FileWriter Class

The FileWriter class in Java is used to write character-based data to files.

It is part of the java.io package and provides methods to write text data to files.

FileWriter is particularly useful when you need to create or update a text file with custom content.

In this tutorial, we will cover:

1. Basic Usage of FileWriter
2. Appending Data to an Existing File
3. Writing Characters and Strings
4. Using BufferedWriter with FileWriter
5. Handling Exceptions and Closing FileWriter

Let’s go through each section with examples.

1. Basic Usage of FileWriter

The FileWriter class has constructors to create a new file or to open an existing file for writing.

If the file does not exist, it creates it; if it does exist, it overwrites the file unless set otherwise.

Example 1: Writing a Simple Message to a File

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

public class BasicFileWriterExample {
    public static void main(String[] args) {
        try {
            // Create a FileWriter instance to write to "example.txt"
            FileWriter writer = new FileWriter("example.txt");
            
            // Write a simple message
            writer.write("Hello, World!");
            
            // Close the FileWriter
            writer.close();
            System.out.println("Successfully wrote to the file.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

• Explanation: This example creates a new file named example.txt (if it doesn’t exist) and writes the message “Hello, World!” into it. After writing, it closes the FileWriter to release resources.

2. Appending Data to an Existing File

By default, FileWriter overwrites the file.

However, you can append to an existing file by using the FileWriter constructor with true as the second parameter.

Example 2: Appending Text to a File

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

public class AppendFileWriterExample {
    public static void main(String[] args) {
        try {
            // Create a FileWriter in append mode
            FileWriter writer = new FileWriter("example.txt", true);
            
            // Append a message to the file
            writer.write("\nThis is an appended line.");
            
            // Close the FileWriter
            writer.close();
            System.out.println("Successfully appended to the file.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

• Explanation: Here, true in new FileWriter(“example.txt”, true) opens the file in append mode, so it adds new content instead of overwriting the file.

3. Writing Characters and Strings

You can write individual characters, arrays of characters, or entire strings to a file using FileWriter.

Example 3: Writing Individual Characters

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

public class WriteCharactersExample {
    public static void main(String[] args) {
        try {
            FileWriter writer = new FileWriter("characters.txt");

            // Writing individual characters
            writer.write('H');
            writer.write('e');
            writer.write('l');
            writer.write('l');
            writer.write('o');

            writer.close();
            System.out.println("Successfully wrote characters to the file.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Example 4: Writing an Array of Characters

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

public class WriteCharArrayExample {
    public static void main(String[] args) {
        try {
            FileWriter writer = new FileWriter("charArray.txt");

            // Write an array of characters
            char[] message = {'H', 'e', 'l', 'l', 'o', ' ', 'J', 'a', 'v', 'a'};
            writer.write(message);

            writer.close();
            System.out.println("Successfully wrote a character array to the file.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Example 5: Writing an Entire String

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

public class WriteStringExample {
    public static void main(String[] args) {
        try {
            FileWriter writer = new FileWriter("string.txt");

            // Write a full string
            writer.write("This is a string being written to the file!");

            writer.close();
            System.out.println("Successfully wrote a string to the file.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

4. Using BufferedWriter with FileWriter

For efficient writing, especially for large files, use BufferedWriter along with FileWriter.

BufferedWriter buffers the data, reducing the number of write operations to the disk.

Example 6: Using BufferedWriter for Buffered Writing

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

public class BufferedWriterExample {
    public static void main(String[] args) {
        try {
            // Create FileWriter and BufferedWriter
            FileWriter writer = new FileWriter("buffered.txt");
            BufferedWriter bufferedWriter = new BufferedWriter(writer);

            // Write multiple lines
            bufferedWriter.write("First line of text");
            bufferedWriter.newLine();  // Add a new line
            bufferedWriter.write("Second line of text");
            bufferedWriter.newLine();
            bufferedWriter.write("Third line of text");

            // Close the BufferedWriter and FileWriter
            bufferedWriter.close();
            writer.close();
            System.out.println("Successfully wrote to the file using BufferedWriter.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

• Explanation: BufferedWriter buffers the output, minimizing I/O operations. Here, newLine() is used to add line breaks between lines.

5. Handling Exceptions and Closing FileWriter

Always close the FileWriter after writing to release system resources.

It’s recommended to use a try-with-resources statement to automatically close the FileWriter, which avoids potential memory leaks.

Example 7: Writing to a File with try-with-resources

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

public class TryWithResourcesExample {
    public static void main(String[] args) {
        // Use try-with-resources to auto-close FileWriter
        try (FileWriter writer = new FileWriter("resources.txt")) {
            writer.write("This file is written using try-with-resources.");
            System.out.println("Successfully wrote to the file with try-with-resources.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

• Explanation: The try-with-resources statement automatically closes FileWriter at the end of the try block, eliminating the need for a separate close() call.

Summary of Key FileWriter Concepts

Conclusion

In this tutorial, we explored various ways to use the FileWriter class in Java, including:

• Basic file writing operations.
• Appending content to an existing file.
• Writing individual characters, arrays, and entire strings.
• Buffered writing with BufferedWriter for enhanced performance.
• Exception handling and safe closure using try-with-resources.