How to Append Content to File in Java

Appending content to a file in Java is a common task that you might encounter frequently. Whether you are logging information, writing data records, or updating files with new entries, appending ensures that new data is added without overwriting existing content. This blog post will guide you through the process of appending content to a file using various classes from the java.io package.

Table of Contents

1. Introduction
2. Creating a Sample File
3. Using FileWriter to Append Content
4. Using BufferedWriter to Append Content
5. Using PrintWriter to Append Content
6. Conclusion

Introduction

In Java, appending content to a file can be accomplished by opening the file in append mode. Several classes from the java.io package can be used to achieve this, including FileWriter, BufferedWriter, and PrintWriter. This blog post will walk you through how to use each of these classes to append content to a file.

Creating a Sample File

Before we begin appending content, let's create a sample file with some initial content. This will serve as the basis for our demonstration.

Step 1: Create a sample.txt File with Initial Content

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

public class CreateSampleFile {
    public static void main(String[] args) {
        try (FileWriter fw = new FileWriter("sample.txt")) {
            fw.write("Initial content in sample.txt\n");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Run the above code to create a sample.txt file with the initial content "Initial content in sample.txt".

Using FileWriter to Append Content

FileWriter is a class used for writing character files. To append content to a file, you need to pass a boolean value of true to its constructor.

Example: Appending Content Using FileWriter

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

public class FileWriterAppendExample {
    public static void main(String[] args) {
        try (FileWriter fw = new FileWriter("sample.txt", true)) { // 'true' for append mode
            fw.write("Appending content using FileWriter.\n");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In the above example:

• The FileWriter constructor takes a file name and a boolean value. The boolean value true indicates that the file should be opened in append mode.
• The write() method is used to append content to the file.

Run this code and check the sample.txt file to see the appended content.

Using BufferedWriter to Append Content

BufferedWriter provides buffering for Writer instances, improving performance by reducing the number of I/O operations. It can be used in conjunction with FileWriter to append content to a file.

Example: Appending Content Using BufferedWriter

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

public class BufferedWriterAppendExample {
    public static void main(String[] args) {
        try (BufferedWriter bw = new BufferedWriter(new FileWriter("sample.txt", true))) {
            bw.write("Appending content using BufferedWriter.\n");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In the above example:

• BufferedWriter is used to wrap a FileWriter instance.
• The BufferedWriter constructor takes a FileWriter object opened in append mode.
• The write() method is used to append content to the file.

Run this code and check the sample.txt file to see the appended content.

Using PrintWriter to Append Content

PrintWriter is another class that can be used for appending content to a file. It offers convenient methods for writing formatted text.

Example: Appending Content Using PrintWriter

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

public class PrintWriterAppendExample {
    public static void main(String[] args) {
        try (PrintWriter pw = new PrintWriter(new FileWriter("sample.txt", true))) {
            pw.println("Appending content using PrintWriter.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In the above example:

• PrintWriter is used to wrap a FileWriter instance.
• The FileWriter is opened in append mode.
• The println() method is used to append a line of text to the file.

Run this code and check the sample.txt file to see the appended content.

Conclusion

Appending content to a file in Java can be accomplished using several different classes, each with its own benefits. FileWriter is straightforward and easy to use, while BufferedWriter offers improved performance by reducing the number of I/O operations. PrintWriter provides convenient methods for writing formatted text.