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How to use RandomAccessFile class?

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 / 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 com.javacoderanch.example.io;

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

public class RandomAccessFileExample {

    public static void main(String[] args) {
        try {
            //
            // 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 opeartion to the RandomAccessFile
            // instance.
            //
            RandomAccessFile raf = new RandomAccessFile("books.dat", "rw");

            //
            // 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";

            for (int i = 0; i < books.length; i++) {
                raf.writeUTF(books[i]);
            }

            //
            // 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 (FileNotFoundException e) {
            e.printStackTrace();
        } 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