Feign

# 引入依赖

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

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# 启动类中添加注解

@EnableFeignClients
@SpringBootApplication
public class Application{
    ...
}

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# 编写Feign客户端

在order-service中新建接口；

基于SpringMVC的注解来声明远程调用的信息，比如：
- 服务名称：userservice
- 请求方式：GET
- 请求路径：/user/{id}
- 请求参数：Long id
- 返回值类型：User
```
@FeignClient("userservice")
public interface UserClient {
    @GetMapping("/user/{id}")
    User findById(@PathVariable("id") Long id);
}
```
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order-service中；

@Autowired
private UserClient userClient;

public Order queryOrderById(Long orderId){
    Order order = orderMapper.findById(orderId);
    User user = userClient.findById(order.getUserId());
    order.setUser(user);
    return order;
}

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# 将Feign接口抽取为一个模块

← Nacos Gateway→