add(new AnnotatedGenericBeanDefinition(clazz));}}//3、解析@FeignClient接口for (BeanDefinition candidateComponent : candidateComponents) {if (candidateComponent instanceof AnnotatedBeanDefinition) {// verify annotated class is an interfaceAnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;Annotationmetadata annotationmetadata = beanDefinition.getmetadata();Assert.isTrue(annotationmetadata.isInterface(), "@FeignClient can only be specified on an interface");Map attributes = annotationmetadata.getAnnotationAttributes(FeignClient.class.getCanonicalName());//@FeignClient制定的服务端的名称String name = getClientName(attributes);//根据服务端的名称注册FeignClientSpecification类registerClientConfiguration(registry, name, attributes.get("configuration"));//4、注册FeignClientregisterFeignClient(registry, annotationmetadata, attributes);}}}

6、注册FeignClient

private void registerFeignClient(BeanDefinitionRegistry registry, Annotationmetadata annotationmetadata,Map attributes) {String className = annotationmetadata.getClassName();//设置类型为 FeignClientFactoryBean，实现了FactoryBean