Creating and Storing Log File on device in Android

Question

I am planning to automate the testing of an application by creating a log to store some results of execution of the app and latter on parse it using a piece of python code and plot a graph.

The application is a WiFi fingerprinter i.e it collects info such as mac id, rss(recieved signal strength and rank(normalized rss) about the wifi devices in the surrounding environment. So to test this application I would have to take it to the location and record the results(as of now manually). So logcat wouldn't serve the purpose.

Automation requires 1. Storing the log in the device 2. Access to the log file in the system through usb

Format of the Log file:

Snapshot: 1
Fingerprint: 1, Rank: 0.23424, Boolean: true
Fingerprint: 2, Rank: 0.42344, Boolean: false
Fingerprint: 3, Rank: 0.23425, Boolean: true

Snapshot: 2
Fingerprint: 1, Rank: 0.75654, Boolean: false
Fingerprint: 2, Rank: 0.23456, Boolean: true
Fingerprint: 3, Rank: 0.89423, Boolean: true 

................

Now I know there are basically 3 approaches for persistent storage(SharedPrefs wouldn't suit this scenario anyway). I tried Internal Storage, but even after setting the mode of the file as MODE_WORLD_READABLE it was impossible to read the file using Device File Explorer in Eclipse.

I am still wary of using external storage for storing the log. Any tutorial on how to write to a file in usb of the device will definitely help.

I thought of structuring the data to be stored so as to use SQLite for storage. But this establishing many unnecessary relations(foreign and domestic) between data and make it complex. If there is no way around, then here be dragons.

Basically I want to write to a file(easier I suppose) in the device and latter on read it in my system by connecting to it via usb. Any help on how to do it would be much appreciated.

Answer 1

Wary or not, External Storage still may be the only way to go. Without root access on the device, you can't really get at anything "Internal" unless you're going to be okay with reading within an application on the device. The docs provide pretty solid guidelines for where to create external files, and if you are using API Level 8 or higher, there are a couple of extra functions that can be used. I'm sure you know this page, but here it is anyway: http://developer.android.com/guide/topics/data/data-storage.html#filesExternal

If you're in need of any file io example code... I think I could dig some up...

EDIT - I would start by following the guidelines in the above docs to first confirm the state of the storage. I unfortunately don't have any experience with appending a file in Java, so someone else would definitely be more qualified to answer. This doesn't cover appending, but I have a backup routine in one of my personal apps that looks something like this.

    File backupPath = Environment.getExternalStorageDirectory();

    backupPath = new File(backupPath.getPath() + "/Android/data/com.maximusdev.bankrecord/files");

    if(!backupPath.exists()){
        backupPath.mkdirs();
    }

    FileOutputStream fos;
    try {
        fos = new FileOutputStream(backupPath.getPath() + "/recordsbackup.txt");

        if(okaytowrite){
            for(int i = 0; i < count; ++i){
                entry = adapter.getItem(i);
                fos.write(entry.toString().getBytes());
                fos.write("\n".getBytes());
                fos.write(String.valueOf(entry.dateTime).getBytes());
                fos.write("\n".getBytes());
                fos.write(String.valueOf(entry.sign).getBytes());
                fos.write("\n".getBytes());
                fos.write(String.valueOf(entry.cleared).getBytes());
                fos.write("\n".getBytes());
                fos.write(String.valueOf(entry.transDate).getBytes());
                fos.write("\n".getBytes());
                fos.write(entry.category.getBytes());
                fos.write("\n".getBytes());
            }
        }
        fos.close();

        Toast.makeText(this, "Backup Complete", Toast.LENGTH_SHORT).show();

    } catch (FileNotFoundException e) {

        e.printStackTrace();

        AlertDialog.Builder delmessagebuilder = new AlertDialog.Builder(this);

        delmessagebuilder.setCancelable(false);

        delmessagebuilder.setMessage("File Access Error");

        delmessagebuilder.setNeutralButton("Okay", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
                dialog.dismiss();
            }
        });

        delmessagebuilder.create().show();

    } catch (IOException e) {

        e.printStackTrace();

        AlertDialog.Builder delmessagebuilder = new AlertDialog.Builder(this);

        delmessagebuilder.setCancelable(false);

        delmessagebuilder.setMessage("File Access Error");

        delmessagebuilder.setNeutralButton("Okay", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
                dialog.dismiss();
            }
        });

        delmessagebuilder.create().show();
    }

Once I'm ready to write, I'm pulling a custom object (entry) out of an ArrayAdapter (adapter) and converting field valuse to strings and using getBytes() to pass to the FileOutputStream write function. I've done some research and there are quite a few other options for file writing in Java/Android... the FileWriter Class for instance, so it bears further research.