Feign自动装配原理

Java学习录

发布于 2019-11-12 14:06:28

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发布于 2019-11-12 14:06:28

spring.factories

按照以往的惯例，在研究源码的时候，我们先看一下spring.factories文件下自动装配的类FeignAutoConfiguration，其中比较重要的东西有这么几个

@Autowired(required = false)    private List<FeignClientSpecification> configurations = new ArrayList<>();

    @Bean    public FeignContext feignContext() {        FeignContext context = new FeignContext();        context.setConfigurations(this.configurations);        return context;    }
    @Configuration    @ConditionalOnClass(name = "feign.hystrix.HystrixFeign")    protected static class HystrixFeignTargeterConfiguration {        @Bean        @ConditionalOnMissingBean        public Targeter feignTargeter() {            return new HystrixTargeter();        }    }
    @Configuration    @ConditionalOnMissingClass("feign.hystrix.HystrixFeign")    protected static class DefaultFeignTargeterConfiguration {        @Bean        @ConditionalOnMissingBean        public Targeter feignTargeter() {            return new DefaultTargeter();        }    }

属性configurations代表的是各个Feign客户端的配置类，这个稍后会再次提到
FeignContext这个bean看名字就知道，Feign的上下文环境，包含了所有feign客户端的配置
接下来是两个Targeter是看当前是否存在hystrix环境，接下来也会提到
除此之外这个类还包含了HttpClient相关的配置就不展开了

`@EnableFeignClients`注解解析

查看完自动装配的类，接着看@EnableFeignClients注解

进入这个注解发现，它引入了配置类 FeignClientsRegistrar，由于这个类实现了ImportBeanDefinitionRegistrar接口，所以按照我们以往的经历直接看一下registerBeanDefinitions方法吧

   public void registerBeanDefinitions(AnnotationMetadata metadata,            BeanDefinitionRegistry registry) {        registerDefaultConfiguration(metadata, registry);         registerFeignClients(metadata, registry);    }

这里分为了2步

注册缺省配置

private void registerDefaultConfiguration(AnnotationMetadata metadata,BeanDefinitionRegistry registry) {        // 获取注解@EnableFeignClients的注解属性             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();            }            // 各种信息准备就绪，现在执行注册            registerClientConfiguration(registry, name,                    defaultAttrs.get("defaultConfiguration"));        }    }    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());    }

可以看到这里就是处理注册@EnableFeignClients上defaultConfiguration属性所指定的客户端的缺省配置，注意这里配置都是注册为了FeignClientSpecification类型的bean，这个类型的bean也是本文刚开始提到的被Feign上下文持有的各个Feign客户端持有的

注册各个`Feign`客户端

public void registerFeignClients(AnnotationMetadata metadata,                                 BeanDefinitionRegistry registry) {    ClassPathScanningCandidateComponentProvider scanner = getScanner();    scanner.setResourceLoader(this.resourceLoader);
    Set<String> basePackages;
    Map<String, Object> attrs = metadata        .getAnnotationAttributes(EnableFeignClients.class.getName());    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) {                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"));                 registerFeignClient(registry, annotationMetadata, attributes);            }        }    }

这里一共分为3个步骤：

使用ClassPathScanningCandidateComponentProvider扫描所有的标注了@FeignClient注解的接口
将注解上包含的属性作为bean注册，这些属性也就是每个Feign客户端端的配置
将@Feign客户端注册

private void registerFeignClient(BeanDefinitionRegistry registry,                                 AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {    // 1.获取标注@Feign注解的接口名称    String className = annotationMetadata.getClassName();
    // 2.使用BeanDefinitionBuilder构造bean：FeignClientFactoryBean    BeanDefinitionBuilder definition = BeanDefinitionBuilder        .genericBeanDefinition(FeignClientFactoryBean.class);    validate(attributes);
    // 3.添加FeignClientFactoryBean的各个属性    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);
    // 4.设置别名    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;    }
    // 5.注册FeignClientFactoryBean    BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,                                                           new String[] { alias });    BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);}

上方这个方法通过了5步把各个FeignClient都注册成了bean：FeignClientFactoryBean，相信看过之前文章的同学都知道FactoryBean系列的bean是干什么的了。而Feign整合Ribbon和Hystrix的核心应该也在这个类里面了

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原始发表：2019-11-04，如有侵权请联系 cloudcommunity@tencent.com 删除

spring