FileChannel write

In this chapter you will learn:

How to write ByteBuffer to a FileChannel
Transfers bytes from this channel's file to the given writable byte channel

Write ByteBuffer to a FileChannel

The following code uses write(ByteBuffer buffer) to write byte array in the ByteBuffer to FileChannel.

After filling byte array to the ByteBuffer, remember to call rewind the reset the reading position for the ByteBuffer.

import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
//j  a  v  a 2  s . com
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);
    }
  }
}

The following code creates a MappedByteBuffer and map a FileChannel to it. Then it writes the MappedByteBuffer to another FileChannel.

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
//from j a  va  2  s. c  om
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);
    }
  }
}

Transfers bytes from one channel to a writable byte channel

abstract long transferTo(long position, long count, WritableByteChannel target) transfers bytes from this channel's file to the given writable byte channel.

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.channels.FileChannel;
/*j  av  a 2 s . c  om*/
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();
  }
}

Next chapter...

What you will learn in the next chapter:

Home » Java Tutorial » NIO

FileChannel write

Write ByteBuffer to a FileChannel

Transfers bytes from one channel to a writable byte channel

Next chapter...

NIO

FileChannel

FileChannel position

FileChannel lock

FileChannel read

FileChannel write