Eureka 与 Feign 知识解析

1. Eureka

Spring Cloud Eureka 是服务发现组件，包含：

• Eureka Server：注册中心，管理服务实例
• Eureka Client：服务实例，向注册中心注册/获取服务信息

核心功能：

• 服务注册与发现
• 心跳检测（默认30秒）
• 服务故障自动剔除
• 客户端缓存注册信息

2. OpenFeign

声明式 HTTP 客户端工具，核心特性：

• 基于接口的声明式调用
• 整合 Ribbon 实现负载均衡
• 整合 Hystrix 实现熔断（需额外配置）
• 自动处理 HTTP 请求/响应序列化

依赖关系

<!-- Eureka Server -->
<dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency><!-- Eureka Client + OpenFeign -->
<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-openfeign</artifactId>
</dependency>

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完整示例代码

1. Eureka Server (服务注册中心)

application.yml

server:port: 8761
eureka:client:register-with-eureka: falsefetch-registry: false

EurekaServerApplication.java

@SpringBootApplication
@EnableEurekaServer
public class EurekaServerApplication {public static void main(String[] args) {SpringApplication.run(EurekaServerApplication.class, args);}
}

2. Service Provider (服务提供者)

application.yml

server:port: 8081
spring:application:name: user-service
eureka:client:service-url:defaultZone: http://localhost:8761/eureka/

UserController.java

@RestController
@RequestMapping("/users")
public class UserController {@GetMapping("/{id}")public User getUser(@PathVariable Long id) {return new User(id, "用户" + id, "user" + id + "@example.com");}
}// 实体类
public class User {private Long id;private String name;private String email;// 构造方法/getters/setters
}

3. Service Consumer (服务消费者)

application.yml

server:port: 8080
spring:application:name: order-service
eureka:client:service-url:defaultZone: http://localhost:8761/eureka/

Feign Client 接口

@FeignClient(name = "user-service")
public interface UserServiceClient {@GetMapping("/users/{id}")User getUserById(@PathVariable("id") Long userId);// 请求参数示例@GetMapping("/users/search")User searchUser(@RequestParam("name") String name);
}

OrderController.java

@RestController
@RequestMapping("/orders")
public class OrderController {@Autowiredprivate UserServiceClient userServiceClient;@GetMapping("/{orderId}/user")public User getOrderUser(@PathVariable Long orderId) {// 通过Feign调用用户服务Long userId = orderId * 10; // 模拟用户IDreturn userServiceClient.getUserById(userId);}
}

启用Feign (主类)

@SpringBootApplication
@EnableFeignClients
public class OrderServiceApplication {public static void main(String[] args) {SpringApplication.run(OrderServiceApplication.class, args);}
}

4. 高级配置

自定义Feign配置

@Configuration
public class FeignConfig {@BeanLogger.Level feignLoggerLevel() {return Logger.Level.FULL; // 详细日志}@Beanpublic RequestInterceptor authInterceptor() {return template -> template.header("Authorization", "Bearer token123");}
}

使用配置

@FeignClient(name = "user-service",configuration = FeignConfig.class,fallback = UserServiceFallback.class // 熔断回退
)
public interface UserServiceClient { ... }

熔断回退实现

@Component
public class UserServiceFallback implements UserServiceClient {@Overridepublic User getUserById(Long userId) {return new User(0L, "备用用户", "fallback@example.com");}
}

日志配置 (application.yml)

logging:level:org.springframework.cloud.openfeign: DEBUG

---

测试流程

1. 启动 Eureka Server (8761端口)
2. 启动 User Service (8081端口)
3. 启动 Order Service (8080端口)
4. 访问测试：http://localhost:8080/orders/123/user

关键概念总结

1. 服务注册：Provider 启动时向 Eureka 注册信息
2. 服务发现：Consumer 通过服务名发现 Provider
3. 负载均衡：Feign 自动实现多实例轮询
4. 声明式调用：定义接口即完成远程调用
5. 熔断机制：快速失败 + 服务降级

注：当前 Spring Cloud 版本默认使用 LoadBalancer 替代 Ribbon，最新版 OpenFeign 已内置负载均衡能力。

通过这个完整示例，可以清晰看到Eureka实现服务治理、Feign简化服务调用的协作过程，是构建微服务架构的基础设施。