在一个分布式系统里，许多依赖不可避免的会调用失败，比如超时、异常等，如何能够保证在一个依赖出问题的情况下，不会导致整体服务失败，这个就是Hystrix需要做的事情。Hystrix提供了熔断、隔离、Fallback、cache、监控等功能，能够在一个、或多个依赖同时出现问题时保证系统依然可用。

在分布式系统架构中多个系统之间通常是通过远程RPC调用进行通信，也就是 A 系统调用 B 系统服务，B 系统调用 C 系统的服务。当尾部应用 C 发生故障而系统 B 没有服务降级时候可能会导致 B，甚至系统 A 瘫痪，这种现象被称为雪崩现象。所以在系统设计时候要使用一定的降级策略，来保证当服务提供方服务不可用时候，服务调用方可以切换到降级后的策略进行执行。

  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  3.     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  4.     <modelVersion>4.0.0</modelVersion>
  6.     <groupId>com.xm.cloud</groupId>
  7.     <artifactId>cl_hello_consumer_hy</artifactId>
  8.     <version>0.0.1-SNAPSHOT</version>
  9.     <packaging>jar</packaging>
  11.     <name>cl_hello_consumer_hy</name>
  12.     <description>This is a Web about springcloud</description>
  14.     <parent>
  15.         <groupId>org.springframework.boot</groupId>
  16.         <artifactId>spring-boot-starter-parent</artifactId>
  17.         <version>2.0.6.RELEASE</version>
  18.         <relativePath/> <!-- lookup parent from repository -->
  19.     </parent>
  21.     <properties>
  22.         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  23.         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
  24.         <java.version>1.8</java.version>
  25.         <spring-cloud.version>Finchley.SR2</spring-cloud.version>
  26.     </properties>
  28.     <dependencies>
  29.         <dependency>
  30.             <groupId>org.springframework.boot</groupId>
  31.             <artifactId>spring-boot-starter-web</artifactId>
  32.         </dependency>
  33.         <dependency>
  34.             <groupId>org.springframework.cloud</groupId>
  35.             <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
  36.         </dependency>
  37.         <dependency>
  38.             <groupId>org.springframework.cloud</groupId>
  39.             <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
  40.         </dependency>
  41.         <dependency>
  42.             <groupId>org.springframework.cloud</groupId>
  43.             <artifactId>spring-cloud-starter-openfeign</artifactId>
  44.         </dependency>
  46.         <dependency>
  47.             <groupId>org.springframework.boot</groupId>
  48.             <artifactId>spring-boot-starter-test</artifactId>
  49.             <scope>test</scope>
  50.         </dependency>
  51.         <dependency>
  52.             <groupId>org.springframework.boot</groupId>
  53.             <artifactId>spring-boot-starter-actuator</artifactId>
  54.         </dependency>
  55.     </dependencies>
  57.     <dependencyManagement>
  58.         <dependencies>
  59.             <dependency>
  60.                 <groupId>org.springframework.cloud</groupId>
  61.                 <artifactId>spring-cloud-dependencies</artifactId>
  62.                 <version>${spring-cloud.version}</version>
  63.                 <type>pom</type>
  64.                 <scope>import</scope>
  65.             </dependency>
  66.         </dependencies>
  67.     </dependencyManagement>
  69.     <build>
  70.         <plugins>
  71.             <plugin>
  72.                 <groupId>org.springframework.boot</groupId>
  73.                 <artifactId>spring-boot-maven-plugin</artifactId>
  74.             </plugin>
  75.         </plugins>
  76.     </build>
  79. </project>
  1. eureka.client.service-url.defaultZone=http://127.0.0.1:7001/eureka/
  3. eureka.client.register-with-eureka=false
  5. feign.hystrix.enabled=true
  1. package com.xm.cloud;
  3. import org.springframework.boot.SpringApplication;
  4. import org.springframework.boot.autoconfigure.SpringBootApplication;
  5. import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
  6. import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
  7. import org.springframework.cloud.openfeign.EnableFeignClients;
  9. @EnableDiscoveryClient
  10. @EnableFeignClients
  11. @SpringBootApplication
  12. public class ClHelloConsumerHyApplication {
  14.     public static void main(String[] args) {
  15.         SpringApplication.run(ClHelloConsumerHyApplication.class, args);
  16.     }
  17. }
  1. package com.xm.cloud.fallback;
  3. import org.springframework.stereotype.Component;
  5. import com.xm.cloud.service.HelloService;
  7. import feign.hystrix.FallbackFactory;
  9. @Component
  10. public class HelloServiceFallbackFactory implements FallbackFactory<HelloService> {
  12.     @Override
  13.     public HelloService create(Throwable cause) {
  14.         return new HelloService() {
  15.             
  16.             @Override
  17.             public String sayHello() {
  18.                 return "HelloService 异常！";
  19.             }
  20.         };
  21.     }
  23. }
  1. package com.xm.cloud.service;
  3. import org.springframework.cloud.openfeign.FeignClient;
  4. import org.springframework.web.bind.annotation.GetMapping;
  6. import com.xm.cloud.fallback.HelloServiceFallbackFactory;
  8. @FeignClient(value="CL-HELLO-PRODUCER",fallbackFactory=HelloServiceFallbackFactory.class)
  9. public interface HelloService {
  10.     
  11.     @GetMapping("/hello")
