See InputSteram.read(byte[]) for reading bytes at a time.
Example code:
try {
File file = new File("myFile");
FileInputStream is = new FileInputStream(file);
byte[] chunk = new byte[1024];
int chunkLen = 0;
while ((chunkLen = is.read(chunk)) != -1) {
// your code..
}
} catch (FileNotFoundException fnfE) {
// file not found, handle case
} catch (IOException ioE) {
// problem reading, handle case
}