SpringCloud 2.x学习笔记：3、Hystrix（Greenwich版本）

雨点打透心脏的1/2处 2022-04-25 10:20 292阅读 0赞

### 1、Hystrix基本思想 ###

在分布式系统当中，服务之间调用关系会随着业务的发展而变的复杂，一个服务可能依赖多个服务，服务之间层层依赖；一个服务的瘫痪可能导致整个系统的崩溃。

与电闸思想类似：每栋房子，每户都安装了电闸，电闸的作用是保证有一家电路出现短路时，电闸进行断电跳闸的操作，这样不至于导致整栋楼用电瘫痪。

### 2、新建hystrix模块 ###

#### 2.1 pom文件 ####

<?xml version="1.0" encoding="UTF-8"?>
    <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>
        <groupId>com.cntaiping.tpa</groupId>
        <artifactId>hystrix</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <packaging>jar</packaging>
        <name>hystrix</name>
        <description>Demo project for Spring Boot</description>
    
        <parent>
            <groupId>com.cntaiping.tpa</groupId>
            <artifactId>cloud</artifactId>
            <version>1.0-SNAPSHOT</version>
        </parent>
    
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
            </dependency>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
            </dependency>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
            </dependency>
        </dependencies>
    
    </project>

#### 2.2 配置文件application.properties ####

#服务名称
    spring.application.name=consumer-hystrix
    #端口号
    server.port=8505
    #在注册中心中进行注册
    eureka.client.serviceUrl.defaultZone=http://localhost:8800/eureka/

#### 2.3 Application入口 ####

package com.cntaiping.tpa.hystrix;
    
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.cloud.client.loadbalancer.LoadBalanced;
    import org.springframework.cloud.netflix.hystrix.EnableHystrix;
    import org.springframework.context.annotation.Bean;
    import org.springframework.web.client.RestTemplate;
    
    @SpringBootApplication
    @EnableHystrix
    public class HystrixApplication {
    
        public static void main(String[] args) {
            SpringApplication.run(HystrixApplication.class, args);
        }
    
        @Bean
        @LoadBalanced
        RestTemplate restTemplate() {
            return new RestTemplate();
        }
    }

#### 2.4 服务消费类 ####

在hello方法上加上@HystrixCommand注解。该注解对该方法创建了熔断器的功能，并指定了fallbackMethod熔断方法，熔断方法直接返回了一个字符串

package com.cntaiping.tpa.hystrix.service;
    
    import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Service;
    import org.springframework.web.client.RestTemplate;
    
    @Service
    public class HelloService {
        @Autowired
        RestTemplate restTemplate;
    
        @HystrixCommand(fallbackMethod = "error")
        public String hello(String name) {
            return restTemplate.getForObject("http://producer/get?name="+name, String.class);
        }
    
        public String error(String name) {
            return "hi,"+name+",sorry,error!";
        }
    }

package com.cntaiping.tpa.hystrix.controller;
    
    import com.cntaiping.tpa.hystrix.service.HelloService;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.RequestParam;
    import org.springframework.web.bind.annotation.RestController;
    
    @RestController
    public class HelloController {
        @Autowired
        HelloService helloService;
    
        @GetMapping(value = "/hello")
        public String hello(@RequestParam String name) {
            return helloService.hello( name );
        }
    }

### 3、运行效果 ###

（1）注册中心  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5neXVxaWFuZw_size_16_color_FFFFFF_t_70]  
（2）consumer-hystrix模块  
[http://localhost:8505/hello?name=chengyq][http_localhost_8505_hello_name_chengyq]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5neXVxaWFuZw_size_16_color_FFFFFF_t_70 1]  
（3）测试熔断

将服务提供方producer的两个实例进程（8700和8701）关闭，再次运行http://localhost:8505/hello?name=chengyq

hi,chengyq,sorry,error!

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5neXVxaWFuZw_size_16_color_FFFFFF_t_70 2]  
这就说明当producer模块不可用的时候，consumer-hystrix调用producer的API接口时，会执行快速失败，直接返回一组字符串，而不是等待响应超时，这很好的控制了容器的线程阻塞。

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5neXVxaWFuZw_size_16_color_FFFFFF_t_70]: /images/20220125/d6d0e986a98a4c9b8863d1b25802241e.png
[http_localhost_8505_hello_name_chengyq]: http://localhost:8505/hello?name=chengyq
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5neXVxaWFuZw_size_16_color_FFFFFF_t_70 1]: /images/20220125/2233dca1a4554909a2836b24f2159425.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5neXVxaWFuZw_size_16_color_FFFFFF_t_70 2]: /images/20220125/fb01a0eafb914f7db8c661e9dc530fb3.png