The Gathering Write : FileChannel « File « Java Tutorial

1. Java Tutorial
2. File
3. FileChannel

import java.io.File;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class MainClass {
  public static void main(String[] args) {
    try {
      test();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
  private static void test() throws Exception {
    long[] primes = new long[] { 1, 2, 3, 5, 7 };
    File aFile = new File("C:/test/primes.txt");
    FileOutputStream outputFile = null;
    outputFile = new FileOutputStream(aFile);
    FileChannel file = outputFile.getChannel();
    ByteBuffer[] buffers = new ByteBuffer[3];
    buffers[0] = ByteBuffer.allocate(8);
    buffers[2] = ByteBuffer.allocate(8);
    String primeStr = null;
    for (long prime : primes) {
      primeStr = "prime = " + prime;
      buffers[0].putDouble((double) primeStr.length()).flip();
      buffers[1] = ByteBuffer.allocate(primeStr.length());
      buffers[1].put(primeStr.getBytes()).flip();
      buffers[2].putLong(prime).flip();
      file.write(buffers);
      buffers[0].clear();
      buffers[2].clear();
    }
    System.out.println("File written is " + file.size() + "bytes.");
    outputFile.close();
  }
}