I am learning multithreading in Java, and I have a task to copy a file using 2+ threads.
File extension does not matter. So I tried to do it in 2 threads. In the first thread, I copy first half of the file, in the second thread - the second one. I tried to save parts in a byte array, and after go to the main thread and use ByteArrayOutputStream to concatenate these arrays & save a copy of the source file. But it works once-twice in three-six times. I have no idea what's wrong. How to copy a file in multiple threads using Java
public class FirstThread implements Runnable {
private byte[] part1thread;
private RandomAccessFile file;
public FirstThread(RandomAccessFile file, int byteArraySize) {
this.file = file;
this.part1thread = new byte[byteArraySize];
}
public void run() {
try {
System.out.println("Start the first thread.");
file.read(part1thread, 0, part1thread.length);
System.out.println("I am the first thread and I read first part1thread of the file you gave me.");
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
RandomAccessFile fileOutputWrite = new RandomAccessFile("copy_", "rw");
System.out.println("First threads results writing...");
outputStream.write(this.part1thread);
System.out.println("output 1 thread: " + outputStream);
fileOutputWrite.write(this.getPart1thread(), 0, this.getPart1thread().length);
fileOutputWrite.close();
outputStream.close();
Main.setCountDownLatch();
} catch (IOException e) {
e.printStackTrace();
}
}
public byte[] getPart1thread() {
return part1thread;
}
}
public class SecondThread implements Runnable {
private byte[] part2thread;
private RandomAccessFile file;
private long tempBytesSize;
public SecondThread(RandomAccessFile file, int arrayFullSize) {
this.file = file;
tempBytesSize = arrayFullSize % 2 == 0 ? arrayFullSize/2 : arrayFullSize/2 + 1;
System.out.println(arrayFullSize % 2 == 0);
this.part2thread = new byte[(int)tempBytesSize];
}
public void run() {
try {
System.out.println("Start the second thread.");
file.seek(part2thread.length - 1);
System.out.println(tempBytesSize);
file.read(part2thread, 0, (int)tempBytesSize);
System.out.println("I am the second thread and I read second part2thread of the file you gave me.");
RandomAccessFile fileOutputWrite = new RandomAccessFile("copy_", "rw");
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
fileOutputWrite.seek(fileOutputWrite.length() - 1);
System.out.println("Second threads results writing..");
outputStream.write(this.getPart2thread());
System.out.println("output 2 thread: " + outputStream);
fileOutputWrite.write(this.getPart2thread(), 0, this.getPart2thread().length);
fileOutputWrite.close();
outputStream.close();
Main.setCountDownLatch();
} catch (IOException e) {
e.printStackTrace();
}
}
public byte[] getPart2thread() {
return part2thread;
}
}
public class Main {
private static volatile CountDownLatch countDownLatch;
public synchronized static void main(String[] args) throws IOException {
countDownLatch = new CountDownLatch(2);
Scanner scanner = new Scanner(System.in);
System.out.println("Enter file name with extension");
String fileName = scanner.nextLine();
RandomAccessFile file = null;
long partByteSize = 0;
try {
file = new RandomAccessFile(fileName, "r");
partByteSize = file.getChannel().size() / 2;
} catch (FileNotFoundException e) {
System.out.println("File not found!");
System.exit(-1);
} catch (IOException e) {
System.out.println("An error has been occured. Cannot work with file.");
System.exit(-1);
}
ExecutorService pool = Executors.newFixedThreadPool(2);
FirstThread firstThread = new FirstThread(file, (int) partByteSize);
SecondThread secondThread = new SecondThread(file, (int) file.getChannel().size());
pool.submit(firstThread);
pool.submit(secondThread);
try {
countDownLatch.await();
} catch (InterruptedException e) {
System.out.println("Unexpected error.");
System.exit(-1);
}
System.out.println("Return flow control to the main thread");
ByteArrayOutputStream outputStream;
file.close();
System.exit(0);
}
public static void setCountDownLatch() {
Main.countDownLatch.countDown();
}
}
I tried with *.pdf & *.txt files. *.pdf copies does not open, *.txt files: when I copy only the first or the second half, it works well. But when I tried to copy two parts one by one, it works SOMETIMES. I have no idea how to fix it.
