Feign如何构建以及实现自定义扩展功能
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spring-cloud-openfeign-core-2.1.1.RELEASE.jar中 HystrixFeign的详细构建过程:
@EnableFeignClients -> FeignClientsRegistrar 扫描 @Feign注解的类 -> FeignClientFactoryBean通过Targeter生产FeignClient -> Targeter通过Feign.Builder构建Feign -> Feign.Builder
1. 准备工作(配置)
FeignAutoConfiguration自动配置类
@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(); } }
feign.hystrix.HystrixFeign类存在时,将
HystrixTargeter
注册为Targeter
类型的 beanfeign.hystrix.HystrixFeign类不存在时,使用
DefaultTargeter
。看起来似乎可以使用自定义的Targeter代替Hystrix或默认的,这样就可以自定义各种功能了。实际上不行,因为
Targeter
是 package访问级别的。FeignClientsConfiguration
@Configuration public class FeignClientsConfiguration { @Bean @ConditionalOnMissingBean public Retryer feignRetryer() { return Retryer.NEVER_RETRY; } @Bean @Scope("prototype") @ConditionalOnMissingBean public Feign.Builder feignBuilder(Retryer retryer) { return Feign.builder().retryer(retryer); } @Configuration @ConditionalOnClass({ HystrixCommand.class, HystrixFeign.class }) protected static class HystrixFeignConfiguration { @Bean @Scope("prototype") @ConditionalOnMissingBean @ConditionalOnProperty(name = "feign.hystrix.enabled") public Feign.Builder feignHystrixBuilder() { return HystrixFeign.builder(); } } }
重要:Feign 以及内部类 Feign.Builder 都是 public访问级别,可以注入自定义的bean。
2.EnableFeignClients与FeignClientsRegistrar类
将使用@FeignClient注解的类注册成spring bean,并使用注解中的配置
在@EnableFeignClients注解中导入FeignClientsRegistrar类
FeignClientsRegistrar类实现了ImportBeanDefinitionRegistrar类,会由spring框架执行实现方法
registerBeanDefinitions(AnnotationMetaData, BeanDefinitionRegistry)
FeignClientsRegistrar中的
registerBeanDefinitions
方法调用两个方法registerDefaultConfiguration
:注册默认的配置registerFeignClients
:注册Feign客户端(重点)registerFeignClients
:获取@EnableFeignClients
注解中定义的配置扫描feign客户端registerFeignClients
:通过registerFeignClient(BeanDefinitionRegistry, AnnotationMetadata, Map)
方法注册每一个feignClient,过程:先获取@FeignClient
注解中定义的配置,将配置应用在spring bean 工厂FeignClientFactoryBean
, 通过工厂类FeignClientFactoryBean
为每一个使用@FeignClient
注解的类生产FeignClient
,详细过程见下一节
3.FeignClientFactoryBean
FeignClient工厂bean。
class FeignClientFactoryBean implements FactoryBean
通过实现方法 FactoryBean#getObject()
来由spring框架生产FeignClient。
@Override public Object getObject() throws Exception { return getTarget(); } /** * 获得目标 * 1. 获得FeignContext * 2. 从FeignContext中获得Feign构建器Feign.Builder * 3. 从FeignContext中获得Client,判断是否进行负载均衡 * 4. 从FeignContext中获得Target,并执行Target的默认方法target(FeignClientFactoryBean, Feign.Builder, FeignContext, Target.HardCodedTarget); * 5.由于一开始注入的Feign.Builder是HystrixFeign.Builder,则此处是调用HystrixFeign.Builder里的对应方法 */ T getTarget() { FeignContext context = this.applicationContext.getBean(FeignContext.class); Feign.Builder builder = feign(context); //省略部分代码 // ...... Client client = getOptional(context, Client.class); if (client != null) { if (client instanceof LoadBalancerFeignClient) { // not load balancing because we have a url, // but ribbon is on the classpath, so unwrap client = ((LoadBalancerFeignClient) client).getDelegate(); } builder.client(client); } Targeter targeter = get(context, Targeter.class); return (T) targeter.target(this, builder, context, new HardCodedTarget<>(this.type, this.name, url)); } protected Feign.Builder feign(FeignContext context) { FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class); Logger logger = loggerFactory.create(this.type); // @formatter:off Feign.Builder builder = get(context, Feign.Builder.class) // required values .logger(logger) .encoder(get(context, Encoder.class)) .decoder(get(context, Decoder.class)) .contract(get(context, Contract.class)); // @formatter:on configureFeign(context, builder); return builder; }
工厂获得对象(目标):
