Opening Output Stream to a file on the server from Applet

Question

Hi,
I am trying to write a little applet which parses a file found on the server , lets the user select some Strings then write the selected Strings to a different file on the server. I use the following code:
String fileName = new String("LineUp");
URL docBase = null;
URLConnection conn = null;
try {
docBase = new URL(ApppletName.codeBase, fileName);
} catch (java.net.MalformedURLException e) {
System.out.println("Couldn't create image: "
+ "badly specified URL");
try {
conn = docBase.openConnection();
} catch(IOException e) {System.out.println(e);}
String playerString;
try {
conn.setAllowUserInteraction(true);
conn.setDoOutput(true);
conn.connect();
PrintWriter out = new PrintWriter(
conn.getOutputStream());
etc..
The problem I am having is that the getOutputStream routine for the connection object does nothing other than throw an exception (I've stepped through the code and that is all the routine actually does). The connection is actually made but no output stream can be created. I have looked at the Java Tutorial (as I am fairly new to Java) and found a spot where they tell you how to write to a file on the server, which is the example I have followed. Any suggestions? What am I missing?

Answer 1

Yes, that's what I thought. It talks about writing to a URL, and you have interpreted "URL" as if it meant "file". A URL is a "Uniform Resource Locator", which is a string that identifies a "resource" on the server. Often that corresponds to a file on the server, but not always. It could be a page that is dynamically generated by a script on the server.
Look again at that page and you will see these words: "At the other end, a cgi-bin script (usually) on the server receives the data, processes it, and then sends you a response, usually in the form of a new HTML page." What that means is, you can't just upload a file to a URL unless you have programmed the server to deal with that upload. That's part of the basic design of the HTTP protocol.
So, unfortunately, you can't do what you want all that easily. You would have to provide some programming at the server to handle the file upload for you. In Java that means writing a servlet and getting the web server to have that servlet handle all requests to a particular URL. I suspect you don't want to get into that just yet. But if you do, any decent book on Java servlets should have an example of how to upload files like this.