The following reads bytes in a file and writes these bytes as characters in another file using Writer. I have extracted it from this discussion
String filePath = Display.getInstance().getDatabasePath("TestDB.db");
FileSystemStorage fss = FileSystemStorage.getInstance();
InputStream is = fss.openInputStream(filePath);
byte[] plainBytes = Util.readInputStream(is);
//encrypt database file content
Log.p("Starting file encryption...");
byte[] cipherByteArray = FilesCipher.encryptFile(plainBytes);
Log.p("Done encrypting file");
ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(cipherByteArray);
String encryptedFilePath = fss.getAppHomePath() + "EncryptedDB.db";
Log.p("Writing to new a file started...");
try (Writer w = new OutputStreamWriter(fss.openOutputStream(encryptedFilePath), "ISO-8859-1")) {
int nextChar = byteArrayInputStream.read();
while (nextChar > -1) {
char[] charArray = {(char) nextChar};
w.write(charArray);
nextChar = byteArrayInputStream.read();
}
Log.p("Done writing to a new file");
} catch (Exception e) {
Log.p("Error " + e);
}
If file size of the file being read (Eg TestDB.db) is small (less than 500KB), In Simulator & Device, the Writer writes to the new file (Eg. EncryptedDB.db) very fast.
If the file is large eg. 3MB, In Simulator it's written very fast to the new file. But in a device it takes more than 2 minutes. I tested in Android 10.
I have confirmed that encryption is very fast since even when file is large, Log.p("Writing to new a file started..."); is executed within 2 Seconds even in the device.
When file is large, in a Simulator Log.p("Done writing to a new file"); is executed within seconds but in a device it takes more than 3 minutes. This means Writer is slow in a device.
Writer doesn't have a function to write bytes directly.
How can Writer speed be enhanced in devices?
From this Shared Files blog it's also possible to write file bytes directly using OutputStream. That is
OutputStream outputStream = fss.openOutputStream(encryptedFilePath);
outputStream.write(cipherByteArray);
A file of size 11.9MB (It has images stored as blob), results to the following log in Android Studio. Encryption completes in 2 sec & writes to the new file in milliseconds
2024-07-28 11:14:21.109 30329-30415 {App Name} D [EDT] 0:0:30,313 - Starting file encryption...
2024-07-28 11:14:23.733 30329-30415 {App Name} D [EDT] 0:0:32,937 - File encryption DONE
2024-07-28 11:14:23.735 30329-30415 {App Name} D [EDT] 0:0:32,940 - Saving encrypted file...
2024-07-28 11:14:23.767 30329-30415 {App Name} D [EDT] 0:0:32,971 - DONE Saving encrypted file