Comment télécharger des fichiers avec des paramètres supplémentaires à l'aide de java.net.URLConnection et de l'encodage multipart/form-data ?

<code class="java">import java.io.File;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.URLConnection;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;

public class FileUpload {

    public static void main(String[] args) throws Exception {
        String url = "http://example.com/upload";
        String param = "value";
        File textFile = new File("/path/to/file.txt");
        File binaryFile = new File("/path/to/file.bin");
        String boundary = Long.toHexString(System.currentTimeMillis());

        URLConnection connection = new URL(url).openConnection();
        connection.setDoOutput(true);
        connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

        try (OutputStream output = connection.getOutputStream();
             PrintWriter writer = new PrintWriter(new OutputStreamWriter(output, StandardCharsets.UTF_8), true)) {
            // Send parameter
            writer.append("--" + boundary).append("\r\n");
            writer.append("Content-Disposition: form-data; name=\"param\"").append("\r\n");
            writer.append("Content-Type: text/plain; charset=" + StandardCharsets.UTF_8).append("\r\n");
            writer.append("\r\n").append(param).append("\r\n").flush();

            // Send text file
            writer.append("--" + boundary).append("\r\n");
            writer.append("Content-Disposition: form-data; name=\"textFile\"; filename=\"" + textFile.getName() + "\"").append("\r\n");
            writer.append("Content-Type: text/plain; charset=" + StandardCharsets.UTF_8).append("\r\n");
            writer.append("\r\n").flush();
            Files.copy(textFile.toPath(), output);
            output.flush();
            writer.append("\r\n").flush();

            // Send binary file
            writer.append("--" + boundary).append("\r\n");
            writer.append("Content-Disposition: form-data; name=\"binaryFile\"; filename=\"" + binaryFile.getName() + "\"").append("\r\n");
            writer.append("Content-Type: " + URLConnection.guessContentTypeFromName(binaryFile.getName())).append("\r\n");
            writer.append("Content-Transfer-Encoding: binary").append("\r\n");
            writer.append("\r\n").flush();
            Files.copy(binaryFile.toPath(), output);
            output.flush();
            writer.append("\r\n").flush();

            // End of multipart/form-data
            writer.append("--" + boundary + "--").append("\r\n").flush();
        }

        int responseCode = ((HttpURLConnection) connection).getResponseCode();
        System.out.println("Response Code: " + responseCode);
    }
}</code>