Java Lesson 44 – File Handling | Dataplexa

File Handling

Almost every real-world application needs to work with files — reading configuration, saving logs, storing reports, or exporting data.

File Handling in Java allows programs to create, read, write, and manage files efficiently using built-in APIs.

Why File Handling Is Important

Files allow data to persist even after a program stops running. Without file handling, all data would be lost when the application closes.

Common use cases include:

Saving user data
Reading configuration files
Generating reports
Application logging

File Class Overview

The File class (from java.io) represents a file or directory path. It does not read or write data directly, but helps manage file information.


import java.io.File;

public class Main {
    public static void main(String[] args) {

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

        System.out.println(file.exists());
        System.out.println(file.getName());
        System.out.println(file.getAbsolutePath());
    }
}

Creating a File

You can create a new file using the createNewFile() method.


import java.io.File;
import java.io.IOException;

public class Main {
    public static void main(String[] args) throws IOException {

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

        if (file.createNewFile()) {
            System.out.println("File created");
        } else {
            System.out.println("File already exists");
        }
    }
}

Writing Data to a File

Java provides classes like FileWriter and BufferedWriter to write data into files.


import java.io.FileWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) throws IOException {

        FileWriter writer = new FileWriter("example.txt");
        writer.write("Welcome to Java File Handling");
        writer.close();

        System.out.println("Data written to file");
    }
}

Reading Data from a File

To read file content, Java provides classes like FileReader and BufferedReader.


import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Main {
    public static void main(String[] args) throws IOException {

        BufferedReader reader = new BufferedReader(
                new FileReader("example.txt"));

        String line;
        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }

        reader.close();
    }
}

Appending Data to a File

You can append data instead of overwriting existing content.


FileWriter writer = new FileWriter("example.txt", true);
writer.write("\nNew line added");
writer.close();

Real-World Example

Consider an application that logs user activity.


FileWriter log = new FileWriter("app.log", true);
log.write("User logged in at " + System.currentTimeMillis() + "\n");
log.close();

Such logging is common in backend systems.

Handling File Exceptions

File operations can fail due to missing files or permission issues. Always handle exceptions properly.


try {
    FileReader reader = new FileReader("missing.txt");
} catch (IOException e) {
    System.out.println("File not found or access denied");
}

Best Practices

Always close file resources
Use buffered streams for better performance
Handle exceptions carefully
Avoid hard-coded file paths

Key Takeaways

File handling enables data persistence
Java provides rich file APIs
Essential for real-world applications

In the next lesson, we will learn about JDBC Basics and how Java connects to databases.

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