SpringCloud之Hystrix：集群容错框架

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分布式环境中，可能会有一些被依赖的服务会失效，影响系统的稳定运行。
Hystrix通过添加延迟阈值以及容错的逻辑，以控制分布式系统间组件的交互。
Hystrix通过隔离服务间的访问点、停止它们之间的级联故障、提供可回退操作来实现容错。

下面例子为在Spring Cloud的使用。
开发工具：IntelliJ IDEA 2019.2.3

一、服务器端

1、创建项目

IDEA中创建一个新的SpringBoot项目，名称为“spring-hystrix-server”，SpringBoot版本选择2.1.10，在选择Dependencies(依赖)的界面勾选Spring Cloud Discovery ->
Eureka Server，创建完成后的pom.xml配置文件自动添加SpringCloud最新稳定版本依赖，当前为Greenwich.SR3。
pom.xml完整内容如下：

<?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 https://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>2.1.10.RELEASE</version>

        <relativePath/> <!-- lookup parent from repository -->

    </parent>

    <groupId>com.example</groupId>

    <artifactId>spring-hystrix-server</artifactId>

    <version>0.0.1-SNAPSHOT</version>

    <name>spring-hystrix-server</name>

    <description>Demo project for Spring Boot</description>

    <properties>

        <java.version>1.8</java.version>

        <spring-cloud.version>Greenwich.SR3</spring-cloud.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>org.springframework.cloud</groupId>

            <artifactId>spring-cloud-starter-netflix-eureka-server</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application.yml

修改端口号为8761；取消将自己信息注册到Eureka服务器，不从Eureka服务器抓取注册信息。

server:

  port: 8761

eureka:

  client:

    register-with-eureka: false

    fetch-registry: false

3、修改启动类代码

增加注解@EnableEurekaServer

二、服务提供者

1、创建项目

IDEA中创建一个新的SpringBoot项目，除了名称为“spring-hystrix-provider”，其它步骤和上面创建服务器端一样。

2、修改配置application.yml

server:

  port: 8080

spring:

  application:

    name: spring-hystrix-provider

eureka:

  instance:

    hostname: localhost

  client:

    serviceUrl:

      defaultZone: http://localhost:8761/eureka/

3、添加一个实体类User.java

package com.example.springhystrixprovider;

public class User {

    String name;

    Integer age;

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public Integer getAge() {

        return age;

    }

    public void setAge(Integer age) {

        this.age = age;

    }

}

4、修改启动类代码

package com.example.springhystrixprovider;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.cloud.netflix.eureka.EnableEurekaClient;

import org.springframework.http.MediaType;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;

@SpringBootApplication

@EnableEurekaClient

@RestController

public class SpringHystrixProviderApplication {

    public static void main(String[] args) {

        SpringApplication.run(SpringHystrixProviderApplication.class, args);

    }

    @RequestMapping("/hello")

    public String hello(HttpServletRequest request) {

        return "hello world." + request.getServerPort();

    }

    @RequestMapping(value="/user/{name}", produces = MediaType.APPLICATION_JSON_VALUE)

    public User user(@PathVariable String name) {

        User u = new User();

        u.setName(name);

        u.setAge(30);

        return u;

    }

}

三、服务调用者

1、创建项目

IDEA中创建一个新的SpringBoot项目，名称为“spring-hystrix-invoker”，SpringBoot版本选择2.1.10，在选择Dependencies(依赖)的界面勾选Spring Cloud Discovery -> Eureka Server，Spring Cloud Circuit Breaker -> Hystrix。
pom.xml完整内容如下：

<?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 https://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>2.1.10.RELEASE</version>

        <relativePath/> <!-- lookup parent from repository -->

    </parent>

    <groupId>com.example</groupId>

    <artifactId>spring-hystrix-invoker</artifactId>

    <version>0.0.1-SNAPSHOT</version>

    <name>spring-hystrix-invoker</name>

    <description>Demo project for Spring Boot</description>

    <properties>

        <java.version>1.8</java.version>

        <spring-cloud.version>Greenwich.SR3</spring-cloud.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>org.springframework.cloud</groupId>

            <artifactId>spring-cloud-starter-netflix-eureka-server</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application.yml

server:

  port: 9000

spring:

  application:

    name: spring-hystrix-invoker

eureka:

  instance:

    hostname: localhost

  client:

    serviceUrl:

      defaultZone: http://localhost:8761/eureka/

3、修改启动类代码

增加注解@EnableEurekaClient和@EnableCircuitBreaker。

package com.example.springhystrixinvoker;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.boot.web.servlet.ServletComponentScan;

import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;

import org.springframework.cloud.client.loadbalancer.LoadBalanced;

import org.springframework.cloud.netflix.eureka.EnableEurekaClient;

import org.springframework.context.annotation.Bean;

import org.springframework.web.client.RestTemplate;

@SpringBootApplication

@EnableEurekaClient

@EnableCircuitBreaker

public class SpringHystrixInvokerApplication {

    @LoadBalanced

    @Bean

    public RestTemplate getRestTemplate(){

        return new RestTemplate();

    }

    public static void main(String[] args) {

        SpringApplication.run(SpringHystrixInvokerApplication.class, args);

    }

}

4、添加一个实体类User.java

package com.example.springhystrixinvoker;

public class User {

    String name;

    Integer age;

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public Integer getAge() {

        return age;

