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 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

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!"