SpringCloud学习笔记(4):Hystrix容错机制

简介

在微服务架构中,微服务之间的依赖关系错综复杂,难免的某些服务会出现故障,导致服务调用方出现远程调度的线程阻塞。在高负载的场景下,如果不做任何处理,可能会引起级联故障,导致服务调用方的资源耗尽甚至整个系统奔溃。Hystrix是一个由Netflix开源的一个延迟和容错库,它通过添加延迟容忍和容错逻辑来帮助控制这些微服务之间的交互。Hystrix通过隔离服务之间的访问点、停止跨服务的级联故障并提供回退选项来实现这一点,所有这些选项都提高了系统的总体弹性。

项目介绍

  1. sc-parent,父模块(请参照 SpringCloud学习笔记(1):Eureka注册中心 )
  2. sc-eureka,注册中心(请参照 SpringCloud学习笔记(1):Eureka注册中心 )
  3. sc-provider,提供者(请参照 SpringCloud学习笔记(1):Eureka注册中心 )
  4. sc-consumer-hystrix-ribbon,使用Hystrix+Ribbon的消费者
  5. sc-consumer-hystrix-feign,使用Hystrix+Feign的消费者

在Ribbon上使用Hystrix

1.在父模块下创建子模块项目sc-consumer-hystrix-ribbon,pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>com.cf</groupId>
    <artifactId>sc-parent</artifactId>
    <version>0.0.1-SNAPSHOT</version>
  </parent>
  <artifactId>sc-consumer-hystrix-ribbon</artifactId>
  
  <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-netflix-hystrix</artifactId>
    </dependency>
  </dependencies>
</project>

2.创建启动类consumer.ConsumerApplication:

package consumer;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableCircuitBreaker
public class ConsumerApplication {

    public static void main(String[] args) {
        SpringApplication.run(ConsumerApplication.class, args);
    }
    
    //为RestTemplate整合Ribbon,使其具备负载均衡的能力
    @LoadBalanced
    @Bean
    public RestTemplate restTemplate(){
        return new RestTemplate();
    }
}

3.创建调用提供者服务的Controller:consumer.controller.ConsumerController

package consumer.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;

@RestController
public class ConsumerController {
    @Autowired
    private RestTemplate restTemplate;
    
    @HystrixCommand(fallbackMethod="getBookListFallBack")
    @GetMapping("/getBookList")
    public String getBookList(){
        return restTemplate.getForObject("http://sc-provider/book/list", String.class);
    }
    
    public String getBookListFallBack(){
        return "[\"Java入门到放弃\"]";
    }
}

@HystrixCommand:表示将getBookList方法作为hystrix命令调用的方法。

fallbackMethod:指定处理回退逻辑的方法,这里是getBookListFallBack方法,当getBookList方法跑出异常时将会调用getBookListFallBack方法。

注意:回退方法应该与作为hystrix命令调用的方法具有相同的签名。

4.创建application.yml:

server:
  port: 8083

spring:
  application:
    name: sc-consumer-hystrix-ribbon
    
eureka:
  client:
    registerWithEureka: false
    serviceUrl:
      defaultZone: http://localhost:8080/eureka/

5.测试

依次启动注册中心sc-eureka、提供者sc-provider、消费者sc-consumer-hystrix-ribbon,并访问http://localhost:8083/getBookList,结果显示如下:

这是提供者正常返回的值,接下来将提供者sc-provider关闭,再次访问http://localhost:8083/getBookList,结果显示如下:

因为将提供者sc-provider关闭后,消费者再访问提供者时会报错,Hystrix捕获异常后会直接调用回退方法也就是getBookListFallBack方法。

在Feign上使用Hystrix

1.在父模块下创建子模块项目sc-consumer-hystrix-feign,pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>com.cf</groupId>
    <artifactId>sc-parent</artifactId>
    <version>0.0.1-SNAPSHOT</version>
  </parent>
  <artifactId>sc-consumer-hystrix-feign</artifactId>
  
  <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>
</project>

2.创建启动类feign.FeignApplication:

package feign;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableFeignClients
@EnableCircuitBreaker
public class FeignApplication {
    public static void main(String[] args) {
        SpringApplication.run(FeignApplication.class, args);
    }
}

3.创建Feign声明式接口:feign.inter.BookService

package feign.inter;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.PostMapping;

import feign.fallback.BookFallBack;

@FeignClient(value="sc-provider", fallbackFactory=BookFallBack.class)
public interface BookService {
    
    @GetMapping("/book/list")
    public String getBookList();
}

@FeignClient注解中的fallbackFactory属性是指定的Feign客户端界面定义回退工厂。

4.创建调用提供者服务的Controller:

package feign.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import feign.inter.BookService;

@RequestMapping("/feign")
@RestController
public class FeignController {
    @Autowired
    private BookService bookService;
    
    @GetMapping("/getBookList")
    public String getBookList(){
        return bookService.getBookList();
    }
}

5.创建application.yml:

server:
  port: 8084

spring:
  application:
    name: sc-consumer-hystrix-feign

eureka:
  client:
    registerWithEureka: false
    serviceUrl:
      defaultZone: http://localhost:8080/eureka/   

feign:
  hystrix:
    enabled: true  #开启hystrix支持

6.创建回退工厂类:

package feign.fallback;
import org.springframework.stereotype.Component;

import feign.hystrix.FallbackFactory;
import feign.inter.BookService;

@Component
public class BookFallBack implements FallbackFactory<BookService>{
    @Override
    public BookService create(Throwable cause) {
        return new BookService() {
            @Override
            public String getBookList() {
                return "[\"Java入门到放弃\"]";
            }
        };
    }
}

create方法返回一个回退实例,回退实例为Feign声明式接口BookService的实现类,提供了与BookService相对应的回退方法,BookService接口调用失败时将会调用该实现类中的回退方法。

7.测试:

依次启动注册中心sc-eureka、提供者sc-provider、消费者sc-consumer-hystrix-feign,并访问http://localhost:8084/feign/getBookList,结果显示如下:

这是提供者正常返回的值,接下来将提供者sc-provider关闭,再次访问http://localhost:8084/feign/getBookList,结果显示如下:

8.查看回退原因

修改回退工厂类BookFallBack:

@Component
public class BookFallBack implements FallbackFactory<BookService>{
    @Override
    public BookService create(Throwable cause) {
        return new BookService() {
            @Override
            public String getBookList() {
                //将回退原因输出到控制台
                cause.printStackTrace(System.out);
                return "[\"Java入门到放弃\"]";
            }
        };
    }
}

依次启动注册中心sc-eureka、消费者sc-consumer-hystrix-feign,并访问http://localhost:8084/feign/getBookList,控制台输出:

com.netflix.hystrix.exception.HystrixTimeoutException
    at com.netflix.hystrix.AbstractCommand$HystrixObservableTimeoutOperator$1.run(AbstractCommand.java:1142)
    at com.netflix.hystrix.strategy.concurrency.HystrixContextRunnable$1.call(HystrixContextRunnable.java:41)
    at com.netflix.hystrix.strategy.concurrency.HystrixContextRunnable$1.call(HystrixContextRunnable.java:37)
    at com.netflix.hystrix.strategy.concurrency.HystrixContextRunnable.run(HystrixContextRunnable.java:57)
    at com.netflix.hystrix.AbstractCommand$HystrixObservableTimeoutOperator$2.tick(AbstractCommand.java:1159)
        ......
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