Byron Kiourtzoglou

About Byron Kiourtzoglou

Byron is a master software engineer working in the IT and Telecom domains. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.

Java RandomAccessFile Example

In this tutorial we are going to see how use RandomAccessFile in order to to read an write data to a File in random positions. The RandomAccessFile class treats the file as an array of Bytes. And you can write your data in any position of the Array. To do that, it uses a pointer that holds the current position (you can think of that pointer like a cursor in a text editor…).

RandomAccessFile does that using :

  • getFilePointer() to get the current position of the pointer
  • seek(int )to set the position of the pointer
  • read(byte[] b) to reads up to b.length bytes of data from the file into an array of bytes
  • write(byte[] b) to write b.length bytes from the specified byte array to the file, starting at the current file pointer

Take a look at the code :

package com.javacodegeeks.java.core;

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

public class RandomAccessFileEx {

	static final String FILEPATH = "C:/Users/nikos7/Desktop/input.txt";

	public static void main(String[] args) {

		try {

			System.out.println(new String(readFromFile(FILEPATH, 150, 23)));

			writeToFile(FILEPATH, "JavaCodeGeeks Rocks!", 22);
		} catch (IOException e) {
			e.printStackTrace();
		}

	}

	private static byte[] readFromFile(String filePath, int position, int size)
			throws IOException {

		RandomAccessFile file = new RandomAccessFile(filePath, "r");
		file.seek(position);
		byte[] bytes = new byte[size];
		file.read(bytes);
		file.close();
		return bytes;

	}

	private static void writeToFile(String filePath, String data, int position)
			throws IOException {

		RandomAccessFile file = new RandomAccessFile(filePath, "rw");
		file.seek(position);
		file.write(data.getBytes());
		file.close();

	}
}

 
This was en example of Java RandomAccessFile.

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