How to Append Content to File in Java

Overview

In Java, you can use FileWriter(file,true) to append new content to the end of a file.

1. All existing content will be overridden.

new FileWriter(file);

2. Keep the existing content and append the new content to the end of a file.

new FileWriter(file,true);

FileWriter – Append file example

1. Let's create a file "sample.txt" under directory "C:/workspace".
2. Keep some content in file C:/workspace/sample.txt like

There is some content in file

3. Let's Java example to append new content to the end of a file.

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

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * This Java program demonstrates how to append content to existing file contents.
 * @author javaguides.net
 */

public class AppendFileExample {
	
	private static final Logger LOGGER = LoggerFactory
			.getLogger(AppendFileExample.class);
	
	public static void main(String[] args) {
		appendToExitingFile();
	}
	
	public static void appendToExitingFile(){
		try (Writer writer = new FileWriter("C:/workspace/sample.txt",true);
				BufferedWriter bw = new BufferedWriter(writer)) {
			String content = "append something to existing file\n";
			bw.write(content);
		} catch (IOException e) {
			LOGGER.error(e.getMessage());
		}
	}
}

Output: Let's open the "sample.txt" and verify the content.

There is some content in file append something to existing file

Reference https://docs.oracle.com/javase/8/docs/api/java/io/FileWriter.html https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

Tips

User Writer interface as reference type so it provides loose coupling. In future we may use some other Writer classes.