在微服务架构中,根据业务需求拆分成一个个的微小服务,然后服务与服务之间可以相互RPC远程调用。在Spring Cloud可以使用RestTemplate+Ribbon或者Feign来进行RPC远程调用。为了保证服务高可用性,单个服务通常会进行集群部署。由于网络原因或者自身的原因,服务并不能保证百分之一百可用,如果服务方出现问题,调用这个服务就会出现线程阻塞,此时若有出现大量请求,导致服务方瘫痪。这时断路器就派上用场了。
11、RestTemplate+Ribbon整合断路器Hystrix
当对某个服务的调用的不可用达到一个阀值(Hystric 默认是5秒20次) 断路器将会被自动被打开。断路打开后, fallback方法可以直接返回一个预先设置的固定值。

1、 新建项目sc-eureka-client-consumer-ribbon-hystrix,对应的pom.xml文件

<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>spring-cloud</groupId>
    <artifactId>sc-eureka-client-consumer-ribbon</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>sc-eureka-client-consumer-ribbon</name>
    <url>http://maven.apache.org</url>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.4.RELEASE</version>
    </parent>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Finchley.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>

        </dependencies>
    </dependencyManagement>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <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-ribbon</artifactId> 
                    <version>1.4.5.RELEASE</version> 
            </dependency> -->

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
        </dependency>

        <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <!--        
        <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-hystrix</artifactId>
                <version>1.4.5.RELEASE</version>
        </dependency> -->

        <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
                <version>2.0.1.RELEASE</version>
        </dependency>

    </dependencies>
</project>

备注:spring-cloud-starter-hystrix已经在spring cloud 2.x标注成过期。推荐使用spring-cloud-starter-netflix-hystrix
11、RestTemplate+Ribbon整合断路器Hystrix
2、 新建spring boot 启动类ConsumerApplication.java

package sc.consumer;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.hystrix.EnableHystrix;

@SpringBootApplication
@EnableEurekaClient
@EnableHystrix
public class ConsumerHystrixApplication {

    public static void main(String[] args) {

        SpringApplication.run(ConsumerHystrixApplication.class, args);

    }

}

可以看出这个启动类只是《服务发现&服务消费者Ribbon》的启动类添加多了一个注解EnableHystrix(启动断路器)

3、 编写服务类,并添加断路器注解

package sc.consumer.service.impl;

import java.util.HashMap;
import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

import com.github.andrewoma.dexx.collection.ArrayList;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;

import sc.consumer.model.User;
import sc.consumer.service.UserService;

@Service
public class UserServiceImpl implements UserService{

    @Autowired
    private RestTemplate restTemplate;

    @HystrixCommand(fallbackMethod = "getUserError")
    @Override
    public Map<String, Object> getUser(Long id) {
        return restTemplate.getForObject("http://sc-eureka-client-provider:8200/user/getUser/{1}", Map.class, id);
    }

    public Map<String, Object> getUserError(Long id){
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("code", "000000");
        map.put("msg", "ok");
        User u = new User();
        u.setId(-1L);
        u.setUserName("failName");
        map.put("body", u);
        return map;
    }

    @HystrixCommand(fallbackMethod = "listUserError")
    @Override
    public Map<String, Object> listUser() {
        return restTemplate.getForObject("http://sc-eureka-client-provider:8200/user/listUser", Map.class);
    }

    public Map<String, Object> listUserError(){
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("code", "000000");
        map.put("msg", "ok");
        map.put("body", new ArrayList<User>());
        return map;
    }

    @HystrixCommand(fallbackMethod = "addUserError")
    @Override
    public Map<String, Object> addUser(User user) {
        return restTemplate.postForObject("http://sc-eureka-client-provider:8200/user/addUser", user, Map.class);
    }

    public Map<String, Object> addUserError(User user){
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("code", "000000");
        map.put("msg", "ok");
        map.put("body", 0);
        return map;
    }

    @HystrixCommand(fallbackMethod = "updateUserError")
    @Override
    public Map<String, Object> updateUser(User user) {
        restTemplate.put("http://sc-eureka-client-provider:8200/user/updateUser",user);
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("code", "000000");
        map.put("msg", "ok");
        return map;
    }

    public Map<String, Object> updateUserError(User user){
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("code", "000000");
        map.put("msg", "ok");
        map.put("body", 0);
        return map;
    }

    @HystrixCommand(fallbackMethod = "deleteUserError")
    @Override
    public Map<String, Object> deleteUser(Long id) {
        restTemplate.delete("http://sc-eureka-client-provider:8200/user/deleteUser/{id}", id);
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("code", "000000");
        map.put("msg", "ok");
        return map;
    }

    public Map<String, Object> deleteUserError(Long id){
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("code", "000000");
        map.put("msg", "ok");
        map.put("body", 0);
        return map;
    }

}

添加HystrixCommand注解,对应的参数fallbackMethod值为当方式服务方无法调用时,返回预设值得方法名。

4、 新建配置文件bootstrap.yml和application.yml
bootstrap.yml

server:
    port: 5600

application.yml

spring:
    application:
        name: sc-eureka-client-consumer-ribbon-hystrix

eureka:
    instance:
        hostname: 127.0.0.1
    client:
        #由于该应用为注册中心,所以设置为false,代表不向注册中心注册自己
        registerWithEureka: true
        #由于注册中心的职责就是维护服务实例,它并不需要去检索服务,所以也设置为false
        fetchRegistry: true
        serviceUrl:
            defaultZone: http://127.0.0.1:5001/eureka/

5、 其他项目文件参加下图

11、RestTemplate+Ribbon整合断路器Hystrix

6、 分别启动注册中心sc-eureka-server和服务提供者sc-eureka-client-provider

7、 启动sc-eureka-client-consumer-ribbon-hystrix,并验证是否启动成功
方式一:查看日志
11、RestTemplate+Ribbon整合断路器Hystrix

方式二:查看注册中心是否注册成功

11、RestTemplate+Ribbon整合断路器Hystrix
8、 验证断路器是否起作用
(1) 服务提供者正常时访问:
http://127.0.0.1:5600/cli/user/getUser/4
11、RestTemplate+Ribbon整合断路器Hystrix
正常返回数据库里的数据
(2) 服务提供者关闭时访问:
http://127.0.0.1:5600/cli/user/getUser/4
11、RestTemplate+Ribbon整合断路器Hystrix
对比两个返回的数据,可以看出服务提供者关闭时,返回的数据是在程序写死的数据,如下图:
11、RestTemplate+Ribbon整合断路器Hystrix
其他方法可以自行按照以上方式进行验证。

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