Spring Cloud Hystrix：服务容错与熔断

Spring Cloud Hystrix 是 Netflix 的 Hystrix 的 Spring Cloud 封装，提供了服务的容错和熔断机制。

以下是一个使用 Hystrix 的简单示例：

1. 添加依赖到你的 pom.xml：

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
</dependency>

2. 在你的应用主类或者配置类上添加 @EnableCircuitBreaker 注解启用 Hystrix：

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
 
@SpringBootApplication
@EnableCircuitBreaker
@EnableDiscoveryClient
public class MyApplication {
 
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

3. 使用 HystrixCommand 或 HystrixObservableCommand 创建服务调用的容错逻辑：

import com.netflix.hystrix.HystrixCommand;
import com.netflix.hystrix.HystrixCommandGroupKey;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.client.RestTemplate;
 
public class ServiceCallCommand extends HystrixCommand<String> {
 
    private final RestTemplate restTemplate;
    private final String serviceUrl;
 
    protected ServiceCallCommand(Setter setter, RestTemplate restTemplate, String serviceUrl) {
        super(setter);
        this.restTemplate = restTemplate;
        this.serviceUrl = serviceUrl;
    }
 
    @Override
    protected String run() throws Exception {
        return restTemplate.getForObject(serviceUrl, String.class);
    }
 
    @Override
    protected String getFallback() {
        return "Fallback message";
    }
 
    public static class Factory {
        private final RestTemplate restTemplate;
        private final String serviceUrl;
 
        @Autowired
        public Factory(RestTemplate restTemplate) {
            this.restTemplate = restTemplate;
            this.serviceUrl = "http://your-service-url";
        }
 
        public ServiceCallCommand create() {
            return new ServiceCallCommand(Setter.withGroupKey(
                    HystrixCommandGroupKey.Factory.asKey("ServiceCallGroup")),
                    restTemplate, serviceUrl);
        }
    }
}

4. 在你的服务中调用 HystrixCommand：

public String