OpenFeign

OpenFeign是一个声明式的http客户端

快速入门

①：引入依赖

  <!--openFeign--><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId></dependency><!--负载均衡器--><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-loadbalancer</artifactId></dependency>

②：通过@EnableFeignClients注解，启用OpenFeign功能

@EnableFeignClients
@SpringBootApplication
public class CartApplication{}

③：编写FeignClient

@FeignClient(value = "item-service")  //服务名称
public interface ItemClient {@GetMapping("/items")  //请求方式和请求路径List<ItemDTO> queryItemByIds(@RequestParam("ids") Collection<Long> ids);
}

④：使用FeignClient，实现远程调用

List<ItemDTO> items = itemClient.queryItemByIds(itemIds);

*原来的写法

List<ServiceInstance> instances = discoveryClient.getInstances("item-service");if(CollUtils.isEmpty(instances)){return;}//2.2 手写负载均衡，从服务列表中挑选一个实例ServiceInstance instance = instances.get(RandomUtil.randomInt(instances.size()));//2.3 利用RestTemplate发起http请求，得到http响应ResponseEntity<List<ItemDTO>> response = restTemplate.exchange(instance.getUri() + "/items?ids={ids}",HttpMethod.GET,null,new ParameterizedTypeReference<List<ItemDTO>>() {},Map.of("ids", CollUtils.join(itemIds, ",")));

连接池

Feign底层发起http请求，依赖于其它的框架。其底层支持的http客户端实现包括：

• HttpURLConnection：默认实现，不支持连接池

• Apache HttpClient ：支持连接池

• OKHttp：支持连接池

①：导入依赖

<!--OK http 的依赖 -->
<dependency><groupId>io.github.openfeign</groupId><artifactId>feign-okhttp</artifactId>
</dependency>

②：配置文件中开启Feign的连接池功能

feign:okhttp:enabled: true # 开启OKHttp功能