Open the connection:

URI url = new URL("http://localhost:8080/webservice/event.service");
// Opens a connection

URLConnection uconnection = url.openConnection();

// Set the properties
HttpURLConnection connection = (HttpURLConnection)uconnection;
connection.setDoOutput(true);
connection.setRequestMethod("POST");
connection.setRequestProperty("Content-Type",contentType);
connection.setRequestProperty("Content-Encoding","UTF-8");

// Setup the output for serialization
OutputStream os = connection.getOutputStream();
OutputStreamWriter o = new OutputStreamWriter(os,"UTF-8");

Now you write your XML to the writer.