Module# 12: Java IO Streams and File Lecture#46: Random Access File

// Example 46.1: Reading from a RAF

import java.io.IOException;

import java.io.RandomAccessFile;

public class RandomAccessFileExample {

static final String FILEPATH ="NPTEL.txt";

public static void main(String[] args) {

try {

System.out.println(new String(readFromFile(FILEPATH, 0, 18)));

} 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;

}

}

// Example 46.2: Writing into a RAF

import java.io.IOException;

import java.io.RandomAccessFile;

public class RandomAccessFileExample {

static final String FILEPATH ="myFile.TXT";

public static void main(String[] args) {

try {

writeToFile(FILEPATH, "Data Structures and Algorithms Using Java", 41);

} catch (IOException e) {

e.printStackTrace();

}

}

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();

}

}

// Example 46.3: Reading and writing RAF

import java.io.*;

class RandomIO{

public static void main (String args[)){

RandomAccessFile file = null;

try {

file = new

RandomAccessFile("rand.dat","rw");

// Writing to the file

file.writeChar('X');

file.writelnt(555);

file.writeDouble(3.1412);

file.seek (0);

// Go to the beginning

// Reading from the file

System.out.println(file.readChar());

// Continued on...

System.out.println(file.readlnt());

System.out.println(file.readDouble());

file.seek(2); // Go to the second item

System.out.println(file.readlnt());

// Go to the end and append false to the file

file.seek(file.length());

file.writeBoolean(false);

file. seek (4) ;

System.out.println(file.readBoolean());

file.close();

}

catch(IOException e)

{

System.out.println(e);

}

}

}

// Example 46.4: Appending to a RAF

import java.io.*;

class RandomAccess {

static public void main(String args[]){

RandomAccessFile rFile;

try{

rFile = new RandomAccessFile("city.txt","rw");

rFile.seek(rFile.lenght()); // Go to the end

rFile.writeByte(“Joy with Java\n"); //Append MUMBAI

rFile.close();

}

catch(IOException ioe){

System.out.println(ioe);

}

}

}

// Example 46.5: Reading and writing objects (Defining objects)

/* This program consists of three parts:

a) Define and creating objects

b) Writing objects into a file

c) Redaig objects from the file

In the following, the class files for each of ythe above parts are given. */

// Defining objects

import java.io.Serializable;

import java.util.*;

public class Student implements Serializable {

//default serialVersion id

private static final long serialVersionUID = 1L;

private String firstName;

private String lasName;

private int age;

private int marks[] = new int[5];

public Student(String fname, String lname, int age, int smarks[]){

this.firstName = fname;

this.lastName = lname;

this.age = age;

this.marks = smarks;

}

public void setFirstName(String fname) {

this.firstName = fname;

}

public String getFirstName() {

return this.firstName;

}

public void setLastName(String lname) {

this.firstName = lname;

}

public String getLastName() {

return this.lastName;

}

public void setAge(int age) {

this.age = age;

}

public int getAge() {

return this.age;

}

public void setMarks(int smarks[]) {

this.marks = smarks;

}

public int[] getMarks() {

return this.marks;

}

@Override

public String toString() {

return new StringBuffer(" \nFirst Name: ").append(this.first_name)

.append(" \nLast Name : ").append(this.last_name)

.append(" \nAge : ").append(this.age)

.append(" \nMarks : ")

.append(Arrays.toString(this.marks)).toString();

}

}

// Create objects and writing into file

import java.io.FileOutputStream;

import java.io.ObjectOutputStream;

public class WriteObjectDemo {

private static final String filepath="D:\\Java\\obj";

public static void main(String args[]) {

WriteObject objectIO = new ObjectIO();

int m[] = {50,47,89,65,78};

Student student = new Student("John","Frost",22,m);

objectIO.writeObjectToFile(student);

}

public void writeObjectToFile(Object serObj) {

try {

FileOutputStream fileOut = new FileOutputStream(filepath);

ObjectOutputStream objectOut = new ObjectOutputStream(fileOut);

objectOut.writeObject(serObj);

objectOut.close();

System.out.println("The Object is successfully written to a file");

} catch (Exception ex) {

ex.printStackTrace();

}

}

}

// Reading objects from file

import java.io.FileInputStream;

import java.io.ObjectInputStream;

public class ReadObjectDemo{

private static final String filepath="D:\\Java\\obj";

public static void main(String args[]) {

ReadObject objectIO = new ReadObject();

objectIO.readObjectFromFile();

}

public void readObjectFromFile() {

try {

FileInputStream fileIn = new FileInputStream(filepath);

ObjectInputStream objectIn = new ObjectInputStream(fileIn);

Student student = (Student) objectIn.readObject();

System.out.println(student.toString());

objectIn.close();

System.out.println("The Object was succesfully read from the file");

} catch (Exception ex) {

ex.printStackTrace();

}

}

}