扩展Spring Cloud Feign 实现自动降级-白红宇

自动降级目的

在Spring Cloud 使用feign 的时候，需要明确指定fallback 策略，不然会提示错误。

先来看默认的feign service 是要求怎么做的。feign service 定义一个 factory 和 fallback 的类

@FeignClient(value = ServiceNameConstants.UMPS_SERVICE, fallbackFactory = RemoteLogServiceFallbackFactory.class)public interface RemoteLogService {}复制代码

但是我们大多数情况的feign 降级策略为了保证幂等都会很简单，输出错误日志即可。类似如下代码，在企业中开发非常不方便

@Slf4j@Componentpublic class RemoteLogServiceFallbackImpl implements RemoteLogService {	@Setter	private Throwable cause;	@Override	public R
    
      saveLog(SysLog sysLog, String from) {		log.error("feign 插入日志失败", cause);		return null;	}}复制代码

自动降级效果

@FeignClient(value = ServiceNameConstants.UMPS_SERVICE)public interface RemoteLogService {}复制代码

Feign Service 完成同样的降级错误输出

FeignClient 中无需定义无用的fallbackFactory

FallbackFactory 也无需注册到Spring 容器中

代码变化，去掉FeignClient 指定的降级工厂

代码变化，删除降级相关的代码

核心源码

注入我们个性化后的Feign

@Configuration@ConditionalOnClass({HystrixCommand.class, HystrixFeign.class})protected static class HystrixFeignConfiguration {	@Bean	@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)	@ConditionalOnProperty("feign.hystrix.enabled")	public Feign.Builder feignHystrixBuilder(FeignContext feignContext) {		return PigxHystrixFeign.builder(feignContext)				.decode404()				.errorDecoder(new PigxFeignErrorDecoder());	}}复制代码

PigxHystrixFeign.target 方法是根据@FeignClient 注解生成代理类的过程，注意注释

@Overridepublic 
    
      T target(Target
     
       target) {	Class
      
        targetType = target.type();	FeignClient feignClient = AnnotatedElementUtils.getMergedAnnotation(targetType, FeignClient.class);	String factoryName = feignClient.name();	SetterFactory setterFactoryBean = this.getOptional(factoryName, feignContext, SetterFactory.class);	if (setterFactoryBean != null) {		this.setterFactory(setterFactoryBean);	}		// 以下为获取降级策略代码，构建降级，这里去掉了降级非空的非空的校验	Class
        fallback = feignClient.fallback();	if (fallback != void.class) {		return targetWithFallback(factoryName, feignContext, target, this, fallback);	}	Class
        fallbackFactory = feignClient.fallbackFactory();	if (fallbackFactory != void.class) {		return targetWithFallbackFactory(factoryName, feignContext, target, this, fallbackFactory);	}	return build().newInstance(target);}复制代码

构建feign 客户端执行PigxHystrixInvocationHandler的增强

Feign build(@Nullable final FallbackFactory
     nullableFallbackFactory) {		super.invocationHandlerFactory((target, dispatch) ->				new PigxHystrixInvocationHandler(target, dispatch, setterFactory, nullableFallbackFactory));		super.contract(new HystrixDelegatingContract(contract));		return super.build();	}复制代码

PigxHystrixInvocationHandler.getFallback() 获取降级策略

@Override	@Nullable	@SuppressWarnings("unchecked")	protected Object getFallback() {	        // 如果 @FeignClient  没有配置降级策略，使用动态代理创建一个			if (fallbackFactory == null) {				fallback = PigxFeignFallbackFactory.INSTANCE.create(target.type(), getExecutionException());			} else {			  // 如果 @FeignClient配置降级策略，使用配置的				fallback = fallbackFactory.create(getExecutionException());			}	}复制代码

PigxFeignFallbackFactory.create 动态代理逻辑

public T create(final Class
     type, final Throwable cause) {		return (T) FALLBACK_MAP.computeIfAbsent(type, key -> {			Enhancer enhancer = new Enhancer();			enhancer.setSuperclass(key);			enhancer.setCallback(new PigxFeignFallbackMethod(type, cause));			return enhancer.create();		});	}复制代码

PigxFeignFallbackMethod.intercept，默认的降级逻辑，输出降级方法信息和错误信息，并且把错误格式

public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) {	log.error("Fallback class:[{}] method:[{}] message:[{}]",			type.getName(), method.getName(), cause.getMessage());	if (R.class == method.getReturnType()) {		final R result = cause instanceof PigxFeignException ?				((PigxFeignException) cause).getResult() : R.builder()				.code(CommonConstants.FAIL)				.msg(cause.getMessage()).build();		return result;	}	return null;}复制代码

自动降级目的

自动降级效果

代码变化，去掉FeignClient 指定的降级工厂

代码变化，删除降级相关的代码

核心源码

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