How to split file into chunks while still writing into it?

Question

I tried to create byte array blocks from file whil the process was still using the file for writing. Actually I am storing video into file and I would like to create chunks from the same file while recording.

The following method was supposed to read blocks of bytes from file:

private byte[] getBytesFromFile(File file) throws IOException{ InputStream is = new FileInputStream(file); long length = file.length(); int numRead = 0; byte[] bytes = new byte[(int)length - mReadOffset]; numRead = is.read(bytes, mReadOffset, bytes.length - mReadOffset); if(numRead != (bytes.length - mReadOffset)){ throw new IOException("Could not completely read file " + file.getName()); } mReadOffset += numRead; is.close(); return bytes; }

But the problem is that all array elements are set to 0 and I guess it is because the writing process locks the file.

I would bevery thankful if anyone of you could show any other way to create file chunks while writing into file.

Does your own application write the video file (you've written it)? Or do you try to chunk the output of a foreign application? — Eduard Wirch
– Eduard Wirch, Commented Oct 6, 2009 at 16:04

Niko Gamulin · Accepted Answer · 2009-10-07 08:52:02Z

Solved the problem:

private void getBytesFromFile(File file) throws IOException { FileInputStream is = new FileInputStream(file); //videorecorder stores video to file java.nio.channels.FileChannel fc = is.getChannel(); java.nio.ByteBuffer bb = java.nio.ByteBuffer.allocate(10000); int chunkCount = 0; byte[] bytes; while(fc.read(bb) >= 0){ bb.flip(); //save the part of the file into a chunk bytes = bb.array(); storeByteArrayToFile(bytes, mRecordingFile + "." + chunkCount);//mRecordingFile is the (String)path to file chunkCount++; bb.clear(); } } private void storeByteArrayToFile(byte[] bytesToSave, String path) throws IOException { FileOutputStream fOut = new FileOutputStream(path); try { fOut.write(bytesToSave); } catch (Exception ex) { Log.e("ERROR", ex.getMessage()); } finally { fOut.close(); } }

Hakanai · Accepted Answer · 2009-10-03 10:28:55Z

If it were me, I would have it chunked by the process/thread writing to the file. This is how Log4j seems to do it, at any rate. It should be possible to make an OutputStream which automatically starts writing to a new file every N bytes.

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