Раскопки в чужих решениях сходу не помогли.
package com.javarush.task.task18.task1808;
/*
Разделение файла
*/
import java.io.*;
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
FileInputStream fi = new FileInputStream(br.readLine());
FileOutputStream fo1 = new FileOutputStream(br.readLine());
FileOutputStream fo2 = new FileOutputStream(br.readLine());
long fileSize = fi.getChannel().size();
byte[] buffer = new byte[1];
while (fi.available() > fileSize/2) {
int count = fi.read(buffer);
fo1.write(buffer,0, count);
}
fo1.close();
while (fi.available() > 0) {
int count = fi.read(buffer);
fo2.write(buffer,0, count);
}
fo2.close();
fi.close();
}
}