Question

I am trying to copy a large pdf-file (3.7 mb) from my raw-folder to the external cache directory.

I a using the following piece of code:

int i = 0;
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) 
        {           
            InputStream input = getResources().openRawResource(pdfs[i]);
            File file = new File(Environment.getExternalStorageDirectory(), "/Android/data/eu.app/cache/" + pdfNames[i]);

            if(!file.exists())
            {
                try
                {
                    new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/Android/data/eu.app/cache").mkdirs();
                    FileOutputStream fos = new FileOutputStream(file.toURI().getPath(), false);

                    OutputStream os = new BufferedOutputStream(fos);



                    byte[] buffer = new byte[1024];
                    int byteRead = 0;


                    while ((byteRead = input.read(buffer)) != -1) {

                            os.write(buffer, 0, byteRead);
                    }

                    fos.close();

                }
                catch(Exception ex)
                {
                    Log.d("storage", ex.getMessage()); 

                }
            }               
        }
        else
        {

        }

I don’t get any errors, but the output-file is a few bytes smaller than the original and cannot be opened.
What do I need to do to fix this?

Answer 1

I think the main issue is that you close fos while you should close os. You also need to put the close operation in a finally block.

Update (now with a full keyboard ;)): You close the file stream (fos) before the buffered stream is flushed. What you should do is to close the buffered stream (os), and that will in turn flush its buffer and write those bytes that are missing, and then it will automatically close the underlying file stream. To fix it change fos.close() into os.close().

In addition, to make sure that you always close the stream you should place the close operation in a finally block. A typical pattern is the following:

BufferedInputStream in = null;
try {
    in = new BufferedInputStream(anInputStream);

    BufferedOutputStream out = null;
    try {
        out = new BufferedOutputStream(new FileOutputStream(aFile));
        // Read and write what you should write
    }
    finally {
        if (out != null) out.close();
    }
} finally {
    if (in != null) in.close();
}

You can easily add an input stream, but be careful to make sure all streams are closed. This can be handled by nesting finally blocks or nesting try-catch blocks inside the finally block.

Either you throw an IOException from this method and handle it outside (often preferred), or you wrap the above code in a new try-catch statement and handle it there. However, handling it within the method mixes UI with logic and the code is often clearer separating UI and logic.

A final note: 1024 is rather small. Play with different values. On the other hand the buffered stream will handle the buffering for you.