File Handling in Java with CRUD operations - 2

Software Development
#1

How to Update a File in Java?

  • Java

// Java program to update in the file "friendsContact.txt"

// and change the number of an old contact

import java.io.File;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.lang.NumberFormatException;

class UpdateFriend {

public static void main(String data[])

{

try {

// Get the name of the contact to be updated

// from the Command line argument

String newName = data[ 0 ];

// Get the number to be updated

// from the Command line argument

long newNumber = Long.parseLong(data[ 1 ]);

String nameNumberString;

String name;

long number;

int index;

// Using file pointer creating the file.

File file = new File( "friendsContact.txt" );

if (!file.exists()) {

// Create a new file if not exists.

file.createNewFile();

}

// Opening file in reading and write mode.

RandomAccessFile raf

= new RandomAccessFile(file, "rw" );

boolean found = false ;

// Checking whether the name

// of contact already exists.

// getFilePointer() give the current offset

// value from start of the file.

while (raf.getFilePointer() < raf.length()) {

// reading line from the file.

nameNumberString = raf.readLine();

// splitting the string to get name and

// number

String[] lineSplit

= nameNumberString.split( "!" );

// separating name and number.

name = lineSplit[ 0 ];

number = Long.parseLong(lineSplit[ 1 ]);

// if condition to find existence of record.

if (name == newName

|| number == newNumber) {

found = true ;

break ;

}

}

// Update the contact if record exists.

if (found == true ) {

// Creating a temporary file

// with file pointer as tmpFile.

File tmpFile = new File( "temp.txt" );

// Opening this temporary file

// in ReadWrite Mode

RandomAccessFile tmpraf

= new RandomAccessFile(tmpFile, "rw" );

// Set file pointer to start

raf.seek( 0 );

// Traversing the friendsContact.txt file

while (raf.getFilePointer()

< raf.length()) {

// Reading the contact from the file

nameNumberString = raf.readLine();

index = nameNumberString.indexOf( '!' );

name = nameNumberString.substring(

0 , index);

// Check if the fetched contact

// is the one to be updated

if (name.equals(inputName)) {

// Update the number of this contact

nameNumberString

= name + "!"

+ String.valueOf(newNumber);

}

// Add this contact in the temporary

// file

tmpraf.writeBytes(nameNumberString);

// Add the line separator in the

// temporary file

tmpraf.writeBytes(

System.lineSeparator());

}

// The contact has been updated now

// So copy the updated content from

// the temporary file to original file.

// Set both files pointers to start

raf.seek( 0 );

tmpraf.seek( 0 );

// Copy the contents from

// the temporary file to original file.

while (tmpraf.getFilePointer()

< tmpraf.length()) {

raf.writeBytes(tmpraf.readLine());

raf.writeBytes(System.lineSeparator());

}

// Set the length of the original file

// to that of temporary.

raf.setLength(tmpraf.length());

// Closing the resources.

tmpraf.close();

raf.close();

// Deleting the temporary file

tmpFile.delete();

System.out.println( " Friend updated. " );

}

// The contact to be updated

// could not be found

else {

// Closing the resources.

raf.close();

// Print the message

System.out.println( " Input name"

+ " does not exists. " );

}

}

catch (IOException ioe) {

System.out.println(ioe);

}

catch (NumberFormatException nef) {

System.out.println(nef);

}

}

}

Output:

Compiling and updating the contact in the file:

javac UpdateFriend.java java UpdateFriend abc 1234567890 Friend updated. java UpdateFriend tqr Input name does not exists.

How to Delete a File in Java?

  • Java

// Java program to delete a contact

// from the file "friendsContact.txt"

import java.io.File;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.lang.NumberFormatException;

class DeleteFriend {

public static void main(String data[])

{

try {

// Get the name of the contact to be updated

// from the Command line argument

String newName = data[ 0 ];

String nameNumberString;

String name;

long number;

int index;

// Using file pointer creating the file.

File file = new File( "friendsContact.txt" );

if (!file.exists()) {

// Create a new file if not exists.

file.createNewFile();

}

// Opening file in reading and write mode.

RandomAccessFile raf

= new RandomAccessFile(file, "rw" );

boolean found = false ;

// Checking whether the name of contact exists.

// getFilePointer() give the current offset

// value from start of the file.

while (raf.getFilePointer() < raf.length()) {

// reading line from the file.

nameNumberString = raf.readLine();

// splitting the string to get name and

// number

String[] lineSplit

= nameNumberString.split( "!" );

// separating name and number.

name = lineSplit[ 0 ];

number = Long.parseLong(lineSplit[ 1 ]);

// if condition to find existence of record.

if (name == newName) {

found = true ;

break ;

}

}

// Delete the contact if record exists.

if (found == true ) {

// Creating a temporary file

// with file pointer as tmpFile.

File tmpFile = new File( "temp.txt" );

// Opening this temporary file

// in ReadWrite Mode

RandomAccessFile tmpraf

= new RandomAccessFile(tmpFile, "rw" );

// Set file pointer to start

raf.seek( 0 );

// Traversing the friendsContact.txt file

while (raf.getFilePointer()

< raf.length()) {

// Reading the contact from the file

nameNumberString = raf.readLine();

index = nameNumberString.indexOf( '!' );

name = nameNumberString.substring(

0 , index);

// Check if the fetched contact

// is the one to be deleted

if (name.equals(inputName)) {

// Skip inserting this contact

// into the temporary file

continue ;

}

// Add this contact in the temporary

// file

tmpraf.writeBytes(nameNumberString);

// Add the line separator in the

// temporary file

tmpraf.writeBytes(

System.lineSeparator());

}

// The contact has been deleted now

// So copy the updated content from

// the temporary file to original file.

// Set both files pointers to start

raf.seek( 0 );

tmpraf.seek( 0 );

// Copy the contents from

// the temporary file to original file.

while (tmpraf.getFilePointer()

< tmpraf.length()) {

raf.writeBytes(tmpraf.readLine());

raf.writeBytes(System.lineSeparator());

}

// Set the length of the original file

// to that of temporary.

raf.setLength(tmpraf.length());

// Closing the resources.

tmpraf.close();

raf.close();

// Deleting the temporary file

tmpFile.delete();

System.out.println( " Friend deleted. " );

}

// The contact to be deleted

// could not be found

else {

// Closing the resources.

raf.close();

// Print the message

System.out.println( " Input name"

+ " does not exists. " );

}

}

catch (IOException ioe) {

System.out.println(ioe);

}

}

}

Output:

Compiling and deleting the contact in the file:

javac DeleteFriend.java java DeleteFriend pqr Friend deleted. java DeleteFriend tqr Input name does not exists.