Java - RandomAccessFile getChannel() method

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Description

The Java RandomAccessFile getChannel() method returns the unique FileChannel object associated with this file.

getChannel() method −

• Returns the FileChannel object associated with the RandomAccessFile.

• The FileChannel can be used for advanced file I/O operations like memory-mapped files, locking, reading/writing via buffers, and more.

• You can use it for both reading and writing, depending on the mode ("r" or "rw").

Declaration

Following is the declaration for java.io.RandomAccessFile.getChannel() method.

public final FileChannel getChannel()

Parameters

NA

Return Value

This method returns the file channel associated with this file.

Exception

NA

Example - Usage of RandomAccessFile getChannel() method

The following example shows the usage of RandomAccessFile getChannel() method.

RandomAccessFileDemo.java

package com.tutorialspoint;

import java.io.IOException;
import java.io.RandomAccessFile;

public class RandomAccessFileDemo {
   public static void main(String[] args) {

      try {
         // create a new RandomAccessFile with filename test
         RandomAccessFile raf = new RandomAccessFile("test.txt", "rw");

         // write something in the file
         raf.writeUTF("Hello World");

         // set the file pointer at 0 position
         raf.seek(0);

         // read and print the contents of the file
         System.out.println("" + raf.readUTF());

         // return the channel of the file
         System.out.println("" + raf.getChannel());

         // close the strea and release resources
         raf.close();
      } catch (IOException ex) {
         ex.printStackTrace();
      }
   }
}

Output

Assuming we have a text file test.txt in current directory which has the following content. This file will be used as an input for our example program −

ABCDE

Let us compile and run the above program, this will produce the following result −

Hello World
sun.nio.ch.FileChannelImpl@3d4b7453

Example - Getting the size of the file using getChannel()

The following example shows the usage of RandomAccessFile getChannel() method.

RandomAccessFileDemo.java

package com.tutorialspoint;

import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.io.IOException;

public class RandomAccessFileDemo {
   public static void main(String[] args) {
      try (RandomAccessFile raf = new RandomAccessFile("example1.txt", "rw")) {
         raf.writeUTF("Hello, FileChannel!");

         FileChannel channel = raf.getChannel();
         long size = channel.size();  // Get the size of the file

         System.out.println("Size of file (in bytes): " + size);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Size of file (in bytes): 24

Explanation

• RandomAccessFile writes a UTF string to a file.

• getChannel() returns the FileChannel associated with it.

• The channel is used to get the file size using channel.size().

Example - Positioning the file pointer using FileChannel.position()

The following example shows the usage of RandomAccessFile getChannel() method.

RandomAccessFileDemo.java

package com.tutorialspoint;

import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.io.IOException;
import java.nio.ByteBuffer;

public class RandomAccessFileDemo {
   public static void main(String[] args) {
      try (RandomAccessFile raf = new RandomAccessFile("example2.txt", "rw")) {
         raf.writeUTF("1234567890");

         FileChannel channel = raf.getChannel();
         channel.position(2); // Move to 2nd byte (inside UTF string)

         ByteBuffer buffer = ByteBuffer.allocate(8);
         int bytesRead = channel.read(buffer);  // Read 8 bytes from position 2
         buffer.flip();

         System.out.print("Data read from position 2: ");
         while (buffer.hasRemaining()) {
            System.out.print((char) buffer.get());
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Data read from position 2: 12345678

Explanation

• Writes data using RandomAccessFile.

• Uses the FileChannel to move the file pointer to a specific position and read from there using a ByteBuffer.

• Demonstrates how to perform non-sequential (random) file access with getChannel().