How to get OutputStream/Writer for a file in a JSP code?

Question

In a JSP code as shown below, how could we get an OutputStream to write a file that resides on the server file system?
I'm stuck after five hours struggle!
<%
/* simple experimental JSP program */
...  // get request data
Properties pt = new Properties();
Class clas = getClass();
InputStream is = clas.getResourceAsStream("/users.properties");
pt.load(is);
String userNameDB = pt.getProperty("user");
String passwordDB = pt.getProperty("password");
long lastLogonDB = Long.parseLong(pt.getProperty("lastLogon"));
    // so far so good ...
if (userName.equals(userNameDB) && password.equals(passwordDB)){
  if (lastLogonForm > lastLogonDB) {
    session.setAttribute("User", userName); //Saves user name string in the session object
    pt.setProperty("lastLogon", lastLogon);
    pt.setProperty("user", userNameDB);
    pt.setProperty("password", passwordDB);
    ...  // how to write back the new data to the users.properties file?
%>

Answer 1

I have found a solution:
String path = application.getRealPath("/users.properties");
InputStream is = new FileInputStream(path);
is.close();
OutputStream os = new FileOutputStream(path);
os.close();getResourceAsStream() is oddly incompatible with the code using the getRealPath(). So don't use it.