Отправка пост запроса с файлом

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
 
public class TrayWindow {
    public static void main(String[] arg) throws MalformedURLException, IOException {
        String urlToConnect = "http://***********/uploadmulti";
        File fileToUpload = new File("C:/1.png");
        String boundary = Long.toHexString(System.currentTimeMillis()); // Just generate some unique random value.
 
        URLConnection connection = new URL(urlToConnect).openConnection();
        connection.setDoOutput(true); // This sets request method to POST.
        connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
        PrintWriter writer = null;
        try {
            writer = new PrintWriter(new OutputStreamWriter(connection.getOutputStream()));
            writer.println("--" + boundary);
            writer.println("Content-Disposition: form-data; file[]=\"picture\"; filename=\"1.png\"");
            writer.println("Content-Type: image/png");
            writer.println();
            BufferedReader reader = null;
            try {
                reader = new BufferedReader(new InputStreamReader(new FileInputStream(fileToUpload)));
                for (String line; (line = reader.readLine()) != null;) {
                    writer.println(line);
                }
            } finally {
                if (reader != null) try { reader.close(); } catch (IOException logOrIgnore) {}
            }
            writer.println("--" + boundary + "--");
        } finally {
            if (writer != null) writer.close();
        }
 
        // Connection is lazily executed whenever you request any status.
        int responseCode = ((HttpURLConnection) connection).getResponseCode();
        System.out.println(responseCode); // Should be 200
        
        InputStreamReader is = new InputStreamReader(connection.getInputStream(), "UTF-8");
        StringBuilder sb = new StringBuilder("");
        int bit;
        while ((bit = is.read()) != -1) sb.append((char)bit);
        is.close();
        
        System.out.println(sb);
        
    }
}