[JAVA] How to achieve file upload with Feign

1.First of all

Last time explained how to realize file download with Feign. This time I would like to explain how to realize file upload with Feign. I implemented my own Decoder in the download, but I will use this because there is a dedicated module called feign-form for uploading. .. In addition, Official page of GitHub explains as follows.

This module adds support for encoding application/x-www-form-urlencoded and multipart/form-data forms.

2. Preparation of library

feign-form is a separate module, so add it to the dependency. Please refer to Another article for the basic pom.xml when using Feign.

pom.xml

    <!-- add feign-form for multipart : start -->
    <dependency>
        <groupId>io.github.openfeign.form</groupId>
        <artifactId>feign-form</artifactId>
        <version>3.3.0</version>
    </dependency>
    <!-- add feign-form for multipart : end -->

3. API interface definition

Defines the API interface. There are the following three types of argument data types that can be used for file upload data conversion (serialization).

• java.io.File: Set the upload file as File
• byte []: Set the file data of the upload file as byte []
• feign.form.FormData: Set the upload file with a dedicated class

As a sample, I would like to use three types of data this time.

UploadApi.java

package com.example.feign.demo.upload;

import java.io.File;

import feign.Headers;
import feign.Param;
import feign.RequestLine;
import feign.form.FormData;

public interface UploadApi {

    @RequestLine("POST /data/upload")
    @Headers("Content-Type: multipart/form-data")
    String upload(@Param("remarks") String remarks, @Param("uploadFile") File uploadFile);

    @RequestLine("POST /data/upload")
    @Headers("Content-Type: multipart/form-data")
    String upload(@Param("remarks") String remarks, @Param("uploadFile") byte[] uploadFile);

    @RequestLine("POST /data/upload")
    @Headers("Content-Type: multipart/form-data")
    String upload(@Param("remarks") String remarks, @Param("uploadFile") FormData uploadFile);
}

** Please note that all three types do not work the same. Check the specifications on the API provider (server) side and use the appropriate one. ** **

4. How to use

The point is to set an instance of the feign.form.FormEncoder class in the ʻencodermethod. Others are the same as the basic usage ofFeign`.

DownloadDemo.java

package com.example.feign.demo.upload;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

import feign.Feign;
import feign.Logger;
import feign.form.FormData;
import feign.form.FormEncoder;
import feign.jackson.JacksonEncoder;
import feign.okhttp.OkHttpClient;
import feign.slf4j.Slf4jLogger;

public class UploadDemo {

    public static void main(String[] args) {
        // 1. create instance of api interface with feign
        UploadApi uploadApi = Feign.builder()
                .client(new OkHttpClient())
                // use FormEncoder with JacksonEncoder
                .encoder(new FormEncoder(new JacksonEncoder()))
                // .encoder(new FormEncoder())
                .logger(new Slf4jLogger())
                .logLevel(Logger.Level.FULL)
                .target(UploadApi.class, "http://localhost:3000");

        // 2. call api
        // File
        File uploadFile = new File("C:/tmp/test.png ");
        String remarks = "I send a image file.";
        String result = uploadApi.upload(remarks, uploadFile);
        System.out.println(result);

        try (FileInputStream iStream = new FileInputStream(uploadFile);) {
            // byte[]
            byte[] uploadFileByte = new byte[(int) uploadFile.length()];
            iStream.read(uploadFileByte);
            String result2 = uploadApi.upload(remarks, uploadFileByte);
            System.out.println(result2);
            // FormData
            FormData formData = new FormData("image/png", uploadFileByte);
            String result3 = uploadApi.upload(remarks, formData);
            System.out.println(result3);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

5. Explain the difference between the three types with the implementation code (bonus)

The implementation code of feign-form is open to the public, so you can see the difference between the three types of operations. FormData can be solved by having a field of filename, but it is a mystery why it is not retained. (Although it retains contentType)

5.1. File

https://github.com/OpenFeign/feign-form/blob/master/feign-form/src/main/java/feign/form/multipart/SingleFileWriter.java

SingleFileWriter.Where the writeFileMetadata method of the parent class (AbstractWriter) is called in java

writeFileMetadata(output, key, file.getName(), null);

https://github.com/OpenFeign/feign-form/blob/master/feign-form/src/main/java/feign/form/multipart/AbstractWriter.java

AbstractWriter.java writeFileMetadata method

  @SneakyThrows
  protected void writeFileMetadata (Output output, String name, String fileName, String contentType) {
    val contentDesposition = new StringBuilder()
        .append("Content-Disposition: form-data; name=\"").append(name).append("\"; ")
        .append("filename=\"").append(fileName).append("\"")
        .toString();

    String fileContentType = contentType;
    if (fileContentType == null) {
      if (fileName != null) {
        fileContentType = URLConnection.guessContentTypeFromName(fileName);
      }
      if (fileContentType == null) {
        fileContentType = "application/octet-stream";
      }
    }

    val string = new StringBuilder()
        .append(contentDesposition).append(CRLF)
        .append("Content-Type: ").append(fileContentType).append(CRLF)
        .append("Content-Transfer-Encoding: binary").append(CRLF)
        .append(CRLF)
        .toString();

    output.write(string);
  }

In other words, in the case of File, it will be as follows.

• File.getName () is set to filename in Content-Disposition:
• Content-Type: is set to ʻURLConnection.guessContentTypeFromName (fileName)`

5.2. byte[]

https://github.com/OpenFeign/feign-form/blob/master/feign-form/src/main/java/feign/form/multipart/ByteArrayWriter.java

ByteArrayWriter.Where the writeFileMetadata method of the parent class (AbstractWriter) is called in java

writeFileMetadata(output, key, null, null);

In other words, in the case of byte [], it will be as follows.

• Content-Disposition: filename is set to null
• Content-Type: is set to ʻapplication / octet-stream`

5.3. FormData

https://github.com/OpenFeign/feign-form/blob/master/feign-form/src/main/java/feign/form/multipart/FormDataWriter.java

FormDataWriter.Where the writeFileMetadata method of the parent class (AbstractWriter) is called in java

writeFileMetadata(output, key, null, formData.getContentType());

In other words, in the case of FormData, it will be as follows.

• Content-Disposition: filename is set to null
• Content-Type: is set to formData.getContentType ()

6. Finally

This time, I explained how to realize file upload with Feign. I think it was easier than downloading because of the modules provided.