5.Spring Cloud初相识-------Hystrix熔断器

前言： 1.介绍Hystrix

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。

2.为什么使用Hystrix

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。

实战： 1.新建服务消费者： （1）添加依赖 <?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 "> <modelVersion>4.0.0</modelVersion> <groupId>com.xm.cloud</groupId> <artifactId>cl_hello_consumer_hy</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>cl_hello_consumer_hy</name> <description>This is a Web about springcloud</description> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.0.6.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> <spring-cloud.version>Finchley.SR2</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-openfeign</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-actuator</artifactId> </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> </project> （2）修改配置 eureka.client.service-url.defaultZone=http://127.0.0.1:7001/eureka/ eureka.client.register-with-eureka=false feign.hystrix.enabled=true （3）开启注解 package com.xm.cloud; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker; import org.springframework.cloud.client.discovery.EnableDiscoveryClient; import org.springframework.cloud.openfeign.EnableFeignClients; @EnableDiscoveryClient @EnableFeignClients @SpringBootApplication public class ClHelloConsumerHyApplication { public static void main(String[] args) { SpringApplication.run(ClHelloConsumerHyApplication.class, args); } } （4）配置熔断回调工厂 package com.xm.cloud.fallback; import org.springframework.stereotype.Component; import com.xm.cloud.service.HelloService; import feign.hystrix.FallbackFactory; @Component public class HelloServiceFallbackFactory implements FallbackFactory<HelloService> { @Override public HelloService create(Throwable cause) { return new HelloService() { @Override public String sayHello() { return "HelloService 异常！"; } }; } } （5）新建Service package com.xm.cloud.service; import org.springframework.cloud.openfeign.FeignClient; import org.springframework.web.bind.annotation.GetMapping; import com.xm.cloud.fallback.HelloServiceFallbackFactory; @FeignClient(value="CL-HELLO-PRODUCER",fallbackFactory=HelloServiceFallbackFactory.class) public interface HelloService { @GetMapping("/hello") public String sayHello(); } （6）新建Controller package com.xm.cloud.controller; import java.util.ArrayList; import java.util.List; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; import com.xm.cloud.service.HelloService; @RestController public class HelloController { @Autowired private HelloService helloService; @GetMapping("/hello") public List<String> sayHello() { List<String> list = new ArrayList<String>(); for(int i=0;i<10;i++) { list.add(helloService.sayHello()); } return list; } } 2.新建服务提供者： （1）添加依赖 <?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 "> <modelVersion>4.0.0</modelVersion> <groupId>com.xm.cloud</groupId> <artifactId>cl_hello_producer_hy</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>cl_hello_producer_hy</name> <description>This is a Web about springcloud</description> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.0.6.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> <spring-cloud.version>Finchley.SR2</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.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> </project> （2）修改配置 server.port=8001 spring.application.name=cl-hello-producer eureka.client.service-url.defaultZone=http://127.0.0.1:7001/eureka/ （3）开启注解 package com.xm.cloud; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker; import org.springframework.cloud.client.discovery.EnableDiscoveryClient; @EnableDiscoveryClient @EnableCircuitBreaker @SpringBootApplication public class ClHelloProducerHyApplication { public static void main(String[] args) { SpringApplication.run(ClHelloProducerHyApplication.class, args); } } （4）新建Controller package com.xm.cloud.controller; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand; @RestController public class HelloController { @GetMapping("/hello") @HystrixCommand public String sayHello() { if(Math.random()>0.5) { throw new RuntimeException(); } else { return "Hello spring cloud!"; } } } 3.测试