Java: InputStream too slow to read huge files

Question

I have to read a 53 MB file character by character. When I do it in C++ using ifstream, it is completed in milliseconds but using Java InputStream it takes several minutes.

Answer 1

I would try this

// create the file so we have something to read.
final String fileName = "1.2.fasta";
FileOutputStream fos = new FileOutputStream(fileName);
fos.write(new byte[54 * 1024 * 1024]);
fos.close();

// read the file in one hit.
long start = System.nanoTime();
FileChannel fc = new FileInputStream(fileName).getChannel();
ByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
while (bb.remaining() > 0)
    bb.getLong();
long time = System.nanoTime() - start;
System.out.printf("Took %.3f seconds to read %.1f MB%n", time / 1e9, fc.size() / 1e6);
fc.close();
((DirectBuffer) bb).cleaner().clean();

prints

Took 0.016 seconds to read 56.6 MB