Data reading in a jar File (in Java) and counting files

Question

So here is my problem (I read the other answers, but didn't quite get it).

In a group of 4, we have created a game in Java as a University Project. Part of this is creating a *.jar File via Ant. There is several GameBoards saved in GameBoardx.txt Data where x is the number. We want to randomly select one of those. Therefore, every time a GameBoard is loaded, the files in the GameBoard directory are counted in order to generate a random number in the correct range. Our code works perfectly fine when running it from Eclipse. It fails to run from the *.jar File and exits with a NullPointerException.

int number = 0;
int fileCount = new File(new File("").getAbsolutePath()+"/GameBoards/").listFiles().length;
Random rand = new Random();
number = rand.nextInt(fileCount);

These Files are read later on using this:

static String fileName = new File("").getAbsolutePath();
static String line = null;

boolean verticalObstacles[][] = new boolean[16][17];
    int currentLine = 1;
    try {
        FileReader fileReader = new FileReader(fileName+"/GameBoards/Board"+boardNumber+".txt");
        BufferedReader bufferedReader = new BufferedReader(fileReader);
        while ((line = bufferedReader.readLine()) != null){
            if (currentLine <17){
                for (int i=0; i<17; i++){
                    if (line.charAt(i) == '1'){
                        verticalObstacles[currentLine-1][i] = true;
                    } else {
                        verticalObstacles[currentLine-1][i] = false;
                    }

                }
            }
            currentLine ++; 
        } 
        bufferedReader.close();

The rest of the code works with the *.jar File and the *.txt Files are included in it.

The solutions I found were not good for us, because the code has to work with the *.jar File as well as just starting it from Eclipse to pass the test.

What's the solution here to make in work in both?

Answer 1

Problem here is you can not read content of a Jar using File , you shall use java.nio classes to deal with this.

First of all you can read/get count of files from Jar/normal folder by using FileSystem , Path and FileVisitor classes:

Following code will work for both jar as well as IDE

    ClassLoader sysClassLoader = ClassLoader.getSystemClassLoader();
    URI uri = sysClassLoader.getResource("GameBoards").toURI();
    Path gameBoardPath = null;
    if (uri.getScheme().equals("jar")) {
        FileSystem fileSystem = FileSystems.newFileSystem(uri,
                Collections.<String, Object> emptyMap());
        gameBoardPath = fileSystem.getPath("/GameBoards");
    } else {
        gameBoardPath = Paths.get(uri);
    }

    PathVisitor pathVistor = new PathVisitor();
    Files.walkFileTree(gameBoardPath, pathVistor);

    System.out.println(pathVistor.getFileCount());

Following is the code for PathVisitor class

class PathVisitor extends SimpleFileVisitor<Path> {
    private int fileCount = 0;

    @Override
    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs)
            throws IOException {
        fileCount++;
        return FileVisitResult.CONTINUE;
    }

    public int getFileCount() {
        return fileCount;
    }
}

And then you shall read content of specific file by using ClassLoader#getResourceAsStream

    // ADD your random file picking logic here based on file Count to get boardNum
    int boardNum = 1;
    InputStream is = sysClassLoader.getResourceAsStream("GameBoards/Board" + boardNum + ".txt");
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    String line = null;
    while((line=reader.readLine())!=null) {
        System.out.println(line);
    }

Hope this resolves your concerns and helps you in right direction.