AsyncFileWriteMain.java

package me.masahito;


import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousFileChannel;
import java.nio.channels.CompletionHandler;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.concurrent.CountDownLatch;

public class AsyncFileWriteMain {

    private static final int LINE_SIZE = 10;
    private static final CountDownLatch responseWaiter = new CountDownLatch(10);

    public static void main(String[] args) throws IOException {
        final Path path = Paths
                .get("path_to_file");
        try (final AsynchronousFileChannel channel = AsynchronousFileChannel.open(
                path, StandardOpenOption.WRITE, StandardOpenOption.CREATE)) {
            System.out.println("Start to write");


            final CompletionHandler<Integer, String> handler = new CompletionHandlerImpl();

            for (int i = 0, position = 0; i < LINE_SIZE; i++) {
                final String message = "Hello World-" + Integer.toString(i) + "\n";
                // Buffer、書き込み位置、アタッチメント、ハンドラを与えて書き込み処理実行
                channel.write(ByteBuffer.wrap(message.getBytes()), position, getAttachment(i), handler);
                // 次にメッセージを書き込む位置を設定
                position += message.length();
            }
            responseWaiter.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /*
     * Attachmentはサンプルなので適当なメッセージを返す。
     */
    private static String getAttachment(int i) {
        return (i + 1) == 1 ? Integer.toString(i + 1) + " time" : Integer.toString(i + 1) + " times";
    }

    private static final class CompletionHandlerImpl implements CompletionHandler<Integer, String> {

        @Override
        public void completed(Integer result, String attachment) {
            System.out.println("[Completed to write] Current thread : " + Thread.currentThread().getId() + " Attachment : " + attachment + " Written bytes : " + result);
            responseWaiter.countDown();
        }

        @Override
        public void failed(Throwable e, String attachment) {
            System.out.println("[Failed to write] Current thread : " + Thread.currentThread().getId() + " Attachment : " + attachment + " Exception : " + e);

        }

    }

}