    }

    public void setAge(Integer age) {

        this.age = age;

    }

}

5、添加一个服务类，在服务方法中调用服务

服务方法用@HystrixCommand注解进行修饰，并配置了回退方法。

package com.example.springhystrixinvoker;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Component;

import org.springframework.web.client.RestTemplate;

@Component

public class UserService {

    @Autowired

    private RestTemplate restTemplate;

    @HystrixCommand(fallbackMethod = "getUserFallback")

    public User getUser(String name){

        User user = restTemplate.getForObject("http://spring-hystrix-provider/user/{name}", User.class, name);

        return user;

    }

    public User getUserFallback(String name){

        User user = new User();

        user.setName("无名");

        user.setAge(20);

        return user;

    }

}

6、添加控制器 InvokerController.java

package com.example.springhystrixinvoker;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.http.MediaType;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

import org.springframework.web.bind.annotation.RestController;

@RestController

public class InvokerController {

    @Autowired

    private UserService userService;

    @RequestMapping(value = "/invokeUser/{name}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)

    public User invokeUser(@PathVariable String name){

        User user = userService.getUser(name);

        return user;

    }

}

四、测试

1、启动服务器端。
浏览器访问http://localhost:8761/，正常
2、启动服务提供者
浏览器访问 http://localhost:8080/user/小明
页面输出：{"name":"小明","age":30}
3、启动服务调用者。
浏览器访问http://localhost:9000/invokeUser/小明
页面输出：{"name":"小明","age":30}
4、停止8080服务提供者，再访问9000地址
页面输出：{"name":"无名","age":20}
由此可见，由于调用失败，触发了回退方法。

五、缓存注解

Hystrix支持缓存功能，如果在 一次请求过程 中，多个地方调用同一个接口，可以考虑使用缓存。
缓存可以通过注解实现，缓存与合并请求功能需要先初始化请求上下文才能实现。

1、新建一个javax.servlet.Filter，用于创建与销毁Hystrix的请求上下文

package com.example.springhystrixinvoker;

import com.netflix.hystrix.strategy.concurrency.HystrixRequestContext;

import javax.servlet.*;

import javax.servlet.annotation.WebFilter;

import java.io.IOException;

@WebFilter(urlPatterns = "/*", filterName = "hystrixFilter")

public class HystrixFilter implements Filter {

    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest request, ServletResponse response,

                         FilterChain chain) throws IOException, ServletException {

        HystrixRequestContext context = HystrixRequestContext.initializeContext();

        try{

            chain.doFilter(request,response);

        }finally {

            context.shutdown();

        }

    }

    public void destroy() {

    }

}

2、在启动类中加入注解 @ServletComponentScan

3、编写服务方法，使用缓存注解

（1）@CacheResult 被修饰的方法返回结果会被缓存，和@HystrixCommand搭配
（2）@CacheRemove 让缓存失效
（3）@CacheKey 修饰方法参数，表示该参数作为缓存的key

package com.example.springhystrixinvoker;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;

import com.netflix.hystrix.contrib.javanica.cache.annotation.CacheRemove;

import com.netflix.hystrix.contrib.javanica.cache.annotation.CacheResult;

import org.springframework.stereotype.Component;

@Component

public class CacheService {

    @CacheResult

    @HystrixCommand(commandKey = "removeKey")

    public String cacheMethod(String name){

        System.out.println("执行cacheMethod方法");

        return "hello";

    }

    @CacheRemove(commandKey = "removeKey")

    @HystrixCommand(commandKey = "removeKey")

    public String updateMethod(String name){

        System.out.println("执行updateMethod方法");

        return "update";

    }

}

4、控制器中调用

浏览器访问：http://localhost:9000/cacheMethod，IDEA控制台输出：

控制器调用服务：0

执行cacheMethod方法

控制器调用服务：1

控制器调用服务：2

控制器调用服务：3

控制器调用服务：4

控制器调用服务：5

执行updateMethod方法

控制器调用服务：6

执行cacheMethod方法

控制器调用服务：7

控制器调用服务：8

控制器调用服务：9

六、Feign与Hystrix整合

修改服务调用者项目的代码
1、pom.xml加入Feign依赖

        <dependency>

            <groupId>org.springframework.cloud</groupId>

            <artifactId>spring-cloud-starter-openfeign</artifactId>

        </dependency>

2、修改配置application.yml

增加下面配置：打开Feign的Hystrix的配置

feign:

  hystrix:

    enabled: true

3、启动类加上注解@EnableFeignClients

4、新建Feign接口

package com.example.springhystrixinvoker;

import org.springframework.cloud.openfeign.FeignClient;

import org.springframework.stereotype.Component;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

//指定调用的服务名称

@FeignClient(name="spring-hystrix-provider", fallback = UserClient.UserClientFallback.class)

public interface UserClient {

    @RequestMapping(method = RequestMethod.GET, value = "/user/{name}")

    User getUser(@PathVariable("name") String name);

    @Component

    static class UserClientFallback implements UserClient{

        public User getUser(String name){

            User user = new User();

            user.setName("无名");

            user.setAge(20);

            return user;

        }

    }

}

5、控制器InvokerController，添加代码

    @Autowired

    private UserClient userClient;

    @RequestMapping(value = "/invokeUser2/{name}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)

    public User invokeUser2(@PathVariable String name){

        User user = userClient.getUser(name);

        return user;

    }