How to handle Server side HTTP file upload from Java client

Question

I want to upload a file from a client to a server.

Client: Java using HTTP post Server: Java Servlet

I have added the client side coding here. But, i don't have any idea with the server side processing. Please do help me with a code snippet.

 private String Tag = "UPLOADER";
    private String urlString = "http://192.168.42.140:8080/sampweb";
    HttpURLConnection conn;
    String exsistingFileName = "/sdcard/log.txt";
    String lineEnd = "\r\n";
    String twoHyphens = "--";
    String boundary = "*****";
    try {
        // ------------------ CLIENT REQUEST

        Log.e(Tag, "Inside second Method");

        FileInputStream fileInputStream = new FileInputStream(new File(
                exsistingFileName));

        // open a URL connection to the Servlet

        URL url = new URL(urlString);

        // Open a HTTP connection to the URL

        conn = (HttpURLConnection) url.openConnection();

        // Allow Inputs
        conn.setDoInput(true);

        // Allow Outputs
        conn.setDoOutput(true);

        // Don't use a cached copy.
        conn.setUseCaches(false);

        // Use a post method.
        conn.setRequestMethod("POST");

        conn.setRequestProperty("Connection", "Keep-Alive");

        conn.setRequestProperty("Content-Type",
                "multipart/form-data;boundary=" + boundary);

        DataOutputStream dos = new DataOutputStream(conn.getOutputStream());

        dos.writeBytes(twoHyphens + boundary + lineEnd);
        dos
                .writeBytes("Content-Disposition: post-data; name=uploadedfile;filename="
                        + exsistingFileName + "" + lineEnd);
        dos.writeBytes(lineEnd);

        Log.e(Tag, "Headers are written");

        // create a buffer of maximum size

        int bytesAvailable = fileInputStream.available();
        int maxBufferSize = 1000;
        // int bufferSize = Math.min(bytesAvailable, maxBufferSize);
        byte[] buffer = new byte[bytesAvailable];

        // read file and write it into form...

        int bytesRead = fileInputStream.read(buffer, 0, bytesAvailable);

        while (bytesRead > 0) {
            dos.write(buffer, 0, bytesAvailable);
            bytesAvailable = fileInputStream.available();
            bytesAvailable = Math.min(bytesAvailable, maxBufferSize);
            bytesRead = fileInputStream.read(buffer, 0, bytesAvailable);
        }

        // send multipart form data necessary after file data...

        dos.writeBytes(lineEnd);
        dos.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);

        // close streams
        Log.e(Tag, "File is written");
        fileInputStream.close();
        dos.flush();
        dos.close();

    } catch (MalformedURLException ex) {
        Log.e(Tag, "error: " + ex.getMessage(), ex);
    }

    catch (IOException ioe) {
        Log.e(Tag, "error: " + ioe.getMessage(), ioe);
    }

    try {
        BufferedReader rd = new BufferedReader(new InputStreamReader(conn
                .getInputStream()));
        String line;
        while ((line = rd.readLine()) != null) {
            Log.e("Dialoge Box", "Message: " + line);
        }
        rd.close();

    } catch (IOException ioex) {
        Log.e("MediaPlayer", "error: " + ioex.getMessage(), ioex);
    }
}

I'm new to the server programming. If i have done any mistakes do clarify me. Thanks!

Solution

The best library to achieve this is still the Apache Commons File Upload. It is well documented and easy to use. If you ran into any issues, please check FAQ first.