This is an example of using RandomAccessFile class to read and write data to a file. Using RandomAccessFile enable us to read or write to a specific location in the file at the file pointer. Imagine the file as a large array of data that have their own index.

In the code below you’ll see how to create an instance of RandomAccessFile and define its operation mode (read or write). After we create an object we write some data, some book’s titles to the file. The last few line of the codes demonstrate how to read file data.

package org.kodejava.io;

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

public class RandomAccessFileExample {

    public static void main(String[] args) {
        try {
            // Let's write some book's title to the end of the file
            String[] books = new String[5];
            books[0] = "Professional JSP";
            books[1] = "The Java Application Programming Interface";
            books[2] = "Java Security";
            books[3] = "Java Security Handbook";
            books[4] = "Hacking Exposed J2EE & Java";

            // Create a new instance of RandomAccessFile class. We'll do a "r"
            // read and "w" write operation to the file. If you want to do a write
            // operation you must also allow read operation to the RandomAccessFile
            // instance.
            RandomAccessFile raf = new RandomAccessFile("books.dat", "rw");
            for (String book : books) {
                raf.writeUTF(book);
            }

            // Write another data at the end of the file.
            raf.seek(raf.length());
            raf.writeUTF("Servlet & JSP Programming");

            // Move the file pointer to the beginning of the file
            raf.seek(0);

            // While the file pointer is less than the file length, read the
            // next strings of data file from the current position of the
            // file pointer.
            while (raf.getFilePointer() < raf.length()) {
                System.out.println(raf.readUTF());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

The result of our program are:

Professional JSP
The Java Application Programming Interface
Java Security
Java Security Handbook
Hacking Exposed J2EE & Java
Servlet & JSP Programming