File Handling in Java with CRUD operations

So far the operations using Java programs are done on a prompt/terminal which is not stored anywhere. But in the software industry, most of the programs are written to store the information fetched from the program. One such way is to store the fetched information in a file. A file is a container which is used to store various types of information. Data is permanently stored in secondary memory by creating a file with a unique name. A file may consist of text, image or any other document.

Different operations that can be performed on a file are:

  1. Creation of a new file
  2. Opening an existing file
  3. Reading from file
  4. Writing to a file
  5. Moving to a specific location in a file
  6. Closing a file

Different classes that can be used in Java for File Handling:



  1. InputStream
  2. OutputStream
  3. FilterOutputStream
  4. FileOutputStream
  5. ByteArrayOutputStream
  6. ByteArrayInputStream
  7. FileInputStream
  8. FilterInputStream
  9. StringBufferInputStream
  10. SequenceInputStream
  11. BufferedOutputStream
  12. StringBufferInputStream
  13. DataOutputStream
  14. PrintStream
  15. BufferedInputStream
  16. DataInputStream
  17. PushbackInputStream

In this article, we will learn how Java ByteStreams are used to perform input and output of 8-bits(1 byte) using class RandomAccessFile which consists method writeBytes() and readBytes() to write and read the data in the form of bytes.

Various Methods used to perfrom File operation:

  • writeBytes(String s): Writes the string to the file as a sequence of bytes.
  • readLine(): Reads the next line of text from this file.
  • getFilePointer(): Returns the current offset in this file.
  • length(): Returns the length of this file and return type is long.
  • close(): Closes this random access file stream and releases any system resources associated with the stream.
  • setLength(long newLength): Sets the length of this file.
  • seek(long pos): Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs.

File opening modes in Java:

Value Meaning
“r” Open for reading only. Invoking any of the write methods of the resulting object will cause an IOException to be thrown.
“rw” Open for reading and writing. If the file does not already exist then an attempt will be made to create it.
“rws” Open for reading and writing, as with “rw”, and also require that every update to the file’s content or metadata be written synchronously to the underlying storage device.
“rwd” Open for reading and writing, as with “rw”, and also require that every update to the file’s content be written synchronously to the underlying storage device.

Syntax of Opening File using RandomAccessFile:

File file = new File( filename )
RandomAccessFile raf = new RandomAccessFile(file, mode)

CRUD operations using File Handling in Java

Example: Consider that you want to keep records of your friend’s contact number in a file. To distinguish between your friend’s name and contact number you need a separator. To do so you need to select a separator such as ‘!’ or ‘$’ or some special symbol which does not appear in your friend’s name. Then we will form a string consist of name, special symbol and number to insert into the file.

Syntax of a Contact in the file friendsContact.txt:

Name!Number

Create

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// Java program to create a file "friendsContact.txt"
// and add a new contact in the file
  
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.lang.NumberFormatException;
  
class AddFriend {
  
    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();
  
                // finding the position of '!'
                index = nameNumberString.indexOf('!');
  
                // separating name and number.
                name = nameNumberString
                           .substring(0, index);
                number
                    = Long
                          .parseLong(
                              nameNumberString
                                  .substring(index + 1));
  
                // if condition to find existence of record.
                if (name == newName || number == newNumber) {
                    found = true;
                    break;
                }
            }
  
            if (found == false) {
  
                // Enter the if block when a record
                // is not already present in the file.
                nameNumberString
                    = newName
                      + "!"
                      + String.valueOf(newNumber);
  
                // writeBytes function to write a string
                // as a sequence of bytes.
                raf.writeBytes(nameNumberString);
  
                // To insert the next record in new line.
                raf.writeBytes(System.lineSeparator());
  
                // Print the message
                System.out.println(" Friend added. ");
  
                // Closing the resources.
                raf.close();
            }
            // 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);
        }
    }
}

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Read

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// Java program to read from file "friendsContact.txt"
// and display the contacts
  
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.lang.NumberFormatException;
  
class DisplayFriends {
  
    public static void main(String data[])
    {
  
        try {
  
            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;
  
            // Traversing the file
            // getFilePointer() give the current offset
            // value from start of the file.
            while (raf.getFilePointer() < raf.length()) {
  
                // reading line from the file.
                nameNumberString = raf.readLine();
  
                // finding the position of '!'
                index = nameNumberString.indexOf('!');
  
                // separating name and number.
                name = nameNumberString
                           .substring(0, index);
                number
                    = Long
                          .parseLong(
                              nameNumberString
                                  .substring(index + 1));
  
                // Print the contact data
                System.out.println("Friend Name: "
                                   + name + "\n"
                                   + "Contact Number: "
                                   + number + "\n");
            }
  
            catch (IOException ioe)
            {
  
                System.out.println(ioe);
            }
            catch (NumberFormatException nef)
            {
  
                System.out.println(nef);
            }
        }
    }

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Update

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// 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();
  
                // finding the position of '!'
                index = nameNumberString.indexOf('!');
  
                // separating name and number.
                name = nameNumberString
                           .substring(0, index);
                number = Long
                             .parseLong(nameNumberString
                                            .substring(index + 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);
        }
    }
}

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Delete

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// 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();
  
                // finding the position of '!'
                index = nameNumberString.indexOf('!');
  
                // separating name and number.
                name = nameNumberString
                           .substring(0, index);
                number
                    = Long
                          .parseLong(
                              nameNumberString
                                  .substring(index + 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);
        }
    }
}

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Output:

  • Create operation:
    Compiling and Adding the contact in the newly created file:



    javac AddFriend.java 
    
    java AddFriend abc 1111111111 
    Friend added
    
    java AddFriend pqr 1111111111
    Input name or number already exist
    

    File:

  • Read Operation:
    Compiling and reading the contacts from the file:

    javac DisplayFriends.java 
    
    java DisplayFriends
    Friend Name: abc 
    Contact Number: 1234567890
    
    Friend Name: lmn
    Contact Number: 3333333333
    
    Friend Name: xyz 
    Contact Number: 4444444444
    

    File:

  • Update Operation:
    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.
    

    File:

  • Delete Operation:
    Compiling and deleting the contact in the file:

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

    File:



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