Spring Cloud

Spring Cloud 是微服务架构的一站式解决方案，提供分布式系统所需的组件。

核心组件

组件	说明	替代方案
Eureka	服务注册与发现	Nacos、Zookeeper
Gateway	API 网关	Spring Cloud Gateway
OpenFeign	服务调用	Dubbo
Ribbon	负载均衡	LoadBalancer
Hystrix	熔断器	Sentinel
Config	配置中心	Nacos Config
Sleuth	链路追踪	SkyWalking、Zipkin

快速开始

项目结构

├── cloud-eureka-server      # 注册中心
├── cloud-gateway            # 网关
├── cloud-user-service       # 用户服务
├── cloud-order-service      # 订单服务
└── cloud-common             # 公共模块

注册中心 Eureka

<!-- pom.xml -->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency>

# application.yml
server:
  port: 8761

eureka:
  instance:
    hostname: localhost
  client:
    register-with-eureka: false
    fetch-registry: false
    service-url:
      defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

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

服务提供者

spring:
  application:
    name: user-service

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/
  instance:
    prefer-ip-address: true

@RestController
@RequestMapping("/users")
public class UserController {
    @GetMapping("/{id}")
    public User getUser(@PathVariable Long id) {
        return new User(id, "User-" + id, 25);
    }
}

服务消费者 OpenFeign

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

@EnableFeignClients

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

@FeignClient(name = "user-service", fallback = UserFallback.class)
public interface UserClient {
    @GetMapping("/users/{id}")
    User getUser(@PathVariable("id") Long id);
}

// 降级处理
@Component
public class UserFallback implements UserClient {
    @Override
    public User getUser(Long id) {
        return new User(id, "默认用户", 0);
    }
}

@RestController
@RequestMapping("/orders")
public class OrderController {
    @Autowired
    private UserClient userClient;

    @GetMapping("/{userId}")
    public Order getOrder(@PathVariable Long userId) {
        User user = userClient.getUser(userId);
        return new Order(1L, userId, user.getName());
    }
}

API 网关 Gateway

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

spring:
  cloud:
    gateway:
      routes:
        - id: user-service
          uri: lb://user-service
          predicates:
            - Path=/api/users/**
          filters:
            - StripPrefix=1

        - id: order-service
          uri: lb://order-service
          predicates:
            - Path=/api/orders/**
          filters:
            - StripPrefix=1

负载均衡

Ribbon

user-service:
  ribbon:
    NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RoundRobinRule

LoadBalancer

@Configuration
public class LoadBalancerConfig {
    @Bean
    public ReactorLoadBalancer<ServiceInstance> random() {
        return new RandomLoadBalancer(
            new DefaultServiceInstanceListTransformer(),
            ServiceInstance.class.getClassLoader()
        );
    }
}

@Service
public class UserService {
    @Autowired
    private LoadBalancerClient loadBalancer;

    public String getServiceUrl() {
        ServiceInstance instance = loadBalancer.choose("user-service");
        return instance.getUri().toString();
    }
}

熔断器 Hystrix

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

@RestController
@RequestMapping("/orders")
@DefaultProperties(defaultFallback = "defaultFallback")
public class OrderController {

    @HystrixCommand(fallbackMethod = "getUserFallback",
                     commandProperties = {
        @HystrixProperty(name = "circuitBreaker.requestVolumeThreshold", value = "10"),
        @HystrixProperty(name = "circuitBreaker.sleepWindowInMilliseconds", value = "10000"),
        @HystrixProperty(name = "circuitBreaker.errorThresholdPercentage", value = "50")
    })
    @GetMapping("/{userId}")
    public String getOrder(@PathVariable Long userId) {
        return orderService.getOrder(userId);
    }

    public String getUserFallback(Long userId) {
        return "服务暂不可用，请稍后重试";
    }

    public String defaultFallback() {
        return "系统繁忙";
    }
}

总结

1. 注册中心：Eureka/Nacos 服务注册与发现
2. 服务调用：OpenFeign 声明式 HTTP 客户端
3. 网关：Gateway 统一入口、路由、过滤
4. 负载均衡：Ribbon/LoadBalancer
5. 熔断降级：Hystrix/Sentinel