Spring Cloud Feign 示例笔记

Feign是一个声明性web服务客户端，它使得编写web服务客户端变得更加容易，Spring Cloud Feign是基于Netflix Feign实现，整合了Spring Cloud Ribbon与Spring Cloud Hystrix,除了提供两者强大功能外，它还提供了声明式的Web服务客户端定义方式

1.Feign和OpenFeign的区别是什么

Feign是Spring Cloud组件中一个轻量级RESTful的HTTP服务客户端，Feign内置了Ribbon，用来做客户端负载均衡，去调用服务注册中心的服务。Feign的使用方式是：使用Feign的注解定义接口，调用接口，就可以调用服务注册中心的服务

引入依赖

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

OpenFeign是Spring Cloud在Feign的基础上支持了SpringMVC的注解，如@RequestMapping等等。OpenFeign的@FeignClient可以解析SpringMVC的@RequestMapping注解下的接口，并通过动态代理的方式产生实现类

引入依赖

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

参考代码： GitHub - PNZBEIJINGL/spring-cloud-lab

服务	IP	端口
eureka-peer	127.0.0.1	1000	Eureka服务注册中心
feign-consumer	127.0.0.1	8003	消费服务（测试Feign调用使用）
ms-customer	127.0.0.1	8001	客户服务
ms-customer_interface			客户接口工程

2.使用feign实现负载均衡

2.1修改ms-customer_interface应用

ms-customer_interface 中创建接口


@RequestMapping("/customer")
public interface ICustomerService {

    //测试
    @RequestMapping("/ping")
    public String ping();

    //根据ID获取客户信息
    @RequestMapping(value = "/get/{id}", method = RequestMethod.GET)
    public CustomerDTO getCustomerById(@PathVariable("id") Long id) throws InterruptedException;
    
    //保存客户信息
    @RequestMapping(value = "/save", method = RequestMethod.POST)
    public CustomerDTO addCustomer(@RequestBody CustomerDTO customerDTO) throws InterruptedException;
}

2.2 修改ms-customer应用

.ms-customer 应用中实现接口

@RestController
public class TestController implements ICustomerService {

    @Override
    public String ping() {
        //通过返回当前时间表明服务正常
        return new Date().toString();
    }

    @Override
    public CustomerDTO getCustomerById(@PathVariable("id") Long id) throws InterruptedException {
        //测试阻塞几秒
        int sleepTime = new Random().nextInt(3000);
        Thread.sleep(sleepTime);

        CustomerDTO customer = mockCustomer();//模拟得到一个客户
        customer.setId(id);
        return customer;
    }

    @Override
    public CustomerDTO addCustomer(@RequestBody CustomerDTO customerDTO) throws InterruptedException {
        //测试阻塞几秒
        int sleepTime = new Random().nextInt(3000);
        Thread.sleep(sleepTime);

        CustomerDTO customer = customerDTO;
        return customer;
    }

    private CustomerDTO mockCustomer() {
        CustomerDTO customer = new CustomerDTO();
        customer.setId(1000L);
        customer.setCode("1000");
        customer.setName("zhangsan");
        return customer;
    }
}

2.3修改feign-consumer应用

feign-consumer应用的pom.xml配置增加依赖，并设置application.properties配置

<dependencies>

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

        <!-- 注册服务提供 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
        </dependency>
        
        <!-- 引用Feign -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
            <version>1.3.6.RELEASE</version>
        </dependency>
       
        <!-- 引用监控-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

        <!-- 引用customer-intderface中年的接口-->
        <dependency>
            <groupId>spring.cloud.test</groupId>
            <artifactId>ms-customer-interface</artifactId>
            <version>1.0.0</version>
        </dependency>

    </dependencies>

server.port=8003
#服务的名称
spring.application.name=FEIGN-CONSUMER

############ Eureka ################
#服务注册中心IP
eureka.instance.hostname=127.0.0.1
#指定服务注册中心
eureka.client.serviceUrl.defaultZone=http://${eureka.instance.hostname}:1000/eureka/
############ Eureka ################

############ Feign ################
#Spring Cloud feign 中默认实现了请求重试机制
#重试策略先尝试首选实例N次
MS-CUSTOMER.ribbon.MaxAutoRetriesNextServer=1
#尝试更换N次实例进行重试
MS-CUSTOMER.ribbon.MaxAutoRetriesr=2
############ ribbon ################

feign-consumer应用主类增加@EnableFeignClients

@EnableFeignClients  //开启Spring Cloud Feign支持
@EnableDiscoveryClient
@SpringBootApplication
public class FeignConsumerApplication {

    public static void main(String[] args) {
        SpringApplication.run(FeignConsumerApplication.class, args);
    }

}

feign-consumer 创建RefactorCustomerService 接口继承接口ICusotmerService,通过@FeignClient注解指定服务名来绑定服务，这里服务名不区分大小写

@FeignClient("MS-CUSTOMER")
public interface RefactorCustomerService extends ICustomerService {

}

feign-consumer 创建RefactorCustomerController用于测试Feign客户端调用，Controller都通过RefactorCustomerService 接口调用实现


@RestController
public class RefactorCustomerController {

    @Autowired
    private RefactorCustomerService refactorHelloService;

    //http://127.0.0.1:8003/pingcustomer
    @RequestMapping(value = "/pingcustomer", method = RequestMethod.GET)
    public String pingCustomer() {
        return refactorHelloService.ping();
    }

    //http://127.0.0.1:8003/getcustomer
    @RequestMapping(value = "/getcustomer", method = RequestMethod.GET)
    public CustomerDTO getCustomer() {
        try {
            return refactorHelloService.getCustomerById(800L);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

    @RequestMapping(value = "/savecustomer", method = RequestMethod.GET)
    public CustomerDTO saveCustomer() {
        try {
            CustomerDTO customer = new CustomerDTO();
            customer.setId(70L);
            customer.setCode("70");
            customer.setName("zhangsan");
            return refactorHelloService.addCustomer(customer);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

}

2.4 测试feign-consumer中的Feign调用

启动eureka-peer 服务中心，
启动ms-customer服务后ms-customer服务注册到eureka中，
启动feign-consumer 服务
测试

测试访问：http://127.0.0.1:1000/ 检查好服务注册成功

测试： http://127.0.0.1:8003/pingcustomer

测试：http://127.0.0.1:8003/getcustomer

测试： http://127.0.0.1:8003/savecustomer

如果启动多个ms-customer服务时，多次访问会发现效果和Spring Cloud Ribbon相同，Feign实现的消费者维护了MS-CUSTOMER服务列表，通过轮询实现了客户端负载均衡，和Ribbon实现负载均衡相比，Feigin实现负载均衡通过定义服务绑定接口，以声明式的方法实现服务调用更简单

2.4 调用客户端时序图

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