How to write data to a file very quickly??

Question

Java

I write the csv file with data, 1.000.000 lines. For this I use bufferewriter. If you write 1000 lines, it's fast, if 10,000, then it's generally slow. How can you speed up the process?

Answer 1

In any case, it will not work quickly, since this is an IO operation on the disk. Much depends on the disk itself.
I recommend trying Memory Mapped Files, but you need to know how much you will write in order to reserve space.

byte[] buffer = new byte[4096];
int numOfLines = 1000000;

FileChannel rwChannel = new RandomAccessFile("textfile.txt", "rw").getChannel();
ByteBuffer wrBuf = rwChannel.map(FileChannel.MapMode.READ_WRITE, 0, buffer.length * numOfLines);
for (int i = 0; i < numOfLines; i++)
{
    wrBuf.put(buffer);
}
rwChannel.close();