1. 获得FeignContext(feign上下文) 2. 从FeignContext中获得Feign构建器Feign.Builder(public,可以在此使用自定义构建器) 3. 从FeignContext中获得Client,判断是否进行负载均衡 4. 从FeignContext中获得Target,并执行Target的默认方法target(FeignClientFactoryBean, Feign.Builder, FeignContext, Target.HardCodedTarget); 5. 由于一开始注入的 *Targeter* 是 *HystrixTargeter* ,则此处是调用 HystrixTargeter 里的对应方法(从第一节的配置来看,只要 *feign.hystrix.HystrixFeign* 类存在,就是注入的 *HystrixTargeter *, 否则是 *DefaultTargeter*,对于需要**自定义构建feign的,这里不太重要**)
4.Targeter
4.1.HystrixTargeter
class HystrixTargeter implements Targeter { @Override publicT target(FeignClientFactoryBean factory, Feign.Builder feign, FeignContext context, Target.HardCodedTarget target) { // 若不是 HystrixFeign,则执行其对应的默认target方法。 // 此处只处理HystrixFeign。 if (!(feign instanceof feign.hystrix.HystrixFeign.Builder)) { return feign.target(target); } feign.hystrix.HystrixFeign.Builder builder = (feign.hystrix.HystrixFeign.Builder) feign; SetterFactory setterFactory = getOptional(factory.getName(), context, SetterFactory.class); if (setterFactory != null) { builder.setterFactory(setterFactory); } Class> fallback = factory.getFallback(); if (fallback != void.class) { return targetWithFallback(factory.getName(), context, target, builder, fallback); } Class> fallbackFactory = factory.getFallbackFactory(); if (fallbackFactory != void.class) { return targetWithFallbackFactory(factory.getName(), context, target, builder, fallbackFactory); } // 调用从Feign.Builder继承的方法。 return feign.target(target); } private T targetWithFallbackFactory(String feignClientName, FeignContext context, Target.HardCodedTarget target, HystrixFeign.Builder builder, Class> fallbackFactoryClass) { FallbackFactory extends T> fallbackFactory = (FallbackFactory extends T>) getFromContext( "fallbackFactory", feignClientName, context, fallbackFactoryClass, FallbackFactory.class); return builder.target(target, fallbackFactory); } private T targetWithFallback(String feignClientName, FeignContext context, Target.HardCodedTarget target, HystrixFeign.Builder builder, Class> fallback) { T fallbackInstance = getFromContext("fallback", feignClientName, context, fallback, target.type()); return builder.target(target, fallbackInstance); } //... }
HystrixTarget只处理 Feign.Builder 类型为 feign.hystrix.HystrixFeign.Builder 的
若feign构建器不是 feign.hystrix.HystrixFeign.Builder 类型,则执行注入的 feign 构建器的默认target方法
因此,即使注入的 Targeter 是 HystrixTargeter,此处也可以执行自定义 Feign.Builder。
理解:Feign.Builder#target(Target) 方法通常不会被 override(后续会讲解为什么不重写此方法)
4.2.DefaultTargeter
class DefaultTargeter implements Targeter { @Override publicT target(FeignClientFactoryBean factory, Feign.Builder feign, FeignContext context, Target.HardCodedTarget target) { return feign.target(target); } }
执行 Feign.Builder (子)类型对应的 默认 target方法。
理解:Feign.Builder#target(Target) 方法通常不会被 override(后续会讲解为什么不重写此方法)
5.FeignBuilder
feign构建器:构建feign对象。
Feign的目的是将 http api 包装成 restful 风格以便开发。
在实现中,Feign 是一个为目标http apis 生成 feign对象(
Feign#newInstance
)的工厂。
上述步骤目前需要的都是通过对应的 Builder 构建对应的Feign。
public abstract class Feign { public static Builder builder() { return new Builder(); } public abstractT newInstance(Target target); public static class Builder { public T target(Target target) { return build().newInstance(target); } public Feign build() { SynchronousMethodHandler.Factory synchronousMethodHandlerFactory = new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger, logLevel, decode404, closeAfterDecode, propagationPolicy); ParseHandlersByName handlersByName = new ParseHandlersByName(contract, options, encoder, decoder, queryMapEncoder, errorDecoder, synchronousMethodHandlerFactory); return new ReflectiveFeign(handlersByName, invocationHandlerFactory, queryMapEncoder); } } }
Feign.Builder#target(Target) 方法里面实际上调用的是 build()方法来构建对象,因此重写 build() 方法即可,没有必要还重写 target(Target) 方法
Feign以及内部类 Feign.Builder都是 public ,可以重写并注入自定义的bean。
5.1.HystrixFeign
