determine whether android asset entry is a file or directory

Question

Hej,

I have some data shipped out with the app which shall be copied on the external storage. It's nested in a couple of subfolders and I'd like to copy the whole structure.

I'm having a hard time getting a File object for any ressource in /assets. But I think I'm depended on that 'cause I need something like File.isDirectory() to determine if I have to start copying or dive deeper into the system.

My first approach was using Assets Manager but it seems that class is not providing the information I need. The most promising why was to obtain an AssetFileDescriptorand go down to a [FileDescriptor][2]. However non of them seems to have a isDirectory-method.

So my other approach is straight forward: Creating a File Object and be happy. However it seems like I'm running in this problem of lacking a proper path to instance the file object. I'm aware of file://android_asset but it doesn't seem to work for the fileconstructor.

My last idea would to utilise the InputStream (which I need for copying anyway) and somehow filter the byte for a significant bit which indicates this resource to be a directory. That's a pretty hacky solution and probably right in the hell of ineffectiveness but I don't see another way to get around that.

Answer 1

I had the same problem. At some point I realized that list() is really slow (50ms on every call), so i'm using a different approach now:

I have an (eclipse) ant-builder which creates an index-file everytime my asset-folder changes. The file just contains one file-name per line, so directories are listed implicitely (if they are not empty).

The Builder:

<?xml version="1.0"?>
<project default="createAssetIndex">
    <target name="createAssetIndex">
        <fileset id="assets.fileset" dir="assets/" includes="**"
            excludes="asset.index" />
        <pathconvert pathsep="${line.separator}" property="assets"
            refid="assets.fileset">
            <mapper>
                <globmapper from="${basedir}/assets/*" to="*"
                    handledirsep="yes" />
            </mapper>
        </pathconvert>
        <echo file="assets/asset.index">${assets}</echo>
    </target>
</project>

The class which loads asset.index into a List of Strings, so you can do arbitrary stuff with it, fast:

import android.content.ContextWrapper;

import com.google.common.collect.ImmutableList;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;

import java.util.Scanner;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * uses asset.index file (which is pregenerated) since asset-list()s take very long
 *
 */
public final class AssetIndex {

    //~ Static fields/initializers -------------------------------------------------------------------------------------

    private static final Logger L = LoggerFactory.getLogger(AssetIndex.class);

    //~ Instance fields ------------------------------------------------------------------------------------------------

    private final ImmutableList<String> files;

    //~ Constructors ---------------------------------------------------------------------------------------------------

    public AssetIndex(final ContextWrapper contextWrapper) {

        ImmutableList.Builder<String> ib = ImmutableList.builder();

        L.debug("creating index from assets");

        InputStream in  = null;
        Scanner scanner = null;
        try {
            in          = contextWrapper.getAssets().open("asset.index");
            scanner     = new Scanner(new BufferedInputStream(in));

            while (scanner.hasNextLine()) {
                ib.add(scanner.nextLine());
            }

            scanner.close();
            in.close();

        } catch (final IOException e) {
            L.error(e.getMessage(), e);
        } finally {
            if (scanner != null) {
                scanner.close();
            }
            if (in != null) {
                try {
                    in.close();
                } catch (final IOException e) {
                    L.error(e.getMessage(), e);
                }
            }
        }

        this.files = ib.build();
    }

    //~ Methods --------------------------------------------------------------------------------------------------------

    /* returns the number of files in a directory */
    public int numFiles(final String dir) {

        String directory = dir;
        if (directory.endsWith(File.separator)) {
            directory = directory.substring(0, directory.length() - 1);
        }

        int num = 0;
        for (final String file : this.files) {
            if (file.startsWith(directory)) {

                String rest = file.substring(directory.length());
                if (rest.charAt(0) == File.separatorChar) {
                    if (rest.indexOf(File.separator, 1) == -1) {
                        num = num + 1;
                    }
                }
            }
        }

        return num;
    }
}

Answer 2

In my specific case, regular files have a name like filename.ext, while directories only have a name, without extension, and their name never contains the "." (dot) character. So a regular file can be distinguished from a directory by testing its name as follows:

filename.contains(".")

If this your case too, the same solution should work for you.

Answer 3

list() on AssetManager will probably give a null / zero length array / IOException if you try to get a list on a file, but a valid response on a directory.

But otherwise it should be file:///android_asset (with 3 /)