halcyondayz halcyondayz - 1 year ago 128
Java Question

Encrypting a large file with AES using JAVA

I've tested my code with files less than this(10mb, 100mb, 500mb) and the encryption works. However, I run in to problems with files greater than 1gb.
I've generated a large file (about 2gb) and I want to encrypt it with AES using JAVA, but I'm running into this error:

"Exception in thread "main" java.lang.OutOfMemoryError: Java heap space"

I've tried increasing available memory by using -Xmx8G, but no dice.
Part of my code is as follows

File selectedFile = new File("Z:\\dummy.txt");
Path path = Paths.get(selectedFile.getAbsolutePath());
byte[] toencrypt = Files.readAllBytes(path);
byte[] ciphertext = aesCipherForEncryption.doFinal(toencrypt);
FileOutputStream fos = new FileOutputStream(selectedFile.getAbsolutePath());

As far as I can tell, the reason it is behaving this way, is that it is trying to read the whole file at once, encipher it, and store it into another byte array instead of buffering and streaming it in. Can anyone help me with some code tips?

I am a beginner to coding, so I don't really know much, any help will be appreciated.

Answer Source

Don't even try to read entire large files into memory. Encrypt a buffer at a time. Just do the standard copy loop with a suitably initialized CipherOutputStream wrapped around the FileOutputStream. You can use this for all files, no need to make a special case out of it. Use a buffer of 8k or more.

EDIT The 'standard copy loop' in Java is as follows:

byte[] buffer = new byte[8192];
int count;
while ((count = in.read(buffer)) > 0)
    out.write(buffer, 0, count);

where in this case out = new CipherOutputStream(new FileOutputStream(selectedFile), cipher).

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