Feign是Netflix開發(fā)的聲明試、模版化的HTTP客戶端，它調(diào)用HTTP API更加便捷優(yōu)雅。

一、基礎(chǔ)應(yīng)用

1.feign使用

增加feign依賴

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

編寫feign接口

@FeignClient(name = "microservice-provider-user")
public interface UserFeignClient {
    @PostMapping("/api/user")
    String find();
}

@FeignClient注解的name 是指定FeignClient的名稱，如果項(xiàng)目使用了Ribbon\Consul等，name屬性會(huì)作為微服務(wù)的名稱，用于服務(wù)發(fā)現(xiàn)。還可以使用url可以手動(dòng)指定@FeignClient調(diào)用的地址。

啟用feign

啟動(dòng)類增加 @EnableFeignClients 注解

調(diào)試

    @PostMapping("/serviceInstance")
    public String serviceInstance() {
        return userFeignClient.find();
    }

結(jié)果：

[{"id":1,"username":"account1","name":"張三","age":20,"balance":150.00},
{"id":2,"username":"account2","name":"李四","age":25,"balance":350.00},
{"id":3,"username":"account3","name":"王五","age":28,"balance":450.00}]

2.feign自定義配置

SpringCloud中Feign默認(rèn)配置類是FeignClientsConfiguration，我們可以通過@FeignClient的configuration屬性自定義配置，自定義配置的優(yōu)先級會(huì)比FeignClientsConfiguration高。

創(chuàng)建Feign配置類

import feign.Contract;
import feign.Logger;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class FeignConfig {

    @Bean
    public Contract feignContract() {
        return new feign.Contract.Default();
    }

    @Bean
    public Logger.Level feignLoggerLevel() {
        return Logger.Level.FULL;
    }
}

以上包含兩項(xiàng)配置更改，使用Feign默認(rèn)契約和打印FULL級別的日志。

feign接口

@FeignClient(name = "microservice-provider-user", configuration = FeignConfig.class)
public interface UserFeignClient {

    @RequestLine("POST /api/user")
    String find();

}

注意使用feign自帶注解@RequestLine , 如果依然使用 @PostMapping會(huì)報(bào)如下錯(cuò)誤：

- Class UserFeignClient has annotations [FeignClient] that are not used by contract Default
- Method find has an annotation PostMapping that is not used by contract Default

原因是FeignClientsConfiguration類（如下代碼），F(xiàn)eign默認(rèn)使用的契約是SpringMvcContract，而通過自定義配置已經(jīng)更改成Feign契約，因此需要使用Feign的注解。

    @Bean
    @ConditionalOnMissingBean
    public Contract feignContract(ConversionService feignConversionService) {
        return new SpringMvcContract(this.parameterProcessors, feignConversionService);
    }

調(diào)試結(jié)果

部分日志如下，有feign FULL日志，結(jié)果正常返回

[UserFeignClient#find] ---> POST http://microservice-provider-user/api/user HTTP/1.1
[UserFeignClient#find] ---> END HTTP (0-byte body)
[UserFeignClient#find] <--- HTTP/1.1 200 (206ms)
[UserFeignClient#find] connection: keep-alive
[UserFeignClient#find] content-type: application/json
[UserFeignClient#find] date: Tue, 13 Oct 2020 03:32:43 GMT
[UserFeignClient#find] keep-alive: timeout=60
[UserFeignClient#find] transfer-encoding: chunked
[UserFeignClient#find] 
[UserFeignClient#find] [{"id":1,"username":"account1","name":"張三","age":20,"balance":150.00}]
[UserFeignClient#find] <--- END HTTP (220-byte body)

3.feign多參數(shù)請求

Get請求多參數(shù)URL，如下兩種寫法

    @GetMapping("/api/user")
    String find(@RequestParam("id") String id, @RequestParam("name") String name);

    @GetMapping("/api/user")
    String find(@RequestParam Map<String, Object> map);
    

Post請求包含多參數(shù)

    @PostMapping("/api/user")
    String find(@RequestBody User user);

github：https://github.com/OpenFeign/feign/#basics