Dynamic generation of jnlp file

Question

I'm dynamically generating a jnlp file using a jsp to pass run-time parameters over to my Java application thusly:
<%
response.setContentType("application/x-java-jnlp-file");
String userName = request.getParameter("username");
String password = request.getParameter("password");
String batchId = request.getParameter("batchid");
out.println("<?xml version=\"1.0\" encoding=\"utf-8\"?>");
out.println("<jnlp ");
out.println("spec=\"1.0+\" ");
out.println("codebase=\"http://server/directory\" ");
out.println("href=\"this jsp file\">");
... other jnlp stuff...
out.println("<application-desc main-class=\"myApp.myClass\">");
out.println("<argument>" + userName + "</argument>");
out.println("<argument>" + password + "</argument>");
out.println("<argument>" + batchId + "</argument>");
out.println("</application-desc>");
out.println("</jnlp>");
And use args[] to attempt to get the passed parameters in the Java application:
userName = args[0];
password = args[1];
batchId = args[2];
However, they don't seem to be passed over to the application as I get NullPointerExceptions. If I try to trace the state of the arguments by adding:
FileOutputStream f = new FileOutputStream("w:output.txt");
BufferedWriter w = new BufferedWriter(new OutputStreamWriter(f, System.getProperty("file.encoding")));
w.write("userName: " + userName);
w.write("password: " + password);
w.write("batchId: " + batchId);
f.flush();
f.close();
The output file is completely empty.
1. Am I passing the arguments in wrongly?
2. Why is the output not being written in the file?
My thanks in advance for any assistance offered.
Erkton

Answer 1

Erkton,
I use a similar approach and it does work. The main gotchas I found were typos. I would suggest temporarily changing the
response.setContentType("application/x-java-jnlp-file");
line to
response.setContentType("text/xml");
and looking at your JNLP file as XML and verifything that you got everything write. Look for beginning and end tags, stuff like that.
Once you have it right then switch it back to JNLP.
One other thing to look out for is Internet Explorer doesn't like jnlp files unless they end with a .jnlp extension. I had to rename my jnlp files to end with .jnlp instead of .jsp for IE to parse them correctly. I don't think thats the issue you are running into, but you may want to look out for it.