CODEWITHSUNDEEP
jakarta-eeservletsstreaming
Sebastian S.
Sebastian S.

Reputation: 1609

How to continuously stream text data to a servlet?

I have an Android app which connects to a server and continuously sends some signal data (using HttpURLConnection). On the server a script (shell or python, don't exactly know, it's not my part) currently processes this stream and for every incomming data package sets up a curl request to post this package to a servlet (running in a Jetty 8 web container). This is only a provisionary solution, since I don't know how to directly connect and stream the data to the servlet. As a requirement, the data transfer should use the HTTP protocol in order to be not blocked by any firewall.

So, is it possible to initially connect to a servlet and then stream data over a long time, say minutes or hours? I was wondering that I did not find similar questions/solutions. I mean this is not a special scenario. And is this the same operation as uploading a large file to a servlet?

The servlet actually looks like this:

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
    System.out.println("StreamingServlet#doPost(): IN");
    BufferedReader reader = request.getReader();
    String data = "";

    while ((data = reader.readLine()) != null)
    {
        System.out.println("Data: " + data);
    }
    reader.close();

    System.out.println("StreamingServlet#doPost(): OUT");
}

The android app has 3 methods using the HttpURLConnection:

private Boolean connect(URL URLdest)
{
    try
    {
        connection = (HttpURLConnection) URLdest.openConnection();
        connection.setDoOutput(true);
        connection.setChunkedStreamingMode(0);
        oSWout = new OutputStreamWriter(connection.getOutputStream());
    }
    catch (IOException e)
    {
        return false;
    }
    return true;
}   

public void send(String packet)
{
    try
    {
        // TODO clOSWout.write and clOSWout.flush block may freeze if connection is lost. Somehow no exception is thrown and thread hangs instead.
        // It only occurs if the Server breaks the connection

        oSWout.write(packet);
        oSWout.flush();
    }
    catch (IOException e)
    {
        ...
    }
}

public void stopConnection()
{
    try
    {
        oSWout.close();
        connection.disconnect();
    }
    catch (IOException e)
    {
        ...
    }
}

What I expect in the end is that when connecting to the servlet, it prints "StreamingServlet#doPost(): IN", then, for each incomming data package it should print the data string and when closing the connection it should print "StreamingServlet#doPost(): OUT" and finally return from the method.

But I guess I miss something and this is done in another way in Java EE. I don't know.

Upvotes: 3

Views: 2315

Answers (1)

Sebastian S.
Sebastian S.

Reputation: 1609

Finally, I solved the problem by myself:

Using the BufferedReader, all the data packages are collected (buffered) and are read and printed as one packege when the connection is closed. So I had to use the ServletInputStream [obtained by HttpServletRequest#getInputStream()] and read the data packages into a byte array using the read() method. Now everything works as I expected.

But I still wonder, if it is a more or less typical scenario to use a blocking operation and thus remain a long time (say minutes or hours) in the doPost() method or if the server is somehow expected to respond in much shorter time.

Upvotes: 2

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