public final class HystrixFeign { public static final class Builder extends Feign.Builder { @Override public Feign build() { return build(null); } // 提供一系列的target方法,支持各种配置:fallback、FallBackFactory等 publicT target(Target target, T fallback) { return build(fallback != null ? new FallbackFactory.Default (fallback) : null) .newInstance(target); } public T target(Target target, FallbackFactory extends T> fallbackFactory) { return build(fallbackFactory).newInstance(target); } public T target(Class apiType, String url, T fallback) { return target(new Target.HardCodedTarget (apiType, url), fallback); } public T target(Class apiType, String url, FallbackFactory extends T> fallbackFactory) { return target(new Target.HardCodedTarget (apiType, url), fallbackFactory); } /** Configures components needed for hystrix integration. */ Feign build(final FallbackFactory> nullableFallbackFactory) { super.invocationHandlerFactory(new InvocationHandlerFactory() { @Override public InvocationHandler create(Target target, Map dispatch) { return new HystrixInvocationHandler(target, dispatch, setterFactory, nullableFallbackFactory); } }); super.contract(new HystrixDelegatingContract(contract)); return super.build(); }
基本到了这一步,需要设置的东西,都可以配置了。
虽然 build 方法中涉及到 InvocationHandler,但基本不需要改什么,而 InvocationHandler 竟然也是 package 访问级别,所以只好复制一个,使用自己的。
HystrixDelegatingContract 是 public 级别,不需要修改的话,仍然用这个。
5.2示例
以下示例参考 SentinelFeign
其中的 YiFeiXiInvocationHandler
和 YiFeiXiFeignFallbackFactory
是自定义的。
@Override public Feign build() { super.invocationHandlerFactory(new InvocationHandlerFactory() { @Override public InvocationHandler create(Target target, Mapdispatch) { // using reflect get fallback and fallbackFactory properties from // FeignClientFactoryBean because FeignClientFactoryBean is a package // level class, we can not use it in our package Object feignClientFactoryBean = Builder.this.applicationContext .getBean("&" + target.type().getName()); Class fallback = (Class) getFieldValue(feignClientFactoryBean, "fallback"); Class fallbackFactory = (Class) getFieldValue(feignClientFactoryBean, "fallbackFactory"); String name = (String) getFieldValue(feignClientFactoryBean, "name"); Object fallbackInstance; FallbackFactory fallbackFactoryInstance; // check fallback and fallbackFactory properties // 以下逻辑在HystrixTargeter中有,但执行自定义的builder,不会执行到那段逻辑,因此此处加上。 if (void.class != fallback) { fallbackInstance = getFromContext(name, "fallback", fallback, target.type()); return new YiFeiXiInvocationHandler(target, dispatch, setterFactory, new FallbackFactory.Default(fallbackInstance)); } if (void.class != fallbackFactory) { fallbackFactoryInstance = (FallbackFactory) getFromContext(name, "fallbackFactory", fallbackFactory, FallbackFactory.class); return new YiFeiXiInvocationHandler(target, dispatch, setterFactory, fallbackFactoryInstance); } // 若注解中没有使用fallback或fallbackFactory,则使用一个默认的FallbackFactory。 return new YiFeiXiInvocationHandler(target, dispatch, setterFactory, new YiFeiXiFeignFallbackFactory<>(target)); } private Object getFromContext(String name, String type, Class fallbackType, Class targetType) { Object fallbackInstance = feignContext.getInstance(name, fallbackType); if (fallbackInstance == null) { throw new IllegalStateException(String.format( "No %s instance of type %s found for feign client %s", type, fallbackType, name)); } if (!targetType.isAssignableFrom(fallbackType)) { throw new IllegalStateException(String.format( "Incompatible %s instance. Fallback/fallbackFactory of type %s is not assignable to %s for feign client %s", type, fallbackType, targetType, name)); } return fallbackInstance; } }); super.contract(new HystrixDelegatingContract(contract)); return super.build(); }
需要自定义fallbackFactory,则实现 feign.hystrix.FallbackFactory类,需要自定义fallback,则实现 org.springframework.cglib.proxy.MethodInterceptor即可
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