How can I make a multipart/form-data POST request using Java?

Here's a solution that does not require any libraries.

This routine transmits every file in the directory d:/data/mpf10 to urlToConnect

String boundary = Long.toHexString(System.currentTimeMillis());
URLConnection connection = new URL(urlToConnect).openConnection();
connection.setDoOutput(true);
connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
PrintWriter writer = null;
try {
    writer = new PrintWriter(new OutputStreamWriter(connection.getOutputStream(), "UTF-8"));
    File dir = new File("d:/data/mpf10");
    for (File file : dir.listFiles()) {
        if (file.isDirectory()) {
            continue;
        }
        writer.println("--" + boundary);
        writer.println("Content-Disposition: form-data; name=\"" + file.getName() + "\"; filename=\"" + file.getName() + "\"");
        writer.println("Content-Type: text/plain; charset=UTF-8");
        writer.println();
        BufferedReader reader = null;
        try {
            reader = new BufferedReader(new InputStreamReader(new FileInputStream(file), "UTF-8"));
            for (String line; (line = reader.readLine()) != null;) {
                writer.println(line);
            }
        } finally {
            if (reader != null) {
                reader.close();
            }
        }
    }
    writer.println("--" + boundary + "--");
} finally {
    if (writer != null) writer.close();
}
// Connection is lazily executed whenever you request any status.
int responseCode = ((HttpURLConnection) connection).getResponseCode();
// Handle response

httpcomponents-client-4.0.1 worked for me. However, I had to add the external jar apache-mime4j-0.6.jar (org.apache.james.mime4j) otherwise reqEntity.addPart("bin", bin); would not compile. Now it's working like charm.

I found this sample in Apache's Quickstart Guide. It's for version 4.5:

/**
 * Example how to use multipart/form encoded POST request.
 */
public class ClientMultipartFormPost {

    public static void main(String[] args) throws Exception {
        if (args.length != 1)  {
            System.out.println("File path not given");
            System.exit(1);
        }
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            HttpPost httppost = new HttpPost("http://localhost:8080" +
                    "/servlets-examples/servlet/RequestInfoExample");

            FileBody bin = new FileBody(new File(args[0]));
            StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN);

            HttpEntity reqEntity = MultipartEntityBuilder.create()
                    .addPart("bin", bin)
                    .addPart("comment", comment)
                    .build();


            httppost.setEntity(reqEntity);

            System.out.println("executing request " + httppost.getRequestLine());
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                System.out.println("----------------------------------------");
                System.out.println(response.getStatusLine());
                HttpEntity resEntity = response.getEntity();
                if (resEntity != null) {
                    System.out.println("Response content length: " + resEntity.getContentLength());
                }
                EntityUtils.consume(resEntity);
            } finally {
                response.close();
            }
        } finally {
            httpclient.close();
        }
    }
}

You will happy!

   <dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.13</version>
   </dependency>
   <dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpmime</artifactId>
    <version>4.3.1</version>
   </dependency>

import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.entity.mime.content.ByteArrayBody;


byte[] byteArr1 = multipartFile1.getBytes();
byte[] byteArr2 = multipartFile2.getBytes();

HttpEntity reqEntity = MultipartEntityBuilder.create().setCharset(Charset.forName("UTF-8"))
                .addPart("image1", new ByteArrayBody(byteArr1, req.getMultipartFile1().getOriginalFilename()))
                .addPart("image2", new ByteArrayBody(byteArr2, req.getMultipartFile2().getOriginalFilename()))
                .build();

My code post multipartFile to server.

  public static HttpResponse doPost(
    String host,
    String path,
    String method,
    MultipartFile multipartFile
  ) throws IOException
  {

    HttpClient httpClient = wrapClient(host);
    HttpPost httpPost = new HttpPost(buildUrl(host, path));

    if (multipartFile != null) {

      HttpEntity httpEntity;

      ContentBody contentBody;
      contentBody = new ByteArrayBody(multipartFile.getBytes(), multipartFile.getOriginalFilename());
      httpEntity = MultipartEntityBuilder.create()
                                         .addPart("nameOfMultipartFile", contentBody)
                                         .build();

      httpPost.setEntity(httpEntity);

    }
    return httpClient.execute(httpPost);
  }

My code for sending files to server using post in multipart. Make use of multivalue map while making request for sending form data

  LinkedMultiValueMap<String, Object> map = new LinkedMultiValueMap<>();
        map.add("FILE", new FileSystemResource(file));
        map.add("APPLICATION_ID", Number);

   httpService.post( map,headers);

At receiver end use

@RequestMapping(value = "fileUpload", method = RequestMethod.POST)
    public ApiResponse AreaCsv(@RequestParam("FILE") MultipartFile file,@RequestHeader("clientId") ){
//code
}

Using HttpRequestFactory to jira xray's /rest/raven/1.0/import/execution/cucumber/multipart :

Map<String, Object> params = new HashMap<>();
            params.put( "info", "zigouzi" );
            params.put(  "result", "baalo"  );
            HttpContent content = new UrlEncodedContent(params);

            OAuthParameters oAuthParameters = jiraOAuthFactory.getParametersForRequest(ACCESS_TOKEN, CONSUMER_KEY, PRIVATE_KEY);
            HttpRequestFactory requestFactory = new NetHttpTransport().createRequestFactory(oAuthParameters);
            HttpRequest request = requestFactory.buildPostRequest(new GenericUrl(url),   content);
            request.getHeaders().setAccept("application/json");
            String boundary = Long.toHexString(System.currentTimeMillis());
            request.getHeaders().setContentType("multipart/form-data; boundary="+boundary);
            request.getHeaders().setContentEncoding("application/json");
            HttpResponse response = null ;
            try
            {
                response = request.execute();
                Scanner s = new Scanner(response.getContent()).useDelimiter("\\A");
                result = s.hasNext() ? s.next() : "";
            }
            catch (Exception e)
            {
                 
            }

did the trick.