Java Tree to represent filesystem (files/dir) from list of paths

Question

I\'ve a list of paths like this

/mnt/sdcard/folder1/a/b/file1
/mnt/sdcard/folder1/a/b/file2
/mnt/sdcard/folder1/a/b/file3
/mnt/sdcard/folder1/a/b/file4
/mnt/sdc         


        

Answer 1

I would recommend reading up on data structures, particularly trees. In Java, you can represent these by creating a node class that has references to other nodes. For example:

public class Node {
    private Node[] children;
    /* snip other fields */
    public boolean isFile() {
         return children.count == 0;
    }
}

Obviously, you can store your node references anyway you like- arrays or collections will work with non-binary trees.

Given your list of files, you can read these and populate your tree structure.

Answer 2

Seems like you could adapt either a Trie / Radix Trie or a Binary Search Tree to work in either situation. You could augment a Trie to store "folders" as the inner nodes (instead of characters like in a regular Trie) or you could augment a Binary Search Tree to store "folders" as inner nodes (as long as they implement a comparable interface) and "files" as leaf nodes.

My implementation of those structures are linked in the text above.

Answer 3

Thank you for all your answer. I made my working implementation. I think that I will need to improve it in order to make it works better with more caching in adding element to the tree structure.

As I said what I was needing was a structure that allow me to have a "virtual" rappresentation of a FS.

MXMTree.java

public class MXMTree {

    MXMNode root;
    MXMNode commonRoot;

    public MXMTree( MXMNode root ) {
        this.root = root;
        commonRoot = null;
    }

    public void addElement( String elementValue ) { 
        String[] list = elementValue.split("/");

        // latest element of the list is the filename.extrension
        root.addElement(root.incrementalPath, list);

    }

    public void printTree() {
        //I move the tree common root to the current common root because I don't mind about initial folder
        //that has only 1 child (and no leaf)
        getCommonRoot();
        commonRoot.printNode(0);
    }

    public MXMNode getCommonRoot() {
        if ( commonRoot != null)
            return commonRoot;
        else {
            MXMNode current = root;
            while ( current.leafs.size() <= 0 ) {
                current = current.childs.get(0);
            }
            commonRoot = current;
            return commonRoot;
        }

    }


}

MXMNode.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;


public class MXMNode {

    List<MXMNode> childs;
    List<MXMNode> leafs;
    String data;
    String incrementalPath;

    public MXMNode( String nodeValue, String incrementalPath ) {
        childs = new ArrayList<MXMNode>();
        leafs = new ArrayList<MXMNode>();
        data = nodeValue;
        this. incrementalPath = incrementalPath;
    }

    public boolean isLeaf() {
        return childs.isEmpty() && leafs.isEmpty();
    }

    public void addElement(String currentPath, String[] list) {

        //Avoid first element that can be an empty string if you split a string that has a starting slash as /sd/card/
        while( list[0] == null || list[0].equals("") )
            list = Arrays.copyOfRange(list, 1, list.length);

        MXMNode currentChild = new MXMNode(list[0], currentPath+"/"+list[0]);
        if ( list.length == 1 ) {
            leafs.add( currentChild );
            return;
        } else {
            int index = childs.indexOf( currentChild );
            if ( index == -1 ) {
                childs.add( currentChild );
                currentChild.addElement(currentChild.incrementalPath, Arrays.copyOfRange(list, 1, list.length));
            } else {
                MXMNode nextChild = childs.get(index);
                nextChild.addElement(currentChild.incrementalPath, Arrays.copyOfRange(list, 1, list.length));
            }
        }
    }

    @Override
    public boolean equals(Object obj) {
        MXMNode cmpObj = (MXMNode)obj;
        return incrementalPath.equals( cmpObj.incrementalPath ) && data.equals( cmpObj.data );
    }

    public void printNode( int increment ) {
        for (int i = 0; i < increment; i++) {
            System.out.print(" ");
        }
        System.out.println(incrementalPath + (isLeaf() ? " -> " + data : "")  );
        for( MXMNode n: childs)
            n.printNode(increment+2);
        for( MXMNode n: leafs)
            n.printNode(increment+2);
    }

    @Override
    public String toString() {
        return data;
    }


}

Test.java for test code

public class Test {

    /**
     * @param args
     */
    public static void main(String[] args) {

        String slist[] = new String[] { 
                "/mnt/sdcard/folder1/a/b/file1.file", 
                "/mnt/sdcard/folder1/a/b/file2.file", 
                "/mnt/sdcard/folder1/a/b/file3.file", 
                "/mnt/sdcard/folder1/a/b/file4.file",
                "/mnt/sdcard/folder1/a/b/file5.file", 
                "/mnt/sdcard/folder1/e/c/file6.file", 
                "/mnt/sdcard/folder2/d/file7.file", 
                "/mnt/sdcard/folder2/d/file8.file", 
                "/mnt/sdcard/file9.file" 
        };

        MXMTree tree = new MXMTree(new MXMNode("root", "root"));
        for (String data : slist) {
            tree.addElement(data);
        }

        tree.printTree();
    }

}

Please tell me if you have some good advice about improvments :)

Answer 4

I implemented a solution to the challenge myself, it is available as a GitHubGist.

I am representing each node of a filesystem-hierarchy in a DirectoryNode. A helper-method createDirectoryTree(String[] filesystemList) creates a direcotry-tree.

Here is the usage example, which is included in the GitHubGist.

final String[] list = new String[]{
  "/mnt/sdcard/folder1/a/b/file1.file",
  "/mnt/sdcard/folder1/a/b/file2.file",
  "/mnt/sdcard/folder1/a/b/file3.file",
  "/mnt/sdcard/folder1/a/b/file4.file",
  "/mnt/sdcard/folder1/a/b/file5.file",
  "/mnt/sdcard/folder1/e/c/file6.file",
  "/mnt/sdcard/folder2/d/file7.file",
  "/mnt/sdcard/folder2/d/file8.file",
  "/mnt/sdcard/file9.file"
};

final DirectoryNode directoryRootNode = createDirectoryTree(list);

System.out.println(directoryRootNode);

The System.out.println -output is:

  {value='mnt', children=[{value='sdcard', children=[{value='folder1', 
  children=[{value='a', children=[{value='b', children=[{value='file1.file', 
  children=[]}, {value='file2.file', children=[]}, {value='file3.file', 
  children=[]}, {value='file4.file', children=[]}, {value='file5.file', 
  children=[]}]}]}, {value='e', children=[{value='c', 
  children=[{value='file6.file', children=[]}]}]}]}, 
  {value='folder2', children=[{value='d', children=[{value='file7.file', 
  children=[]}, {value='file8.file', children=[]}]}]}, 
  {value='file9.file', children=[]}]}]}

Answer 5

Have a look in new Java 7 - nio2 package. All you need is inside.