Spring Cloud Hystrix：服务容错保护

Spring Cloud Hystrix 是 Netflix 的 Hystrix 的一个 Spring 集成，用于提供分布式系统的服务容错保护。以下是一个使用 Hystrix 的简单示例：

1. 添加 Maven 依赖：

<dependencies>
    <!-- Spring Cloud Hystrix 依赖 -->
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
    </dependency>
</dependencies>
 
<dependencyManagement>
    <dependencies>
        <!-- Spring Cloud 版本管理 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>Finchley.SR2</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

2. 在 Spring Boot 应用的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 包装可能失败的服务调用：

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(RestTemplate restTemplate, String serviceUrl) {
        super(HystrixCommandGroupKey.Factory.asKey("ServiceCallGroup"));
        this.restTemplate = restTemplate;
        this.serviceUrl = serviceUrl;
    }
 
    @Override
    protected String run() {
        return restTemplate.getForObject(serviceUrl, String.class);
    }
 
    @Override
    protected String getFallback() {
        return "Fallback message - service is unavailable";
    }
}

4. 在服务中调用 HystrixCommand：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
 
@Service
public class MyS