“Hello everyone! ”
断路器（Hystrix）简介
断路器（Hystrix）由来：
在微服务架构中，根据业务来拆分成一个个的服务，服务与服务之间可以相互调用（RPC），在Spring Cloud可以用RestTemplate+Ribbon和Feign来调用。 为了保证其高可用，单个服务通常会集群部署。由于网络原因或者自身的原因，服务并不能保证100%可用，如果单个服务出现问题，调用这个服务就会出 现线程阻塞，此时若有大量的请求涌入，Servlet容器的线程资源会被消耗完毕，导致服务瘫痪。服务与服务之间的依赖性，故障会传播，会对整个微服务 系统造成灾难性的严重后果，这就是服务故障的“雪崩”效应。为了解决这个问题，业界提出了断路器模型。
Netflix创建了一个名为hystrix的库，用于实现断路器模式。在微服务体系结构中，通常有多个服务调用层。
第一步：创建条件
这一篇文章基于上一篇文章的工程， 启动EurekaServer工程；启动EurekaClient工程，它的端口为8762
第二步：在ribbon使用断路器：
右键工程->创建module->选择spring initialir->web->web,cloud discovery->eureka discovery,cloud routing->ribbon,cloud circuit breaker->hystrix,然后一直下一步就行了。
创建完成后：
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<?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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.1.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.test</groupId>
<artifactId>service-ribbon</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>service-ribbon</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
<spring-cloud.version>Greenwich.RC2</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<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>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
</repository>
</repositories>
</project>
配置appication.yml文件：
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server:
port: 9873
eureka:
client:
service-url:
defaultZone: http://localhost:9871/eureka/
spring:
application:
name: service-ribbon
第三步 配置启动类
在工程的启动类中添加@EnableHystrix注解开启Hystrix：
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import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;
@SpringBootApplication
@EnableEurekaClient
@EnableDiscoveryClient
@EnableHystrix
public class ServiceRibbonApplication {
public static void main(String[] args) {
SpringApplication.run(ServiceRibbonApplication.class, args);
}
@Bean
@LoadBalanced
RestTemplate restTemplate(){
return new RestTemplate();
}
}
第四步：改写HelloService类
在helloService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，代码如下：
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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 = "helloError")
public String helloService(String name){
return restTemplate.getForObject("http://eureka-client/hello?name=" + name,String.class);
}
public String helloError(String name){
return "hello,"+name+",sorry,error!";
}
}
第五步：改写主程序类
ServiceRibbonApplication加@EnableHystrix注解开启Hystrix，代码如下：
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import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;
@SpringBootApplication
@EnableEurekaClient
@EnableDiscoveryClient
@EnableHystrix
public class ServiceRibbonApplication {
public static void main(String[] args) {
SpringApplication.run(ServiceRibbonApplication.class, args);
}
@Bean
@LoadBalanced
RestTemplate restTemplate(){
return new RestTemplate();
}
}
第六步：启动所有工程
打开 http://localhost:9873/hello?name=handsomeman ，你会在浏览器上看到显示：
hello: handsomeman,i am from port:9872
当我们关闭eureka-client工程时，再次访问 http://localhost:9873/hello?name=handsomeman，浏览器会显示：
hello,handsomeman,sorry,error!
这就说明当eureka-client工程不可用的时候，service-ribbon调用eureka-client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。
第七步：Feign中使用断路器
右键工程->创建module->选择spring initialir->web->web,cloud discovery->eureka discovery,cloud routing->feign,然后一直下一步就行了。
创建完成后：
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<?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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.1.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.test</groupId>
<artifactId>service-feign</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>service-feign</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
<spring-cloud.version>Greenwich.RC2</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<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.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
</repository>
</repositories>
</project>
配置appication.yml文件
Feign是自带断路器的，它没有默认打开。需要在配置文件中配置打开它，在配置文件加以下代码：
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server:
port: 9874
eureka:
client:
service-url:
defaultZone: http://localhost:9871/eureka/
spring:
application:
name: service-feign
feign:
hystrix:
enabled: true
第八步 改写HelloService类
只需要在HelloService接口的注解中加上fallback的指定类：
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import com.test.servicefeign.service.impl.HelloServiceImpl;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
@FeignClient(value = "eureka-client",fallback = HelloServiceImpl.class)
public interface HelloService {
@RequestMapping(value = "hello", method = RequestMethod.GET)
String sayHelloFromClient(@RequestParam(value = "name") String name);
}
第九步：实现HelloService类
HelloService需要实现sayHelloFromClient接口，并注入到Ioc容器中，代码如下，代码如下：
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import com.test.servicefeign.service.HelloService;
import org.springframework.stereotype.Component;
@Component
public class HelloServiceImpl implements HelloService {
@Override
public String sayHelloFromClient(String name) {
return "sorry " + name;
}
}
第十步：启动所有工程（不包含service-ribbon）
打开 http://localhost:9874/hello?name=handsomeman ，你会在浏览器上看到显示：
hello: handsomeman,i am from port:9872
当我们关闭eureka-client工程时，再次访问 http://localhost:9874/hello?name=handsomeman，浏览器会显示：
sorry handsomeman
这就说明断路器起作用了。
源码下载：
https://github.com/mochengyanliu/SpringCloudLearn/tree/master/section4
