java.io.FilePermission - access denied

Applets are by default denied from accessing the client's file I/O. You need to sign your applet or edit the policy files.

As far as i know Applets cannot write to files as this would be a security violation. You can expressly grant the file-writing permission to the JVM to enable this but i think that would be a really bad idea because your users would be allowing you to write whatever you wanted to their disk via the web. Why does your applet want to write to a file?

Is your applet signed? Non signed applets can't access files. See here: http://java.sun.com/developer/onlineTraining/Programming/JDCBook/signed.html

Do like this:

 fos=AccessController.doPrivileged(new PrivilegedAction()
    public  FileOutputStream run() {
      return new FileOutputStream(f1);
    }
  });

or edit file "java.policy" add permission java.io.FilePermission "<<ALL FILES>>", "read,write";