通过 URLConnection 将音频文件从客户端传输到 Http 服务器

Question

i am currently working on a programming-project in my school. I need to send an audio file (MIDI format) from the Client successfully to a Http Server. I already tried to do this myself and did much research on the internet and in the Stackoverflow forum. Currently it is possible to send the file from the client to the server, but on the server side, the audio file is not playable.

The following is the client-side-code:

private static void sendPOST() throws IOException{
    final int mid = 1;
    final String POST_URL = "http://localhost:8080/musiker/hörprobe?mid="+mid;
    final File uploadFile = new File("C://Users//Felix Ulbrich//Desktop//EIS Prototype MIDIs//Pop//BabyOneMoreTime.mid");
    String boundary = Long.toHexString(System.currentTimeMillis()); 
    String CRLF = "\r\n";
    String charset = "UTF-8";
    URLConnection connection = new URL(POST_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, charset), true);
        ){
        writer.append("--" + boundary).append(CRLF);
        writer.append("Content-Disposition: form-data; name=\"binaryFile\"; filename=\"" + uploadFile.getName() + "\"").append(CRLF);
        writer.append("Content-Type: " + URLConnection.guessContentTypeFromName(uploadFile.getName())).append(CRLF);
        writer.append("Content-Transfer-Encoding: binary").append(CRLF);
        writer.append(CRLF).flush();
        Files.copy(uploadFile.toPath(), output);
        output.flush();
        writer.append(CRLF).flush();

        writer.append("--" + boundary + "--").append(CRLF).flush();

        int responseCode = ((HttpURLConnection) connection).getResponseCode();
        System.out.println(responseCode);
        }
}

The following is the server-side-code:

int FILE_SIZE = Integer.MAX_VALUE-2;
                    int bytesRead = 0;
                    int current = 0;
                    FileOutputStream fos = null;
                    BufferedOutputStream bos = null;
                    byte[] mybytearray = new byte[FILE_SIZE];
                    String FILE_TO_RECEIVED = "C://root//m"+musikerid+"hp"+(hörprobenzaehler+1)+".mid";
                    File f = new File(FILE_TO_RECEIVED);
                    if(!f.exists()){
                        f.createNewFile();
                    }
                    InputStream input = t.getRequestBody();
                    fos = new FileOutputStream(FILE_TO_RECEIVED);
                    bos = new BufferedOutputStream(fos);
                    bytesRead = input.read(mybytearray,0,mybytearray.length);
                    current = bytesRead;
                    do{
                        bytesRead = input.read(mybytearray, current, mybytearray.length-current);
                        if(bytesRead >= 0){
                            current += bytesRead;
                        }
                    }while(bytesRead>-1);

                    bos.write(mybytearray,0,current);
                    bos.flush();
                    fos.close();
                    bos.close();
                    t.sendResponseHeaders(200, 0);
                    input.close();

I am pretty desperate right now, because i couldn't find any solution to this problem. I need to use an HTTP server, but i don't need to use the TCP protocol (which is used right now via streams). I thought about a solution via ftp so i don't need to convert the file to a byte-array first. I assume that the problem lies exactly there. The server can't create the audio-file (midi-file) correctly from the byte-array. If anyone of you knows of a solution. Pls, i need your help :D

Greetings, Gizpo

Answer 1

So I've dug deeper into the matter. I've found several problems:

• You're mixing binary and character based I/O. While you get away with it on the client side, the server has a hard time dealing with this.
• You forgot to specify the size of the file you're sending over to the server. On the server side you have no way of knowing (unless some one tells you beforehand) what the size (of the incoming file) will be.

I've edited your code and came up with this:

---

Client:

private static void sendPOST() throws IOException{
        final int mid = 1;
        final String POST_URL = "http://localhost:8080/musiker/hörprobe?mid="+mid;
        final File uploadFile = new File("C://Users//Felix Ulbrich//Desktop//EIS Prototype MIDIs//Pop//BabyOneMoreTime.mid");

        String boundary = Long.toHexString(System.currentTimeMillis()); 
        String CRLF = "\r\n";
        String charset = "UTF-8";
        URLConnection connection = new URL(POST_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, charset), true);
        ) {
            writer.append("--" + boundary).append(CRLF);
            writer.append("Content-Disposition: form-data; name=\"binaryFile\"; filename=\"" + uploadFile.getName() + "\"").append(CRLF);
            writer.append("Content-Length: " + uploadFile.length()).append(CRLF);
            writer.append("Content-Type: " + URLConnection.guessContentTypeFromName(uploadFile.getName())).append(CRLF);
            writer.append("Content-Transfer-Encoding: binary").append(CRLF);
            writer.append(CRLF).flush();
            Files.copy(uploadFile.toPath(), output);
            output.flush();

            int responseCode = ((HttpURLConnection) connection).getResponseCode();
            System.out.println("Response code: [" + responseCode + "]");
        }
    }

Server:

@Override
public void handle(HttpExchange t) throws IOException {
    String CRLF = "\r\n";
    int fileSize = 0;
    
    String FILE_TO_RECEIVED = "C://root//m"+musikerid+"hp"+(hörprobenzaehler+1)+".mid";
    File f = new File(FILE_TO_RECEIVED);
    if (!f.exists()) {
        f.createNewFile();
    }
    
    InputStream input = t.getRequestBody();
    String nextLine = "";
    do {
        nextLine = readLine(input, CRLF);
        if (nextLine.startsWith("Content-Length:")) {
            fileSize = 
                Integer.parseInt(
                    nextLine.replaceAll(" ", "").substring(
                        "Content-Length:".length()
                    )
                );
        }
        System.out.println(nextLine);
    } while (!nextLine.equals(""));
    
    byte[] midFileByteArray = new byte[fileSize];
    int readOffset = 0;
    while (readOffset < fileSize) {
        int bytesRead = input.read(midFileByteArray, readOffset, fileSize);
        readOffset += bytesRead;
    }
    
    BufferedOutputStream bos = 
        new BufferedOutputStream(new FileOutputStream(FILE_TO_RECEIVED));
    
    bos.write(midFileByteArray, 0, fileSize);
    bos.flush();
    
    t.sendResponseHeaders(200, 0);
}

private static String readLine(InputStream is, String lineSeparator) 
    throws IOException {

    int off = 0, i = 0;
    byte[] separator = lineSeparator.getBytes("UTF-8");
    byte[] lineBytes = new byte[1024];
    
    while (is.available() > 0) {
        int nextByte = is.read();
        if (nextByte < -1) {
            throw new IOException(
                "Reached end of stream while reading the current line!");
        }
        
        lineBytes[i] = (byte) nextByte;
        if (lineBytes[i++] == separator[off++]) {
            if (off == separator.length) {
                return new String(
                    lineBytes, 0, i-separator.length, "UTF-8");
            }
        }
        else {
            off = 0;
        }
        
        if (i == lineBytes.length) {
            throw new IOException("Maximum line length exceeded: " + i);
        }
    }
    
    throw new IOException(
        "Reached end of stream while reading the current line!");       
}