How to send a video file from Java server socket to browser for downloading?

Question

I am trying to implement a server using Java. When I try to send a file, such as video or pdf, the connection is always reset. I am currently using OpenJDK 11 and Ubuntu.

void binaryResponse(OutputStream clientOutput, File file) throws IOException {

    int size= (int) file.length();
    String responseStr="HTTP/1.1 200 OK\r\n";
    responseStr+="Content-Type: application/force-download\r\n";
    responseStr+="Content-Length: " + size + "\r\n\r\n";

    clientOutput.write(responseStr.getBytes());

    FileInputStream fis = new FileInputStream(file);
    int bytes;
    byte[] buffer = new byte[4*1024];
    while (size > 0 && (bytes = fis.read(buffer, 0, Math.min(buffer.length, size))) != -1){
        clientOutput.write(buffer, 0, bytes);
        size -= bytes;
    }

    clientOutput.flush();
    fis.close();
}

Answer 1

application/force-download is not a valid media type (see Utility of HTTP header "Content-Type: application/force-download" for mobile? ).

You could use application/octet-stream instead, but a better option is to send the correct media type for the file type, ie application/pdf for a PDF file, etc (see How to get a file's Media Type (MIME type)? ), and then send a separate Content-Disposition: attachment header to trigger a download.

Also, when creating the Content-Length header, it is more efficient to use String.valueOf() or String.format() to convert the size integer to a String , rather than letting the operator+ do the conversion implicitly (see Concatenate integers to a String in Java for why).

Try this:

void binaryResponse(OutputStream clientOutput, File file) throws IOException {
    int size = (int) file.length();
    String responseStr = "HTTP/1.1 200 OK\r\n";
    responseStr += "Content-Type: application/octet-stream\r\n";
    responseStr += "Content-Length: " + String.valueOf(size) + "\r\n";
    responseStr += "Content-Disposition: attachment; filename=\"" + file.getName() + "\"\r\n\r\n";

    clientOutput.write(responseStr.getBytes());

    FileInputStream fis = new FileInputStream(file);
    int bytes;
    byte[] buffer = new byte[4*1024];
    while (size > 0 && (bytes = fis.read(buffer, 0, Math.min(buffer.length, size))) != -1){
        clientOutput.write(buffer, 0, bytes);
        size -= bytes;
    }

    clientOutput.flush();
    fis.close();
}