[cloud native] introduction and use of feign of microservices

Preface ：
Recently, I am learning about micro Services , Read the relevant courses of dark horse , Will relate Feign The knowledge of has summed up some , I hope I can help you guys and deepen your impression
If there is anything to be improved in the article, please give me more advice
Xiao Wei first thanked everyone for their support

The following text begins

@[toc]

Feign An introduction to the

Feign Is a declarative artifact RPC Of REST client , It uses interface based annotation , Very convenient client configuration ,Spring Cloud to Feign Added support Spring MVC annotation , And integrate Ribbon And Eureka Support load balancing .

Feign yes ⼀ individual HTTP Lightweight client framework for requests . By connecting to ⼝ Oral and annotated ⽅ Style initiation HTTP Ask for a tune ⽤, Interface oriented programming , It's not like Java Through encapsulation HTTP Ask for the newspaper ⽂ Of ⽅ Direct adjustment ⽤.
Service consumption ⽅ Get the service ⽅ Of ⼝, And then it's like ⽤ Local connection ⼝⽅ Law ⼀ I'm going to adjust it ⽤, It's actually a remote request . Let's make it more convenient and elegant ⽤ be based on HTTP Of API, By ⼴ Pan Ying ⽤ stay Spring Cloud The solution of the ⽅ In the case .

Feign The advantages of

Before we used RestTemplate The code that initiates the remote call ：

String url = "http://userservice/user/" + order.getUserld();User user = restTemplate.getForObject(url, User.class);

The problems above are code ：
Poor readability , Inconsistent programming experience ;
Complex parameters URL Difficult to maintain
Feign It's a declarative one http client , Official address ：Feign The official link

Its function is to help us achieve http Send request , Solve the problems mentioned above .

Feign How to use

Take our previous project as an example
stay order-service Service pom Introduce in the file feign rely on ：

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

stay order-service Add comments to the startup class to open Feign The function of ：

@EnableFeignClients@MapperScan("cn.itcast.order,mapper")@SpringBootApplicationpublic class OrderApplicationpublic static void main(String[] args) [SpringApplication.run(OrderApplication.class,args)

stay order-service Create a new interface in , The contents are as follows ：

package cn.itcast.order.client;​import cn.itcast.order.pojo.User;import org.springframework.cloud.openfeign.FeignClient;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.PathVariable;​@FeignClient("userservice")public interface UserClient {     @GetMapping("/user/{id}")     User findById(@PathVariable("id") Long id); }

This client is mainly based on SpringMVC To declare the information of the remote call , such as ：

• The service name ：userservice
• Request mode ：GET
• Request path ：/user/{id}
• Request parameters ：Long id
• return type ：User

such ,Feign Can help us send http request , No need to use RestTemplate To send .

We modify order-service Medium OrderService Class queryOrderById Method , Use Feign Client instead of RestTemplate：

@Autowiredprivate UserClient userClient;public Order query0rderById(Long orderId) //1. Query order Order order = orderMapper.findById(orderId);//2.  utilize Feign launch http request   Query the user Useruser = userClient.findById(order.getUserId());//3. encapsulation user To 0rderorder.setUser(user);// 4. return return order;

Feign Summary of the use of

Use Feign Steps for ：

The first ① Step Introduce dependencies

The first ② Step add to @EnableFeignClients annotation

The first ③ Step To write FeignClient Interface

The first ④ Step Use FeignClient The method defined in replaces RestTemplate