自動降級目的
在Spring Cloud 使用feign 的時候，需要明確指定fallback 策略，不然會提示錯誤。
先來看預設的feign service 是要求怎麼做的。feign service 定義一個 factory 和 fallback 的類
@FeignClient(value = ServiceNameConstants.UMPS_SERVICE, fallbackFactory = RemoteLogServiceFallbackFactory.class)
public interface RemoteLogService {}但是我們大多數情況的feign 降級策略為了保證冪等都會很簡單，輸出錯誤日誌即可。
類似如下程式碼，在企業中開發非常不方便
@Slf4j
@Component
public class RemoteLogServiceFallbackImpl implements RemoteLogService {
@Setter
private Throwable cause;
@Override
public R<Boolean> saveLog(SysLog sysLog, String from) {
log.error("feign 插入日誌失敗", cause);
return null;
}
}自動降級效果
@FeignClient(value = ServiceNameConstants.UMPS_SERVICE)
public interface RemoteLogService {}- Feign Service 完成同樣的降級錯誤輸出
- FeignClient 中無需定義無用的fallbackFactory
- FallbackFactory 也無需註冊到Spring 容器中
程式碼變化，去掉FeignClient 指定的降級工廠
程式碼變化，刪除降級相關的程式碼
核心原始碼
- 注入我們個性化後的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());
}
}- PigxHystrixFeign.target 方法是根據@FeignClient 註解生成代理類的過程，注意註釋
@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);
}
// 以下為獲取降級策略程式碼，構建降級，這裡去掉了降級非空的非空的校驗
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);
}- 構建feign 客戶端執行PigxHystrixInvocationHandler的增強
Feign build(@Nullable final FallbackFactory<?> nullableFallbackFactory) {
super.invocationHandlerFactory((target, dispatch) ->
new PigxHystrixInvocationHandler(target, dispatch, setterFactory, nullableFallbackFactory));
super.contract(new HystrixDelegatingContract(contract));
return super.build();
}- PigxHystrixInvocationHandler.getFallback() 獲取降級策略
@Override
@Nullable
@SuppressWarnings("unchecked")
protected Object getFallback() {
// 如果 @FeignClient 沒有配置降級策略，使用動態代理建立一個
if (fallbackFactory == null) {
fallback = PigxFeignFallbackFactory.INSTANCE.create(target.type(), getExecutionException());
} else {
// 如果 @FeignClient配置降級策略，使用配置的
fallback = fallbackFactory.create(getExecutionException());
}
}- PigxFeignFallbackFactory.create 動態代理邏輯
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();
});
}- PigxFeignFallbackMethod.intercept， 預設的降級邏輯，輸出降級方法資訊和錯誤資訊，並且把錯誤格式
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;
}