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)

 

publicinterfaceRemoteLogService{}

 

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

 

@Component

 

publicclassRemoteLogServiceFallbackImplimplementsRemoteLogService{

 

@Setter

 

privateThrowable cause;

 

@Override

 

public R<Boolean> saveLog(SysLog sysLog,Stringfrom){

 

log.error("feign 插入日志失败", cause);

 

returnnull;

 

}

 

}

 

自动降级效果

 

@FeignClient(value =ServiceNameConstants.UMPS_SERVICE)

 

publicinterfaceRemoteLogService{}

 

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

 

1. 注入我们个性化后的Feign

 

@Configuration

 

@ConditionalOnClass({HystrixCommand.class,HystrixFeign.class})

 

protectedstaticclassHystrixFeignConfiguration{

 

@Bean

 

@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)

 

@ConditionalOnProperty("feign.hystrix.enabled")

 

publicFeign.Builder feignHystrixBuilder(FeignContext feignContext){

 

returnPigxHystrixFeign.builder(feignContext)

 

.decode404()

 

.errorDecoder(newPigxFeignErrorDecoder());

 

}

 

}

 

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

 

@Override

 

public<T> T target(Target<T> target){

 

Class<T> 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);

 

}

 

3. 构建feign 客户端执行PigxHystrixInvocationHandler的增强

 

Feign build(@NullablefinalFallbackFactory<?> nullableFallbackFactory){

 

super.invocationHandlerFactory((target, dispatch)->

 

newPigxHystrixInvocationHandler(target, dispatch, setterFactory, nullableFallbackFactory));

 

super.contract(newHystrixDelegatingContract(contract));

 

returnsuper.build();

 

}

 

4. PigxHystrixInvocationHandler.getFallback() 获取降级策略

 

@Override

 

@Nullable

 

@SuppressWarnings("unchecked")

 

protectedObject 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());

 

}

 

}

 

5. PigxFeignFallbackFactory.create 动态代理逻辑

 

public T create(finalClass<?> type,finalThrowable cause){

 

return(T) FALLBACK_MAP.computeIfAbsent(type, key ->{

 

Enhancer enhancer =newEnhancer();

 

enhancer.setSuperclass(key);

 

enhancer.setCallback(newPigxFeignFallbackMethod(type, cause));

 

return enhancer.create();

 

});

 

}

 

6. 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

 

publicObject 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 instanceofPigxFeignException?

 

((PigxFeignException) cause).getResult(): R.builder()

 

.code(CommonConstants.FAIL)

 

.msg(cause.getMessage()).build();

 

return result;

 

}

 

returnnull;

 

}