java - Write big files using RandomAccessFile class

Question

I need to copy big files (GBs) into another file (the container), and I was wondering about performance and ram use.

Reading the entire source file like the following:

RandomAccessFile f = new RandomAccessFile(origin, "r");
originalBytes = new byte[(int) f.length()];
f.readFully(originalBytes);

And later on, copy everything into the container like this:

RandomAccessFile f2 = new RandomAccessFile(dest, "wr");
f2.seek(offset);
f2.write(originalBytes, 0, (int) originalBytes.length);

does everything in memory, correct? So copying big files can have an impact on memory and can result in an OutOfMemory Exception?

Is it better to read the original file bytes by bytes instead of entirely? In that case how should I have to proceed? Thank you in advance.

EDIT:

Following the answer of mehdi maick I finally found the solution: I can use RandomAccessFile as destination as I wanted, and because RandomAccessFile has a method "getChannel" that returns a FileChannel I can pass that to the following method that will do the copy (32KB at time) of the file in the position of the destination I want:

     public static void copyFile(File sourceFile, FileChannel destination, int position) throws IOException {
            FileChannel source = null;
            try {
                source = new FileInputStream(sourceFile).getChannel();
                destination.position(position);
                int currentPosition=0;
                while (currentPosition < sourceFile.length())
                    currentPosition += source.transferTo(currentPosition, 32768, destination);
            } finally {
                if (source != null) {
                    source.close();
                }

            }
        }

标签： javarandomaccessfile

Answer 1

尝试使用异步 nioChannel

    public void copyFile(String src, String target) {
        final String fileName = getFileName(src);
        try (FileChannel from = (FileChannel.open(Paths.get(src), StandardOpenOption.READ));
                FileChannel to = (FileChannel.open(Paths.get(target + "/" + fileName), StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE))) {
            transfer(from, to, 0l, from.size());
        }
    }

    private String getFileName(final String src) {
        File file = new File(src);
        if (file.isFile()) {
            return file.getName();
        } else {
            throw new RuntimeException("src is not a valid file");
        }
    }

    private void transfer(final FileChannel from, final FileChannel to, long position, long size) throws IOException {
        while (position < size) {
            position += from.transferTo(position, Constants.TRANSFER_MAX_SIZE, to);
        }
    }

这将创建一个读写异步通道，并有效地将数据从第一个传输到第二个。