Spring Cloud 学习(12) --- Hystrix(一) Hystrix 介绍、Feign Hystrix 断路器

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wx611f65369a431 2021-08-22 11:02:59

文章标签 spring java ide .net jar 文章分类 Java 后端开发

Hystrix 是一个延迟和容错库，目的在隔离远程系统、服务、第三方库，组织级联故障，在负载的分布式系统中实现恢复能力。
在多系统和微服务的情况下，需要一种机制来处理延迟和故障，并保护整合系统处于可用的稳定状态。Hystrix 就是实现这个功能的一个组件。

通过客户端库对延迟和故障进行保护和控制。
在一个复杂的分布式系统中停止级联故障
快速失败、迅速恢复
在合理的情况下回退、优雅降级
开启近实时监控、告警、操作控制

实例

源码：https://gitee.com/laiyy0728/spring-cloud/tree/master/spring-cloud-hystrix/spring-cloud-hystrix-simple

pom 依赖

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

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
    </dependencies>

配置文件

spring:
  application:
    name: spring-cloud-hystrix-simple
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/
  instance:
    instance-id: ${spring.application.name}:${server.port}
    prefer-ip-address: true
server:
  port: 8888

Service、ServiceImpl、Controller、启动类

// Service
public interface HystrixService {

    String getUser(String username) throws Exception;

}


// Service Impl
@Service
public class HystrixServiceImpl implements HystrixService {
    @Override
    @HystrixCommand(fallbackMethod = "defaultUser")
    public String getUser(String username) throws Exception {
        if ("laiyy".equals(username)) {
            return "this is real user, name:" + username;
        }
        throw new Exception();
    }

    /**
     * 在 getUser 出错时调用
     */
    public String defaultUser(String username) {
        return "this is error user, name: " + username;
    }

}


// Controller
@RestController
public class HystrixController {

    private final HystrixService hystrixService;

    @Autowired
    public HystrixController(HystrixService hystrixService) {
        this.hystrixService = hystrixService;
    }

    @GetMapping(value = "get-user")
    public String getUser(@RequestParam String username) throws Exception{
        return hystrixService.getUser(username);
    }
}


// Controller
@SpringBootApplication
@EnableDiscoveryClient
@EnableHystrix
public class SpringCloudHystrixSimpleApplication {

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

}

验证

访问 http://localhost:8888/get-user

传入正确 username

Spring Cloud 学习(12) --- Hystrix(一) Hystrix 介绍、Feign Hystrix 断路器_spring

正确 username

传入错误 username

Spring Cloud 学习(12) --- Hystrix(一) Hystrix 介绍、Feign Hystrix 断路器_java_02

错误 username

注解、解释

在上例中，可以发现，在启动类上多了 @EnableHystrix 注解，在 Service 中多了 @HystrixCommand(fallbackMethod = "defaultUser") 和一个名称为 defaultUser 的方法。

@EnableHystrix：开启 Hystrix 断路器
@HystrixCommand：fallbackMethod 指定当该注解标记的方法出现失败、错误时，调用哪一个方法进行优雅的降级返回，对用户屏蔽错误，做优雅提示。

@HystrixCommand 需要注意

fallbackMethod 的值，为方法名。如果方法指定的方法名不存在，会出现如下错误：

com.netflix.hystrix.contrib.javanica.exception.FallbackDefinitionException: fallback method wasn't found: defaultUser1([class java.lang.String])
    at com.netflix.hystrix.contrib.javanica.utils.MethodProvider$FallbackMethodFinder.doFind(MethodProvider.java:190) ~[hystrix-javanica-1.5.12.jar:1.5.12]
    at com.netflix.hystrix.contrib.javanica.utils.MethodProvider$FallbackMethodFinder.find(MethodProvider.java:159) ~[hystrix-javanica-1.5.12.jar:1.5.12]
    at com.netflix.hystrix.contrib.javanica.utils.MethodProvider.getFallbackMethod(MethodProvider.java:73) ~[hystrix-javanica-1.5.12.jar:1.5.12]
    at com.netflix.hystrix.contrib.javanica.utils.MethodProvider.getFallbackMethod(MethodProvider.java:59) ~[hystrix-javanica-1.5.12.jar:1.5.12]
    ...

fallbackMethod 方法的参数与 @HystrixCommand 标注的参数类型、顺序一致，如果不一致，会出现如下错误：

com.netflix.hystrix.contrib.javanica.exception.FallbackDefinitionException: fallback method wasn't found: defaultUser([class java.lang.String])
    at com.netflix.hystrix.contrib.javanica.utils.MethodProvider$FallbackMethodFinder.doFind(MethodProvider.java:190) ~[hystrix-javanica-1.5.12.jar:1.5.12]
    at com.netflix.hystrix.contrib.javanica.utils.MethodProvider$FallbackMethodFinder.find(MethodProvider.java:159) ~[hystrix-javanica-1.5.12.jar:1.5.12]
    ...

断路器

源码：https://gitee.com/laiyy0728/spring-cloud/tree/master/spring-cloud-hystrix/spring-cloud-hystrix-feign-broker

断路器的作用：在服务出现错误的时候，熔断该服务，保护调用者，防止出现雪崩。

在使用 feign 断路器时，feign 默认是不开启 Hystrix 断路器的，需要手动配置。

pom

<dependencies>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-openfeign</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
    </dependency>
</dependencies>

配置文件

application.yml

feign:
  hystrix:
    enabled: true

boorstrap.yml

spring:
  application:
    name: spring-cloud-hystrix-feign-broker
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/
  instance:
    instance-id: ${spring.application.name}:${server.port}
    prefer-ip-address: true
server:
  port: 8888

feign、Fallback、Controller、启动类

// feign
@FeignClient(name = "spring-cloud-ribbon-provider",fallback = FeignHystrixClientFallback.class)
public interface FeignHystrixClient {

    @RequestMapping(value = "/check", method = RequestMethod.GET)
    String feignHystrix();

}


// fallback
@Component
public class FeignHystrixClientFallback implements FeignHystrixClient {
    @Override
    public String feignHystrix() {
        return "error! this is feign hystrix";
    }
}

// controller
@RestController
public class FeignHystrixController {

    private final FeignHystrixClient feignHystrixClient;

    @Autowired
    public FeignHystrixController(FeignHystrixClient feignHystrixClient) {
        this.feignHystrixClient = feignHystrixClient;
    }

    @GetMapping(value = "feign-hystrix")
    public String feignHystrix(){
        return feignHystrixClient.feignHystrix();
    }
}


// 启动类
@SpringBootApplication
@EnableHystrix
@EnableDiscoveryClient
@EnableFeignClients
public class SpringCloudHystrixFeignBrokerApplication {

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

}