Files and environment...

Question

Dear Java Experts,
There appears to be no limit to my confusion about some things with Java. The thing is
that the documentation is so very, very large I simply get lost :-( Here are a few questions
maybe you can help me with.
1) Assume I create a JAR that in it has a few resources, like for example a couple of JPG
images. Is it possible to copy such a resource to the file system and if yes, how is this
best done?
2) Talking about files, the File class has some nifty methods. There is a nice method for
creating directories, another for checking accessrights, another to check latest change, but
on the subject of copying, how is one supposed to copy one file from a give directory to
another in Java?
3) The last question...from what I read, the System class used to have a getenv method
which now has been depracted. Is it possible from a Java application to read an arbitrary
environment variable, let's call it FOO at any point? What is the proposed way of doing this?
I do apologize for my silly questions, but I have tried to read about this and I just drown in
information. At the end of the day sometimes it's better just to ask.
Greatful for any help you might be able to provide me with!
Best regards,
X.

Answer 1

Hi X,
(1) Do mean copying the JAR or the JPG files? If it's the JAR, you can copy that to any directory you wish. If you want to get at the JPG files, you'll have to open the JAR with something like *nix tar or Windows WinZip and extract the .jpg files from the JAR into a directory of your choice. 
A JAR, after all, is just a ZIP file with a manifest.
(2) There's no copy method in java.io.File, as you've noticed. You have to do it the hard way: open and read the source file, create the destination file, and write the contents of the source file into the destination.
Here's a snippet that does it using classes from the java.nio.channels package:
            RandomAccessFile raf    = new RandomAccessFile(source, "rw");
            FileChannel from        = raf.getChannel();
            File duplicate = null;
            // If the destination file is a directory, keep the source name
            // Otherwise, just copy to the given file name
            if (destination.isDirectory())
                duplicate = new File(destination, source.getName());
            else
                duplicate = destination;
            FileOutputStream fos    = new FileOutputStream(duplicate);
            FileChannel to          = fos.getChannel();
            // Obtain exclusive lock on file (the meaning of this is platform dependent)
            FileLock fileLock       = from.lock();
            // Transfer the contents
            long bytesTransferred   = from.transferTo(0, from.size(), to);
            // Drop the lock
            fileLock.release();
            // Close the channels and streams
            to.close();
            from.close();(3) Here's how:
String env = System.getProperty("FOO"); %