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：

org.springframework.boot

spring-boot-starter-web

1.5.10.RELEASE

org.springframework.cloud

spring-cloud-starter-netflix-eureka-client

1.4.3.RELEASE

org.springframework.cloud

spring-cloud-starter-netflix-hystrix

1.4.3.RELEASE

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