Build json array of file tree structure.

FileTreeBuilder.java

import android.content.Context;
import android.os.Environment;
import android.util.Log;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.File;
import java.io.FileOutputStream;
import java.util.ArrayList;
import java.util.Arrays;

public class FileTreeBuilder {

    private static FileTreeBuilder mBuilder;
    private static final String NAME = "name";
    private static final String TYPE = "type";
    private static final String CONTENTS = "contents";
    private static final String DIRECTORY = "directory";
    private static final String FILE = "file";
    private static final String FILE_SIZE = "fileSize";
    private static final String TAG = "FileTreeBuilder";

    public FileTreeBuilder() {
    }

    public static FileTreeBuilder getInstance() {
        if (mBuilder == null) {
            mBuilder = new FileTreeBuilder();
        }
        return mBuilder;
    }

    public JSONArray getDirectoryContents(File directory) {
        JSONArray contentsArray = new JSONArray();

        if (directory.isDirectory()) {
            File[] files = directory.listFiles();
            Arrays.sort(files);

            ArrayList <File> directoryList = new ArrayList<>();
            ArrayList <File> fileList = new ArrayList<>();

            for(int i = 0; i < files.length; i++){
                if(files[i].isDirectory()){
                    directoryList.add(files[i]);
                }else {
                    fileList.add(files[i]);
                }
            }
            directoryList.addAll(fileList);
            files = directoryList.toArray(files);


            for (int i = 0; i < files.length; i++) {

                File file = files[i];
                JSONObject fileObject = new JSONObject();

                try {
                    fileObject.put(NAME, file.getName());
                    fileObject.put(TYPE, getType(file));
                    fileObject.put(FILE_SIZE, getFileSize(file));
                    fileObject.put(CONTENTS, getDirectoryContents(file));
                } catch (JSONException e) {
                    e.printStackTrace();
                }
                contentsArray.put(fileObject);

            }
        }
        return contentsArray;
    }

    public JSONArray build() {
        JSONArray fileTreeArray = new JSONArray();

        File rootDirectory = Environment.getExternalStorageDirectory();
        JSONObject rootObject = new JSONObject();

        try {
            rootObject.put(NAME, rootDirectory.getAbsolutePath());
            rootObject.put(TYPE, getType(rootDirectory));
            rootObject.put(FILE_SIZE, getFileSize(rootDirectory));
            rootObject.put(CONTENTS, getDirectoryContents(rootDirectory));
        } catch (JSONException e) {
            e.printStackTrace();
        }

        fileTreeArray.put(rootObject);
        return fileTreeArray;
    }

    private String getType(File file) {
        String type = FILE;
        if (file.isDirectory()) {
            type = DIRECTORY;
        }
        return type;
    }

    public void saveFile(Context context, String content) {
        String filename = "aswin.txt";
        String fileContents = content;
        FileOutputStream outputStream;

        try {
            outputStream = context.openFileOutput(filename, Context.MODE_PRIVATE);
            outputStream.write(fileContents.getBytes());
            outputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private String getFileSize(File file) {
        if (!file.isDirectory()) {
            int fileSizeInBytes = Integer.parseInt(String.valueOf(file.length()));
            if (fileSizeInBytes > 1024) {
                if (fileSizeInBytes > (1024 * 1024)) {
                    return fileSizeInBytes / (1024 * 1024) + " MB";
                } else {
                    return fileSizeInBytes / (1024) + " KB";
                }
            } else {
                return fileSizeInBytes + " bytes";
            }
        } else {
            return "0 bytes";
        }
    }
    
}