Java by API/java.nio.channels/FileChannel

FileChannel: close()

   
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String args[]) {
    RandomAccessFile randomAccessFile;
    FileChannel fileChannel;
    ByteBuffer byteBuffer;
    try {
      randomAccessFile = new RandomAccessFile("test.txt", "rw");
      fileChannel = randomAccessFile.getChannel();
      byteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, 26);
      for (int i = 0; i < 10; i++)
        byteBuffer.put((byte) ("A" + i));
      fileChannel.close();
      randomAccessFile.close();
    } catch (IOException exc) {
      System.out.println(exc);
      System.exit(1);
    }
  }
}

FileChannel: lock(long position, long size, boolean shared)

 
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
public class Main {
  public static void main(String[] argv) throws Exception {
    String filename = "test.dat";
    RandomAccessFile raf1 = new RandomAccessFile(filename, "rw");
    FileChannel fc1 = raf1.getChannel();
    RandomAccessFile raf2 = new RandomAccessFile(filename, "rw");
    FileChannel fc2 = raf2.getChannel();
    System.out.println("Grabbing first lock");
    FileLock lock1 = fc1.lock(0L, Integer.MAX_VALUE, false);
    System.out.println("Grabbing second lock");
    FileLock lock2 = fc2.lock(5, 10, false);
    System.out.println("Exiting");
  }
}

FileChannel: map(MapMode mode, long position, long size)

   
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.IntBuffer;
import java.nio.channels.FileChannel;
public class Main {
  public static void main(String[] args) throws IOException {
    FileChannel fc = new RandomAccessFile(new File("temp.tmp"), "rw").getChannel();
    IntBuffer ib = fc.map(FileChannel.MapMode.READ_WRITE, 0, fc.size()).asIntBuffer();
    ib.put(0);
    for (int i = 1; i < 10; i++)
      ib.put(ib.get(i - 1));
    fc.close();
  }
}

FileChannel.MapMode.READ_ONLY

   
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String args[]) {
    FileInputStream fIn;
    FileOutputStream fOut;
    FileChannel fIChan, fOChan;
    long fSize;
    MappedByteBuffer mBuf;
    try {
      fIn = new FileInputStream(args[0]);
      fOut = new FileOutputStream(args[1]);
      fIChan = fIn.getChannel();
      fOChan = fOut.getChannel();
      fSize = fIChan.size();
      mBuf = fIChan.map(FileChannel.MapMode.READ_ONLY, 0, fSize);
      fOChan.write(mBuf); // this copies the file
      fIChan.close();
      fIn.close();
      fOChan.close();
      fOut.close();
    } catch (IOException exc) {
      System.out.println(exc);
      System.exit(1);
    } catch (ArrayIndexOutOfBoundsException exc) {
      System.out.println("Usage: Copy from to");
      System.exit(1);
    }
  }
}

FileChannel.MapMode.READ_WRITE

   
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.IntBuffer;
import java.nio.channels.FileChannel;
public class Main {
  public static void main(String[] args) throws IOException {
    FileChannel fc = new RandomAccessFile(new File("temp.tmp"), "rw").getChannel();
    IntBuffer ib = fc.map(FileChannel.MapMode.READ_WRITE, 0, fc.size()).asIntBuffer();
    ib.put(0);
    for (int i = 1; i < 10; i++)
      ib.put(ib.get(i - 1));
    fc.close();
  }
}

FileChannel: position()

 
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
public class Main {
  public static void main(String[] argv) throws IOException {
    RandomAccessFile randomAccessFile = new RandomAccessFile("test.dat", "r");
    randomAccessFile.seek(1000);
    FileChannel fileChannel = randomAccessFile.getChannel();
    // This will print "1000"
    System.out.println("file pos: " + fileChannel.position());
    randomAccessFile.seek(500);
    // This will print "500"
    System.out.println("file pos: " + fileChannel.position());
    fileChannel.position(200);
    // This will print "200"
    System.out.println("file pos: " + randomAccessFile.getFilePointer());
  }
}

FileChannel: position(long newPosition)

 
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class Main {
  private static final int BSIZE = 1024;
  public static void main(String[] args) throws Exception {
    FileChannel fc = new RandomAccessFile("data.txt", "rw").getChannel();
    fc.position(fc.size());
    fc.write(ByteBuffer.wrap("Some more".getBytes()));
    fc.close();
  }
}

