Two Java methods for easy writing and reading bytes in files
From your "reinventing-the-wheel" tag, I assume you're already aware of Guava's and Apache Commons' utilities. So my only nitpick is that the int cast might be clearer if it was closer to the size check:

long sizeLong = file.length();
checkSize(sizeLong);
int size = (int)sizeLong;


Or if you want to be a little more "clever":

int size = checkSize(file.length());
//...
private static final int checkSize(long size) {
    //...
    return (int)size;
}