Data Transfer between Channels

In Java NIO we can directly transfer the data from one channel to another very frequently. The transfer of file data in bulk is very common that a couple of optimization methods have been added to FileChannel class for making it more efficient.

The two methods added to FileChannel class for data transfer between channels are:

FileChannel.transferTo() method
FileChannel.transferFrom() method

FileChannel.transferTo() method

The transferTo() method allows the data transfer from a FileChannel into some other channel.

Let's see the example of transferTo() method:

public abstract class Channel extends AbstractChannel
{  
public abstract long transferTo (long position, long count, WritableByteChannel target);
}

FileChannel.transferFrom() method

The transferFrom() method allows the data transfer from a source channel into the FileChannel.

Let's see the example of transferFrom() method:

public abstract class Channel extends AbstractChannel
{  
public abstract long transferFrom (ReadableByteChannel src, long position, long count);
}

Basic Channel to Channel Data Transfer Example

Let's see the simple example of reading the file contents from 4 different files and write their combined output into a fifth file:

package com.javatpoint;

import java.io.File;
import java.io.FileOutputStream;
import java.io.FileInputStream;
import java.nio.channels.WritableByteChannel;
import java.nio.channels.FileChannel;
public class Transfer
{
    public static void main(String[] argv) throws Exception 
    {
        //Path of Input files
       String[] iF = new String[]{"D:\\input1.txt","D:\\input2.txt","D:\\input3.txt","D:\\input4.txt"};
        //Path of Output file and contents will be written in this file
        String oF = "D:\\combine_output.txt";
         //Acquired the channel for output file
        FileOutputStream output = new FileOutputStream(new File(oF));
        WritableByteChannel targetChannel = output.getChannel();
          for (int j = 0; j < iF.length; j++)
        {
            //Get the channel for input files
            FileInputStream input = new FileInputStream(iF[j]);
            FileChannel inputChannel = input.getChannel();
 
            //The data is tranfer from input channel to output channel
            inputChannel.transferTo(0, inputChannel.size(), targetChannel);
 
            //close an input channel
            inputChannel.close();
            input.close();
        }
        //close the target channel
        targetChannel.close();
        output.close();
    }
}

Output:

In above program the content of 4 different files i.e. input1.txt, input2.txt, input3.txt and input4.txt is read and write their combined output into a fifth file i.e. combine_output.txt.

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