springcloud熔断机制

熔断机制，指的是微服务架构中，由于某个服务瘫痪，为避免影响整个系统而采取的降级服务

简述：

由于网络或自身原因，服务不能确保一定可用。如果某个服务出现了问题，调用方的大量请求会使Servlet容器的线程资源被耗尽，导致服务瘫痪。而且这种故障会传播，进而威胁到这个微服务系统可用性

示例如下：基于springboot1.5.10

添加依赖：

 <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>1.5.10.RELEASE</version>
        </dependency>
        <!--Eureka 客户端-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
            <version>1.4.3.RELEASE</version>
        </dependency>
        <!--hystrix断路器-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
            <version>1.4.3.RELEASE</version>
        </dependency>

application配置

server:
  port: 8901 #程序启动端口，也是Tomcat端口
spring:
  application:
    name: customer-order-hystrix #应用别名
eureka:
  client:
    service-url:
      defaultZone: http://user:123@localhost:10000/eureka
  instance:
    instance-id: ${spring.cloud.client.ipAddress}:${spring.application.name}:${spring.application.instance_id:${server.port}}
    prefer-ip-address: true

　　启动类

@SpringBootApplication
@EnableEurekaClient
@EnableCircuitBreaker //启用熔断
public class CustomerHystrixApplication
{
    @Bean
    public RestTemplate getTemp(){
        return new RestTemplate();
    }
    public static void main( String[] args )
    {
        SpringApplication.run(CustomerHystrixApplication.class,args);
        System.out.println("customer start-up success");
    }
}

实体类

public class User {
    private Long id;
    private Date date;

    public User() {

    }

    public User(Long id) {
        this.id = id;
        this.date = new Date();
    }

    public void setId(Long id) {
        this.id = id;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public Long getId() {
        return id;
    }

    public Date getDate() {
        return date;
    }

Controller

@RestController
public class CustomeController {
    @Autowired
    private EurekaClient eurekaClient;

    @Autowired
    private RestTemplate restTemplate;//springboot提供的用于访问rest接口的对象

    @GetMapping("/order/{id}")
    @HystrixCommand(fallbackMethod = "errora1")
    public User getOrder(@PathVariable Long id){
        InstanceInfo instanceInfo = eurekaClient.getNextServerFromEureka("provider-user", false);
        String homePageUrl = instanceInfo.getHomePageUrl();
        // 访问提供者，获取数据
        User user = restTemplate.getForObject(homePageUrl+"/user/" + id,User.class);//通过访问rest获取json数据，然后转换成user对象
        return user;
    }

    /**
     * 失败后执行的回调函数
     * @param id
     * @return
     */
    public User errora1(Long id) {
        User user = new User();
        user.setId(-1000L);
        user.setDate(new Date());
        return user;
    }
}

　　注：回调函数和其使用者应返回相同的类型，这里省略了服务提供者模块 provider-user