  12.     public String sayHello();
  14. }
  1. package com.xm.cloud.controller;
  3. import java.util.ArrayList;
  4. import java.util.List;
  6. import org.springframework.beans.factory.annotation.Autowired;
  7. import org.springframework.web.bind.annotation.GetMapping;
  8. import org.springframework.web.bind.annotation.RestController;
  10. import com.xm.cloud.service.HelloService;
  12. @RestController
  13. public class HelloController {
  14.     
  15.     @Autowired
  16.     private HelloService helloService;
  17.     
  18.     @GetMapping("/hello")
  19.     public List<String> sayHello() {
  20.         List<String> list = new ArrayList<String>();
  21.         for(int i=0;i<10;i++) {
  22.             list.add(helloService.sayHello());
  23.         }
  24.         return list;
  25.     }
  27. }
  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  3.     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  4.     <modelVersion>4.0.0</modelVersion>
  6.     <groupId>com.xm.cloud</groupId>
  7.     <artifactId>cl_hello_producer_hy</artifactId>
  8.     <version>0.0.1-SNAPSHOT</version>
  9.     <packaging>jar</packaging>
  11.     <name>cl_hello_producer_hy</name>
  12.     <description>This is a Web about springcloud</description>
  14.     <parent>
  15.         <groupId>org.springframework.boot</groupId>
  16.         <artifactId>spring-boot-starter-parent</artifactId>
  17.         <version>2.0.6.RELEASE</version>
  18.         <relativePath/> <!-- lookup parent from repository -->
  19.     </parent>
  21.     <properties>
  22.         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  23.         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
  24.         <java.version>1.8</java.version>
  25.         <spring-cloud.version>Finchley.SR2</spring-cloud.version>
  26.     </properties>
  28.     <dependencies>
  29.         <dependency>
  30.             <groupId>org.springframework.boot</groupId>
  31.             <artifactId>spring-boot-starter-web</artifactId>
  32.         </dependency>
  33.         <dependency>
  34.             <groupId>org.springframework.cloud</groupId>
  35.             <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
  36.         </dependency>
  37.         <dependency>
  38.             <groupId>org.springframework.cloud</groupId>
  39.             <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
  40.         </dependency>
  42.         <dependency>
  43.             <groupId>org.springframework.boot</groupId>
  44.             <artifactId>spring-boot-starter-test</artifactId>
  45.             <scope>test</scope>
  46.         </dependency>
  47.     </dependencies>
  49.     <dependencyManagement>
  50.         <dependencies>
  51.             <dependency>
  52.                 <groupId>org.springframework.cloud</groupId>
  53.                 <artifactId>spring-cloud-dependencies</artifactId>
  54.                 <version>${spring-cloud.version}</version>
  55.                 <type>pom</type>
  56.                 <scope>import</scope>
  57.             </dependency>
  58.         </dependencies>
  59.     </dependencyManagement>
  61.     <build>
  62.         <plugins>
  63.             <plugin>
  64.                 <groupId>org.springframework.boot</groupId>
  65.                 <artifactId>spring-boot-maven-plugin</artifactId>
  66.             </plugin>
  67.         </plugins>
  68.     </build>
  71. </project>
  1. server.port=8001
  2. spring.application.name=cl-hello-producer
  4. eureka.client.service-url.defaultZone=http://127.0.0.1:7001/eureka/
  1. package com.xm.cloud;
  3. import org.springframework.boot.SpringApplication;
  4. import org.springframework.boot.autoconfigure.SpringBootApplication;
  5. import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
  6. import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
  8. @EnableDiscoveryClient
  9. @EnableCircuitBreaker
  10. @SpringBootApplication
  11. public class ClHelloProducerHyApplication {
  13.     public static void main(String[] args) {
  14.         SpringApplication.run(ClHelloProducerHyApplication.class, args);
  15.     }
  16. }
  1. package com.xm.cloud.controller;
  3. import org.springframework.web.bind.annotation.GetMapping;
  4. import org.springframework.web.bind.annotation.RestController;
  6. import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
  8. @RestController
  9. public class HelloController {
  10.     
  11.     @GetMapping("/hello")
  12.     @HystrixCommand
  13.     public String sayHello() {
  14.         
  15.         if(Math.random()>0.5) {
  16.             throw new RuntimeException();
  17.         } else {
  18.             return "Hello spring cloud!";
  19.         }
  20.     }
  22. }

运行：localhost:8080/hello

0 “HelloService 异常！”
1 “Hello spring cloud!”
2 “HelloService 异常！”
3 “Hello spring cloud!”
4 “Hello spring cloud!”
5 “Hello spring cloud!”
6 “Hello spring cloud!”
7 “Hello spring cloud!”
8 “HelloService 异常！”
9 “Hello spring cloud!”

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本文链接：https://www.cnblogs.com/TimerHotel/p/springcloud_05.html