SpringCloud-Hystrix【解决灾难性雪崩-熔断】

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-hystrix</artifactId>
    <version>1.3.2.RELEASE</version>
</dependency>

@EnableCircuitBreaker // 开启熔断 断路器
@EnableEurekaClient
@SpringBootApplication
public class SpringcloudEurekaConsumerApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringcloudEurekaConsumerApplication.class, args);
    }

}

@Service
public class UserService {

    /**
     * ribbon 负载均衡
     *    LoadBalancerClient 通过服务名称可以获取对应的服务的相关信息 ip port等
     */
    @Autowired
   private LoadBalancerClient loadBalancerClient;

    @HystrixCommand(fallbackMethod = "fallback",
            commandProperties = {
                    //默认 20 个;10s 内请求数大于 20 个时就启动熔断器，当请求符合熔断条件时将触发 getFallback()。
            @HystrixProperty(name= HystrixPropertiesManager.CIRCUIT_BREAKER_REQUEST_VOLUME_THRESHOLD,
                    value="10"),
            //请求错误率大于 50%时就熔断，然后 for 循环发起请求，当请求符合熔断条件时将触发 getFallback()。
            @HystrixProperty(name=HystrixPropertiesManager.CIRCUIT_BREAKER_ERROR_THRESHOLD_PERCENTAGE,
                    value="50"),
            //默认 5 秒;熔断多少秒后去尝试请求
            @HystrixProperty(name=HystrixPropertiesManager.CIRCUIT_BREAKER_SLEEP_WINDOW_IN_MILLISECONDS,
                    value="5000"),
            })
    public List<User> getUsers(Integer id){
        System.out.println("--------->"+id);
        if(id == 1){
            throw new RuntimeException();
        }
        // ServiceInstance 封装的有服务的基本信息  IP和端口等
        ServiceInstance si = this.loadBalancerClient.choose("eureka-ribbon-provider");

        StringBuilder sb = new StringBuilder();
        sb.append("http://")
                .append(si.getHost())
                .append(":")
                .append(si.getPort())
                .append("/user");
        System.out.println("服务地址:"+sb.toString());
        // SpringMVC RestTemplate
        RestTemplate rt = new RestTemplate();
        ParameterizedTypeReference<List<User>> type = new ParameterizedTypeReference<List<User>>() {};
        // ResponseEntity:封装了返回值的信息
        ResponseEntity<List<User>> response = rt.exchange(sb.toString(), HttpMethod.GET,null,type);
        List<User> list = response.getBody();
        return list;
    }

    /**
     * 服务降级
     *   返回托底数据的方法
     * @return
     */
    public List<User> fallback(Integer id){
        List<User> list = new ArrayList<>();
        list.add(new User(3,"我是托底数据",22));
        return list;
    }
}