feign多服务间的调用
上文我们把我们项目注册到服务器上了，但是在微服务中，我们会有多个服务，同时也会使用A服务调用B服务的接口。springcloud netflix这里有两种方式ribbon和feign，我们分别介绍。
1.ribbon
ribbon说白了就是使用restTemplate。上文编写了被调用方的代码，下文将编写调用方的代码。
1.修改pom文件
<?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>2.2.5.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.baocl</groupId> <artifactId>eureka-consumer</artifactId> <version>0.0.1-SNAPSHOT</version> <name>eureka-consumer</name> <description>Demo project for Spring Boot</description> <properties> <java.version>1.8</java.version> <spring-cloud.version>Hoxton.SR1</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-ribbon</artifactId> </dependency> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> <exclusions> <exclusion> <groupId>org.junit.vintage</groupId> <artifactId>junit-vintage-engine</artifactId> </exclusion> </exclusions> </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> 复制代码2.修改Application
然后修改EurekaConsumerApplication类，需要在新建RestTemplate的bean。
import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.cloud.client.discovery.EnableDiscoveryClient; import org.springframework.cloud.client.loadbalancer.LoadBalanced; import org.springframework.context.annotation.Bean; import org.springframework.web.client.RestTemplate; @SpringBootApplication @EnableDiscoveryClient public class EurekaConsumerApplication { @Bean @LoadBalanced // ribbon注解 public RestTemplate restTemplate() { return new RestTemplate(); } public static void main(String[] args) { SpringApplication.run(EurekaConsumerApplication.class, args); } } 复制代码3.新建调用方接口DcController
新建普通接口，调用上文被调用方的服务。
import org.springframework.beans.factory.annotation.Autowired; import org.springframework.cloud.client.discovery.DiscoveryClient; import org.springframework.cloud.client.loadbalancer.LoadBalancerClient; import org.springframework.http.ResponseEntity; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; import org.springframework.web.client.RestTemplate; @RestController @RequestMapping("/eureka1") public class DcController { @Autowired LoadBalancerClient loadBalancerClient; @Autowired RestTemplate restTemplate; @Autowired DiscoveryClient discoveryClient; @GetMapping("/consumer") public ResponseEntity<String> dc() { //String url = "http://eureka-client/aaa/dc?dk=3001"; String url = "http://EUREKA-CLIENT/aaa/dc?dk=3001"; System.out.println(url); // ServiceInstance serviceInstance = // loadBalancerClient.choose("eureka-client");// 获取服务提供者信息 // // String url = "http://localhost:" + serviceInstance.getPort() + "/aaa/dc"; // System.out.println(serviceInstance.getPort() ); // System.out.println(url); // ResponseEntity r = restTemplate.getForEntity("http://eureka-client/aaa/dc", // String.class); // System.out.println("r.getHeaders().getHost():"+r.getHeaders().getHost()); // System.out.println("r.getHeaders().getLocation():"+r.getHeaders().getLocation()); // System.out.println("r.getHeaders().getOrigin():"+r.getHeaders().getOrigin()); return restTemplate.getForEntity(url, String.class); // ribbon应用 } } 复制代码有一个坑 在调用时候需要String url = "http://eureka-client/aaa/dc?dk=3001"，而不是String url ="http://localhost:2002/aaa/dc?dk=3001"，否则会报错java.lang.IllegalStateException: No instances available for localhost.
4.修改application
最后是配置文件application.yml，这里我们使用.yml文件，都是基础配置。
eureka: client: registery-fetch-interval-seconds: 5000 serviceUrl: defaultZone: http://localhost:1001/eureka/ eureka-client: ribbon: NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RandomRule server: port: 3001 spring: application: name: eureka-consumer 复制代码
输入http://localhost:3001/eureka1/consumer 就可以调用到上文的client服务了，同时还可以配置负载均衡策略。在NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RandomRule 处配置。
2.feign
1.修改pom文件
<?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>2.2.5.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.baocl</groupId> <artifactId>eureka-consumer-feign</artifactId> <version>0.0.1-SNAPSHOT</version> <name>eureka-consumer-feign</name> <description>Demo project for Spring Boot</description> <properties> <java.version>1.8</java.version> <spring-cloud.version>Hoxton.SR1</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-feign</artifactId> <version>1.4.7.RELEASE</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> <exclusions> <exclusion> <groupId>org.junit.vintage</groupId> <artifactId>junit-vintage-engine</artifactId> </exclusion> </exclusions> </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> 复制代码版本问题一定要控制！！！！这里有一个坑 就是版本问题，有时会报错
org.springframework.beans.factory.BeanDefinitionStoreException: Failed to read candidate component class: file [F:\workspace\springcloud\tse9\eureka-consumer-feign\target\classes\com\cloud\DcClient.class]; nested exception is org.springframework.core.annotation.AnnotationConfigurationException: Attribute 'value' in annotation [org.springframework.cloud.netflix.feign.FeignClient] must be declared as an @AliasFor 'serviceId', not 'name'. 复制代码
解决办法可以参考：www.pianshen.com/article/223…
2.修改EurekaConsumerFeignApplication
首先在EurekaConsumerFeignApplication使用@EnableFeignClients中开启feign
import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.cloud.client.discovery.EnableDiscoveryClient; import org.springframework.cloud.openfeign.EnableFeignClients; @EnableFeignClients @EnableDiscoveryClient @SpringBootApplication public class EurekaConsumerFeignApplication { public static void main(String[] args) { SpringApplication.run(EurekaConsumerFeignApplication.class, args); } } 复制代码3.新建接口DcClient
新建一个接口DcClient，配置调用其他服务的名称和接口名称。（被调用方客户端的服务与接口信息）
import org.springframework.cloud.openfeign.FeignClient; import org.springframework.web.bind.annotation.GetMapping; @FeignClient(name = "eureka-client") public interface DcClient { @GetMapping("/aaa/dc?dk=3002") String consumer(); @GetMapping("/aaa/dc?dk=3002") String consumer2(); } 复制代码4.新建调用接口DcController
业务接口的书写，同时注入dcClient调用其他服务。
import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; import com.cloud.DcClient; @RestController @RequestMapping("/eureka2") public class DcController { @Autowired DcClient dcClient; @GetMapping("/consumer") public String dc() { return dcClient.consumer(); } } 复制代码5.修改application.properties
下文是最基础的配置。
spring.application.name=eureka-consumer-feign server.port=3002 eureka.client.serviceUrl.defaultZone=http://localhost:1001/eureka/ 复制代码
然后调用http://localhost:3002/eureka2/consumer 可以发现接口掉通了 ，在被调用方也有相应的日志。
3.ribbon和Eureka整合原理
基本流程就是 客户端从eureka中获取到缓存的服务列表，获取到目的服务的信息，然后通过自身的负载均衡策略，去调用对应的服务。
1.负载均衡策略
BestAvailableRule 选择一个最小的并发请求的server。
AvailabilityFilteringRule 过滤掉那些因为一直连接失败的被标记为circuit tripped的后端server，并过滤掉那些高并发的的后端server（active connections 超过配置的阈值）。
WeightedResponseTimeRule 根据响应时间分配一个weight，响应时间越长，weight越小，被选中的可能性越低。
RetryRule 对选定的负载均衡策略机上重试机制。
RoundRobinRule roundRobin方式轮询选择server.。
RandomRule 随机选择一个server。
ZoneAvoidanceRule 复合判断server所在区域的性能和server的可用性选择server。
作者：小黄鸡1992
链接：https://juejin.cn/post/7022429183842189320