Why does my test filesystem only work in memory?

Question

I am working on a concept of a filesystem for a program. I am writing in Java (using JDK 7 u17).

To get started I built off of some tutorial that were showing my how to create a zip based filesystem using the FileSystemProvider class.

When I execute the code I have it do similar task to the examples which is copy a text file from the my desktop and place it in the zip file. The problem is once it copies the file it does not write it into the zip file, it seems to leave the file in memory which is destroyed when the program is terminated.

The problem is I cannot understand why, as far as I can tell everything looks to be in order but something is clearly not!

Oh yeah the same thing goes for directories too. If I tell the filesystem to make a new directory it just creates it in memory and there is nothing in the zip file.

Anyhow here is my working code;

import java.io.IOException;
import java.net.URI;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.Map;

public class Start {

    public static void main(String[] args) {

        Map <String, String> env = new HashMap<>();
        env.put("create", "true");
        env.put("encoding", "UTF-8");

        FileSystem fs = null;

        try {
            fs = FileSystems.newFileSystem(URI.create("jar:file:/Users/Ian/Desktop/test.zip"), env);
        } catch (IOException e) {
            e.printStackTrace();
        }

        Path externalTxtFile = Paths.get("/Users/Ian/Desktop/example.txt");
        Path pathInZipFile = fs.getPath("/example.txt");

        try {
            Files.createDirectory(fs.getPath("/SomeDirectory"));
        } catch (IOException e) {
            e.printStackTrace();
        }

        if (Files.exists(fs.getPath("/SomeDirectory"))) {
            System.out.println("Yes the directory exists in memory.");
        } else {
            System.out.println("What directory?");
        }       

        // Why is the file only being copied into memory and not written out the jar/zip archive?
        try {
            Files.copy(externalTxtFile, pathInZipFile);
        } catch (IOException e) {
            e.printStackTrace();
        }

        // The file clearly exists just before the program ends, what is going on?
        if (Files.exists(fs.getPath("/example.txt"))) {
            System.out.println("Yes the file has been copied into memory.");
        } else {
            System.out.println("What file?");
        }

    }

}

@TAS ...Wow I feel foolish and the example I was following is apparently incomplete. Closing the filesystem solved my problem. Thanks! — AtomicPorkchop, Mar 25 '13 at 07:53

score 0 · Answer 1 · answered Apr 26 '14 at 11:35

I just want to add something. Perhaps the example that you found was incomplete (I can not check since you do not references it) but in all examples I found the FileSystem instance is closed properly.

The FileSystem abstract class implements Closeable, so the close() method is called (automatically) leaving the try in the following code:

try (final FileSystem fs = FileSystems.newFileSystem(theUri, env)) {
    /* ... do everything you want here ; do not need to call fs.close() ... */
}

http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

Why does my test filesystem only work in memory?

1 Answers1