java - writer 是原子方法吗？

Question

我想将一些字符串写入文件。所以，我使用了 BufferedWriter 类。由于许多线程倾向于写入该文件，我想知道 write 和 writeLine 方法是否是原子的。

此外，我希望程序将输出写入多个文件，每个文件 100 行(比如 file.txt0、file.txt1，...)。例如

public class Main {
    static ExecutorService exec = Executors.newFixedThreadPool(5);
    BufferedWriter bw;
    public class myWriter implements Runnable {
        String str;
        myWriter (String str) {
            this.str = str;
        }
        public void run() {
            bw.write(str);
            bw.writeLine();
        }
    }
    public static void main(String[] args) {
        bw = new BufferedWriter(new  FileWriter("train.txt"));
        for (String arg: args)
            exec.execute(new myWriter(arg));
        exec.awaitTermination(100000, TimeUnit.MILLISECONDS);
    }
}

有人可以帮助我吗？如果它们不是原子的，我怎样才能使它们成为原子的并避免碰撞？

Answer 1

不，那些不是原子的。

如果你想多次写入同一个文件，使用FileLocks .

try {
    // Get a file channel for the file
    File file = new File("filename");
    FileChannel channel = new RandomAccessFile(file, "rw").getChannel();

    // Use the file channel to create a lock on the file.
    // This method blocks until it can retrieve the lock.
    FileLock lock = channel.lock();

    // Try acquiring the lock without blocking. This method returns
    // null or throws an exception if the file is already locked.
    try {
        lock = channel.tryLock();
    } catch (OverlappingFileLockException e) {
        // File is already locked in this thread or virtual machine
    }

    // Release the lock
    lock.release();

    // Close the file
    channel.close();
} catch (Exception e) {
}