Java Out of Memory Error during Encryption

Question

I am using AES to encrypt files. The problem first came when i tried to encrypt a large file. So i did some reading online and figured that i need to use a buffer and only e

Answer 1

As you're iterating over the file, keep a counter to track the number of bytes:

int encryptedBytesSize = 0;
for(int i = 0; i < bufferedFile.size(); i++) {
    resultByteList.add(cipher.doFinal(bufferedFile.get(i)));
    encryptedBytesSize += resultByteList.get(resultByteList.size() - 1).length;
}

Then use the constructor which takes a size parameter to create the output buffer:

ByteArrayOutputStream baos = new ByteArrayOutputStream(encryptedBytesSize);

This will avoid the internal buffer from having to grow. Growth could be non-linear so as more bytes are added each iteration even more space is allocated the next time it grows.

But this still might not work, depending on the file size. Another approach would be to:

1. Read a little chunk of the unencrypted file
2. Encrypt the chunk
3. Write to the encrypte file

This avoids having all of the regular and encrypted files in memory at the same time.