Android: Using the ParcelFileDescriptor returned from UiAutomation.executeShellCommand() in InstrumentationTestCase

Question

I've written a generic shellCommand function for my InstrumentationTestCase subclass. The call to executeShellCommand works (the command is executed), but I'm doing something wrong with the returned ParcelFileDescriptor, because it seems to return rubbish. Here's my generic shellCommand function -

public String shellCommand(String str)
{
    UiAutomation uia = getInstrumentation().getUiAutomation();
    ParcelFileDescriptor pfd;
    FileDescriptor fd;
    InputStream is;
    byte[] buf = new byte[1024];
    String outputString = null;

    try
    {
        pfd = uia.executeShellCommand(str);
        fd = pfd.getFileDescriptor();
        is = new BufferedInputStream(new FileInputStream(fd));
        is.read(buf, 0, buf.length);
        outputString = buf.toString();
        Log.d(TAG, String.format("shellCommand: buf '%s'",outputString));
        is.close();
    }
    catch(IOException ioe)
    {
        Log.d(TAG, "shellCommand: failed to close fd");
    }
    return outputString;
}

And here's a snippet showing me calling it -

String output = shellCommand("ls -al /");
Log.d(TAG, String.format("root dir = {%s}", output)); 

I was hoping to receive the command's output string (in this example, a list of top-level directories). Instead I see the following log -

shellCommand: buf '[B@1391fd8d'

I'm not great with Java, I just use it to write some automated tests. I'm obviously doing something wrong with the ParcelFileDescriptor or BufferedInputStream, can someone please explain what?

Answer 1

The toString() method doesn't actually convert the contents of a byte array to a String. It returns "a string representation of the object". In this case, '[B@1391fd8d' means "the byte array whose hashcode is 1391fd8d" - not very useful is it?

You can convert a byte[] to a String by using the new String(byte[]) constructor.

However it's probably easier to use BufferedReader.readLine() to get a String directly from each line of output.