SpringCloud Feign 全局Fallback的另一种实现方式（SpringBoot3.4+）

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前言

之前在SpringBoot2.7+中实现 全局Fallback方式较为复杂，且是从Feign入手，现在从断路器入手，通过捕获异常方式实现。

注意：这里基于SpringBoot3.4实现的，如果是2.7那么又会复杂一点，原因是内置的Resilience4JCircuitBreakerFactory实现的接口未返回接口CircuitBreaker而是实现Resilience4JCircuitBreaker，在3.4版本已修正为接口CircuitBreaker。

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一、定制Fegin

请参考之前的实现。

二、定制断路器

因为在未设置断路器时，会抛出NoFallbackAvailableException，所以就通过捕获NoFallbackAvailableException来实现全局Fallback

1.自定义断路器DefaultCircuitBreaker

class DefaultCircuitBreaker implements CircuitBreaker {

    private static final Logger log = LoggerFactory.getLogger(DefaultCircuitBreaker.class);

    private final CircuitBreaker circuitBreaker;

    DefaultCircuitBreaker(CircuitBreaker circuitBreaker) {
        this.circuitBreaker = circuitBreaker;
    }

    @SuppressWarnings("unchecked")
    @Override
    public <T> T run(Supplier<T> toRun, Function<Throwable, T> fallback) {
        try {
            return circuitBreaker.run(toRun, fallback);
        } catch (NoFallbackAvailableException e) {
            Throwable cause = e.getCause();
            String errorMessage = cause.getMessage();
            if (cause instanceof FeignException exception && !exception.contentUTF8().isEmpty()) {
                errorMessage = exception.contentUTF8();
            }
            log.error("Using DefaultFallback handle exception", cause);
            return (T) RestResp.error(ExceptionKeys.REMOTE_SERVICE_ERROR, errorMessage);
        }
    }

}

2.定义Resilience4JCircuitBreakerFactory bean来替换内置断路器

    @Bean
    Resilience4JCircuitBreakerFactory resilience4jCircuitBreakerFactory(CircuitBreakerRegistry circuitBreakerRegistry, TimeLimiterRegistry timeLimiterRegistry,
                                                                        @Autowired(required = false) Resilience4jBulkheadProvider bulkheadProvider,
                                                                        Resilience4JConfigurationProperties resilience4JConfigurationProperties) {
        return new Resilience4JCircuitBreakerFactory(circuitBreakerRegistry,
                timeLimiterRegistry, bulkheadProvider, resilience4JConfigurationProperties) {
            @Override
            public CircuitBreaker create(String id) {
                return new DefaultCircuitBreaker(super.create(id));
            }

            @Override
            public CircuitBreaker create(String id, String groupName) {
                return new DefaultCircuitBreaker(super.create(id, groupName));
            }
        };
    }

封装成Starter

1. 创建一个自动配置类CircuitBreakerAutoConfiguration

@AutoConfiguration(before = Resilience4JAutoConfiguration.class)
@ConditionalOnClass(Resilience4JCircuitBreakerFactory.class)
public class CircuitBreakerAutoConfiguration {

    @Bean
    Resilience4JCircuitBreakerFactory resilience4jCircuitBreakerFactory(CircuitBreakerRegistry circuitBreakerRegistry, TimeLimiterRegistry timeLimiterRegistry,
                                                                        @Autowired(required = false) Resilience4jBulkheadProvider bulkheadProvider,
                                                                        Resilience4JConfigurationProperties resilience4JConfigurationProperties) {
        return new Resilience4JCircuitBreakerFactory(circuitBreakerRegistry,
                timeLimiterRegistry, bulkheadProvider, resilience4JConfigurationProperties) {
            @Override
            public CircuitBreaker create(String id) {
                return new DefaultCircuitBreaker(super.create(id));
            }

            @Override
            public CircuitBreaker create(String id, String groupName) {
                return new DefaultCircuitBreaker(super.create(id, groupName));
            }
        };
    }

}

2. 将配置类添加到配置文件org.springframework.boot.autoconfigure.AutoConfiguration.imports中

3. 如果需要配置一个开关来启用CircuitBreakerAutoConfiguration，也可以添加条件注解ConditionalOnProperty如下

@ConditionalOnProperty(prefix = "mcn.circuitbreaker", name = "default.enabled", havingValue = "true", matchIfMissing = true)