FileChannel: read(ByteBuffer dst)

   
import java.io.FileInputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class Main {
  private static final int BSIZE = 1024;
  public static void main(String[] args) throws Exception {
    FileChannel fc = new FileInputStream("data.txt").getChannel();
    ByteBuffer buff = ByteBuffer.allocate(BSIZE);
    fc.read(buff);
    buff.flip();
    while (buff.hasRemaining())
      System.out.print((char) buff.get());
  }
}

FileChannel: size()

   
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String args[]) {
    FileInputStream fIn;
    FileChannel fChan;
    long fSize;
    ByteBuffer mBuf;
    try {
      fIn = new FileInputStream("test.txt");
      fChan = fIn.getChannel();
      fSize = fChan.size();
      mBuf = ByteBuffer.allocate((int) fSize);
      fChan.read(mBuf);
      mBuf.rewind();
      for (int i = 0; i < fSize; i++)
        System.out.print((char) mBuf.get());
      fChan.close();
      fIn.close();
    } catch (IOException exc) {
      System.out.println(exc);
    }
  }
}

FileChannel: transferFrom(ReadableByteChannel src, long position, long count)

 
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.channels.FileChannel;
public class Main {
  public static void main(String[] args) {
    FileChannel in = null;
    FileChannel out = null;
    if (args.length < 2) {
      System.out.println("Usage: java Copy <from> <to>");
      System.exit(1);
    }
    try {
      in = new FileInputStream(args[0]).getChannel();
      out = new FileOutputStream(args[1]).getChannel();
      out.transferFrom(in, 0L, (int) in.size());
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

FileChannel: transferTo(long position, long count, WritableByteChannel target)

   
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String[] args) throws Exception{
    String fromFileName = args[0];
    String toFileName = args[1];
    FileChannel in = new FileInputStream(fromFileName).getChannel();
    FileChannel out = new FileOutputStream(toFileName).getChannel();
    in.transferTo(0, (int) in.size(), out);
    in.close();
    out.close();
  }
}

FileChannel: tryLock()

 
import java.io.FileOutputStream;
import java.nio.channels.FileLock;
public class Main {
  public static void main(String[] args) throws Exception {
    FileOutputStream fos = new FileOutputStream("file.txt");
    FileLock fl = fos.getChannel().tryLock();
    if (fl != null) {
      System.out.println("Locked File");
      Thread.sleep(100);
      fl.release();
      System.out.println("Released Lock");
    }
    fos.close();
  }
}

FileChannel: write(ByteBuffer buffer)

   
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String args[]) {
    FileOutputStream fileOutputStream;
    FileChannel fileChannel;
    ByteBuffer byteBuffer;
    try {
      fileOutputStream = new FileOutputStream("test.txt");
      fileChannel = fileOutputStream.getChannel();
      byteBuffer = ByteBuffer.allocateDirect(26);
      for (int i = 0; i < 26; i++)
        byteBuffer.put((byte) ("A" + i));
      byteBuffer.rewind();
      fileChannel.write(byteBuffer);
      fileChannel.close();
      fileOutputStream.close();
    } catch (IOException exc) {
      System.out.println(exc);
    }
  }
}

FileChannel: write(MappedByteBuffer buffer)

   
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String args[]) {
    FileInputStream fIn;
    FileOutputStream fOut;
    FileChannel fIChan, fOChan;
    long fSize;
    MappedByteBuffer mBuf;
    try {
      fIn = new FileInputStream(args[0]);
      fOut = new FileOutputStream(args[1]);
      fIChan = fIn.getChannel();
      fOChan = fOut.getChannel();
      fSize = fIChan.size();
      mBuf = fIChan.map(FileChannel.MapMode.READ_ONLY, 0, fSize);
      fOChan.write(mBuf); // this copies the file
      fIChan.close();
      fIn.close();
      fOChan.close();
      fOut.close();
    } catch (IOException exc) {
      System.out.println(exc);
      System.exit(1);
    } catch (ArrayIndexOutOfBoundsException exc) {
      System.out.println("Usage: Copy from to");
      System.exit(1);
    }
  }
}