Today I was trying to create an application that reads data from a website. The problem I had was that the form I needed to fill in to get to the page I want to read is a page with a POST form.
Due to the fact it was a POST form I could not create a simple URLConnection with a url and the querystring parameters that were needed.

To solve this problem you need to create a URLConnection and write the additional POST parameters to the connection.

First of all the basic code of how to create a URLConnection and read the file line by line.

try {
    // Send data
    URL url = new URL("http://cedricascoop.be/Search.aspx?__ufps=066834&l=NL&s=1&p=1");
    URLConnection conn = url.openConnection();

    // Get the response
    BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));
    String line;
    while ((line = rd.readLine()) != null) {
        // Process line...
        System.out.println(line);
    }
    rd.close();
} catch (Exception e) {
}

Now if we want to write some parameters we need to create a OutputStreamWriter. Here we can pass on all the post parameters needed. The parameters need to be UTF-8 encoded.
Following some code to create a URLConnection, pass on some parameters and read it out.

try {
    // Construct data
    String data = URLEncoder.encode("trainNumberTextBox", "UTF-8") + "=" + URLEncoder.encode("4518", "UTF-8");
    data += "&" + URLEncoder.encode("__EVENTTARGET", "UTF-8") + "=" + URLEncoder.encode("searchDepartureCommand", "UTF-8");
    data += "&" + URLEncoder.encode("__EVENTARGUMENT", "UTF-8") + "=" + URLEncoder.encode("searchForm", "UTF-8");
    data += "&" + URLEncoder.encode("__ET", "UTF-8") + "=" + URLEncoder.encode("", "UTF-8");            

    // Send data
    URL url = new URL("http://cedricascoop.bnet.be/Search.aspx?__ufps=066834&l=NL&s=1&p=1");
    URLConnection conn = url.openConnection();
    conn.setDoOutput(true);
    OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());
    wr.write(data);
    wr.flush();

    // Get the response
    BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));
    String line;
    while ((line = rd.readLine()) != null) {
        // Process line...
        System.out.println(line);
    }
    wr.close();
    rd.close();
} catch (Exception e) {
}