How to Append Data to the End of Existing File in Java?

It's often useful to be able to append data to an existing file rather than overwriting it.

The BufferedWriter writes text to a character-output stream, buffering characters so as to provide for the efficient writing of single characters, arrays, and strings.The FileWriter is a convenience class used for writing character files. The constructors of this class assume that the default character encoding and the default byte-buffer size are acceptable. Also, theFileWriter supports to append data to existing file. For example,

class FileAppending 
{
    public static void main(String args[]) {
        try{
            FileWriter fstream = new FileWriter("x.txt",true);
            BufferedWriter fbw = new BufferedWriter(fstream);
            fbw.write("append txt...");
            fbw.newLine();
            fbw.close();
        }catch (Exception e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

The FileWriter uses your computer's default character encoding. For UTF-8 file, you may use OutputStreamWriter with FileOutputStream class. The FileOutputStream(String fname, boolean append) constructor creates an output file stream to write to the file with the specified name. If the second argument is true, then bytes will be written to the end of the file rather than the beginning. The OutputStreamWriter class connects byte streams and character streams. The OutputStreamWriter writes bytes onto the underlying output stream after translating characters according to a specified character encoding such as UTF-8. For example,

class FileAppending 
{
    public static void main(String args[]) {
        try{
        
            OutputStreamWriter writer = new OutputStreamWriter(
                  new FileOutputStream("x.txt", true), "UTF-8");
            BufferedWriter fbw = new BufferedWriter(writer);
            fbw.write("append txt...");
            fbw.newLine();
            fbw.close();
        }catch (Exception e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}