Feign是Netflix开发的声明试、模版化的HTTP客户端，它调用HTTP API更加便捷优雅。
一、基础应用
1.feign使用
增加feign依赖
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
编写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的名称，如果项目使用了Ribbon\Consul等，name属性会作为微服务的名称，用于服务发现。还可以使用url可以手动指定@FeignClient调用的地址。
启用feign
启动类增加 @EnableFeignClients 注解
调试
@PostMapping("/serviceInstance")
public String serviceInstance() {
return userFeignClient.find();
}
结果：
[{"id":1,"username":"account1","name":"张三","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自定义配置
SpringCloud中Feign默认配置类是FeignClientsConfiguration，我们可以通过@FeignClient的configuration属性自定义配置，自定义配置的优先级会比FeignClientsConfiguration高。
创建Feign配置类
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;
}
}
以上包含两项配置更改，使用Feign默认契约和打印FULL级别的日志。
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自带注解@RequestLine , 如果依然使用 @PostMapping会报如下错误：
- 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类（如下代码），Feign默认使用的契约是SpringMvcContract，而通过自定义配置已经更改成Feign契约，因此需要使用Feign的注解。
@Bean
@ConditionalOnMissingBean
public Contract feignContract(ConversionService feignConversionService) {
return new SpringMvcContract(this.parameterProcessors, feignConversionService);
}
调试结果
部分日志如下，有feign FULL日志，结果正常返回
[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":"张三","age":20,"balance":150.00}]
[UserFeignClient#find] <--- END HTTP (220-byte body)
3.feign多参数请求
Get请求多参数URL，如下两种写法
@GetMapping("/api/user")
String find(@RequestParam("id") String id, @RequestParam("name") String name);
@GetMapping("/api/user")
String find(@RequestParam Map<String, Object> map);
Post请求包含多参数
@PostMapping("/api/user")
String find(@RequestBody User user);
