feign multipart/form-data

To feign a multipart/form-data request, you can use the `@RequestPart` annotation in Feign.

Here's an example of how you can do it:

import feign.Headers;
import feign.Param;
import feign.RequestLine;
import feign.codec.Encoder;
import feign.form.spring.SpringFormEncoder;
import org.springframework.web.bind.annotation.RequestPart;
import org.springframework.web.multipart.MultipartFile;

public interface MyApiClient {
    
    @RequestLine("POST /upload")
    @Headers("Content-Type: multipart/form-data")
    void uploadFile(@Param("file") @RequestPart("file") MultipartFile file);
}

In this example, we define an interface `MyApiClient` with a single method `uploadFile` that takes a `MultipartFile` as a parameter. The `@RequestLine` annotation specifies the HTTP method and the endpoint path. The `@Headers` annotation sets the content type to `multipart/form-data`.

To use this Feign client, you need to configure the `Encoder` to use the `SpringFormEncoder`. Here's an example using Spring Boot:

import feign.codec.Encoder;
import feign.form.spring.SpringFormEncoder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class FeignConfig {
    
    @Bean
    public Encoder feignFormEncoder() {
        return new SpringFormEncoder();
    }
}

With this configuration, you can now use the `MyApiClient` interface to make requests, and Feign will handle the conversion of the `MultipartFile` to a multipart/form-data request.