How do I Java append to file when I need to repeatedly add text to an existing file?

General Discussions
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1

How do I Java append to file when I need to repeatedly add text to an existing file?

I want to ensure that each new piece of text is added without overwriting the existing content. What’s the best way to achieve this in Java?

2

From my experience, the best way to java append to file is by using FileWriter with the append mode enabled. It’s simple, and you don’t have to worry about overwriting the existing content. Here’s a quick example:

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

public class AppendToFile {
    public static void main(String[] args) {
        try (FileWriter writer = new FileWriter("output.txt", true)) { // 'true' enables append mode
            writer.write("Appending this line to the file.\n");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

This ensures that every new line gets added to the file rather than replacing what’s already there.

3

That’s a solid approach, But just to build on that — if you’re dealing with frequent file writes, you might want to consider using a BufferedWriter for better performance. This reduces the number of I/O operations because it buffers data before writing it to the file. It makes a noticeable difference when you’re working with large files or frequent appends. Here’s a quick revision of the code you shared:

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

public class AppendToFileBuffered {
    public static void main(String[] args) {
        try (BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt", true))) {
            writer.write("Appending efficiently with BufferedWriter.\n");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Buffered writing is more efficient because it minimizes disk access, which is especially useful for applications with repeated java append to file operations."

4

Great suggestions, both of you! Now, if you’re looking for a more modern and thread-safe approach, I’d recommend using java NIO for appending to a file. NIO is perfect for multi-threaded environments, and it’s both efficient and concise. With NIO, you can append data to a file without the extra overhead that comes with older methods. Check this out:

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.Collections;

public class AppendToFileNIO {
    public static void main(String[] args) {
        try {
            Files.write(Paths.get("output.txt"),
                        Collections.singletonList("Appending with NIO!\n"),
                        StandardOpenOption.CREATE, StandardOpenOption.APPEND);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

The beauty of this method is:

  • Thread-safe: Ideal for multi-threaded applications.
  • Concise: Less boilerplate code compared to using FileWriter or BufferedWriter.
  • Efficient with large files: Directly interacts with the Path and Files API.

If you’re working in a more modern Java environment, java append to file with NIO is a fantastic choice!"