SpringCloud @FeignClient注入找不到异常

怼烎@ 2024-03-31 08:35 82阅读 0赞

**前言**  
Springcloud中的服务间调用是通过Feign进行调用的，在调用方服务中，我们需要定义一些带有@FeignClient注解的接口类。并且在启动类上加上@EnableFeignClients注解。程序启动的时候，会检查是否有@EnableFeignClients注解，如果有该注解，则开启包扫描，扫描带有@FeignClient注解的接口。这里结合之前遇到的一个问题来和大家一起学习下@EnableFeignClients启动过程。

### 问题描述 ###

之前搭建一个简单demo的时候，启动之后总是报错

Field client1Feign in com.aiqinhai.client2.controller.Testrequired a bean of type
     'com.aiqinhai.client2.feignclient.Client1Feign' that could not be found.
    Action:
    Consider defining a bean of type 'com.aiqinhai.client2.feignclient.Client1Feign' in your configuration.
    Process finished with exit code 1

排查了一顿之后，发现启动上的@EnableFeignClients注解，没有指定basePackages包扫描路径。而且Client1Feign接口不是和启动类在同一目录下，所以启动的时候就会报上述错误。后来在@EnableFeignClients指定了扫描包路径就解决了。

@SpringBootApplication
    @EnableDiscoveryClient
    @EnableFeignClients(basePackages = {
        "com.aiqinhai.client2.feignclient"})
    public class Client2Application {
        
        public static void main(String[] args) {
        
            SpringApplication.run(Client2Application.class, args);
        }
    }

问题确实解决了，但是我们还是需要了解服务启动的时候，@EnableFeignClients注解干了哪些事。

### 刨根@EnableFeignClients ###

想了解清楚这个注解的作用，最好的方式就是看看注解的源码。点进去之后，可以看到

/**
     * 扫描注解@FeignClient标注的接口
     */
    @Retention(RetentionPolicy.RUNTIME)
    @Target({
        ElementType.TYPE})
    @Documented
    @Import(FeignClientsRegistrar.class)
    public @interface EnableFeignClients {
        
    	//同basePackages
    	String[] value() default {
        };
            //扫描的package.
    	String[] basePackages() default {
        };
    	//feigin client全局配置，默认配置在FeignClientsConfiguration类中
    	Class<?>[] defaultConfiguration() default {
        };
    	//@FeignClient注解的接口，如果指定了该属性，则关闭扫描。
    	Class<?>[] clients() default {
        };
    }

可以看到，注解中import了FeignClientsRegistrar类，我们进去看看，可以看到包扫描的逻辑就是在FeignClientsRegistrar中实现的，会扫描所有的.class文件，过滤出@FeignClient标注的接口，然后通过BeanDefinitionBuilder生成FeignClientFactoryBean对象，注入到IOC容器中。具体代码如下

class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar,
    		ResourceLoaderAware, EnvironmentAware {
        
    	//包扫描方法入口
    	@Override
    	public void registerBeanDefinitions(AnnotationMetadata metadata,
    			BeanDefinitionRegistry registry) {
        
    		//注册默认配置bean到ioc
    		registerDefaultConfiguration(metadata, registry);
    		//注册@FeignClients标注的接口bean,为其生成动态代理
    		registerFeignClients(metadata, registry);
    	}
    	private void registerDefaultConfiguration(AnnotationMetadata metadata,
    			BeanDefinitionRegistry registry) {
        
    		//获取@EnableFeignClients注解属性
    		Map<String, Object> 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@EnableFeignClients defaultConfiguration 类中定义的bean到ioc
    			registerClientConfiguration(registry, name,
    					defaultAttrs.get("defaultConfiguration"));
    		}
    	}
    	public void registerFeignClients(AnnotationMetadata metadata,
    			BeanDefinitionRegistry registry) {
        
    		//spring 扫描工具类
    		ClassPathScanningCandidateComponentProvider scanner = getScanner();
    		scanner.setResourceLoader(this.resourceLoader);
            //待扫描的包
    		Set<String> basePackages;
            //@EnableFeignClients注解属性
    		Map<String, Object> attrs = metadata
    				.getAnnotationAttributes(EnableFeignClients.class.getName());
    		//@FeignClient注解过滤器，只扫描@FeignClient注解标注的接口
    		AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(
    				FeignClient.class);
    		//解析@EnableFeignClient 属性clients
    		final Class<?>[] clients = attrs == null ? null
    				: (Class<?>[]) attrs.get("clients");
    		//如果@EnableFeignClient没有指定clients,则开启包扫描，否则关闭扫描，使用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) {
        
    		    //从类路径下的所有.class文件中扫描@FeignClient注解的接口
    			Set<BeanDefinition> candidateComponents = scanner
    					.findCandidateComponents(basePackage);
    			for (BeanDefinition candidateComponent : candidateComponents) {
        
    				if (candidateComponent instanceof AnnotatedBeanDefinition) {
        
    					// verify annotated class is an interface
    					AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;
    					//获取注解
    					AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();
    					//@FeignClient注解必须应用在接口上，否则抛出异常。
    					Assert.isTrue(annotationMetadata.isInterface(),
    							"@FeignClient can only be specified on an interface");
                            //获取FeignClient注解属性
    					Map<String, Object> attributes = annotationMetadata
    							.getAnnotationAttributes(
    									FeignClient.class.getCanonicalName());
                            //服务名称
    					String name = getClientName(attributes);
    					//注册configuration中指定的bean
    					registerClientConfiguration(registry, name,
    							attributes.get("configuration"));
    					//生成FeignClient bean,并注册到ioc
    					registerFeignClient(registry, annotationMetadata, attributes);
    				}
    			}
    		}
    	}
     
        //生成bean,注入到IOC容器
    	private void registerFeignClient(BeanDefinitionRegistry registry,
    			AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
        
    		// feignclient类名称
    		String className = annotationMetadata.getClassName();
    		BeanDefinitionBuilder definition = BeanDefinitionBuilder
    				.genericBeanDefinition(FeignClientFactoryBean.class);
    		validate(attributes);
    		definition.addPropertyValue("url", getUrl(attributes));
    		definition.addPropertyValue("path", getPath(attributes));
    		String name = getName(attributes);
    		definition.addPropertyValue("name", name);
    		definition.addPropertyValue("type", className);
    		definition.addPropertyValue("decode404", attributes.get("decode404"));
    		definition.addPropertyValue("fallback", attributes.get("fallback"));
    		definition.addPropertyValue("fallbackFactory", attributes.get("fallbackFactory"));
    		definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
     
    		String alias = name + "FeignClient";
    		AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
     
    		boolean primary = (Boolean)attributes.get("primary"); // has a default, won't be null
    		beanDefinition.setPrimary(primary);
    		String qualifier = getQualifier(attributes);
    		if (StringUtils.hasText(qualifier)) {
        
    			alias = qualifier;
    		}
    		BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,
    				new String[] {
         alias });
    		//注册到ioc
    		BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
    	}
    }

从上面的代码中，可以看到@EnableFeignClients的包扫描逻辑。

原文地址：https://aiqinhai.blog.csdn.net/article/details/102328066