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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <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

运行：localhost:8080/hello