Appending one text file to another in Java

Question

Good evening,

I am entirely new to asking questions here, so sorry if I did this wrong. I am trying to append one whole .txt file to end of another one, on a new line, without rewriting the contents.

For example, I have this in one.txt

TEST 1 00001 BCOM

and I have this in two.txt,

TEST 2 00001 BCOM

This is the only working code I found that would copy/overwrite to another file, All others I've copied, reworked with file paths and names and tried and it doesn't work for me. I am still a beginner in Java.

import java.io.*;
class CompileData {
    public static void main(String args[]) {
        FileReader fr = null;
        FileWriter fw = null;
        try {
            fr = new FileReader("one.txt");
            fw = new FileWriter("two.txt");
            int c = fr.read();
            while(c!=-1) {
                fw.write(c);
                c = fr.read();
            }
        } catch(IOException e) {
            e.printStackTrace();
        } finally {
            close(fr);
            close(fw);
        }
    }
    public static void close(Closeable stream) {
        try {
            if (stream != null) {
                stream.close();
            }
        } catch(IOException e) {
        }
    }
}

With this code, instead of getting this for two.txt

TEST 1 00001 BCOM
TEST 2 00002 BCOM

I only get for two.txt

TEST 1 00001 BCOM

Any help, tips, pointers and answers will be gladly appreciated!

Answer 1

For this, you can use append feature of FileWriter - by calling the parameterized constructor which accept the boolean whether to append or not.

Check here File Writer - append

import java.io.*;

class CompileData {
    public static void main(String args[]) {
        FileReader fr = null;
        FileWriter fw = null;
        try {
            fr = new FileReader("one.txt");

            fw = new FileWriter("two.txt",true);

            int c = fr.read();
            fw.write("\r\n");
            while(c!=-1) {
                fw.write(c);
                c = fr.read();
            }
        } catch(IOException e) {
            e.printStackTrace();
        } finally {
            close(fr);
            close(fw);
        }
    }
    public static void close(Closeable stream) {
        try {
            if (stream != null) {
                stream.close();
            }
        } catch(IOException e) {
        }
    }
}

Output

TEST 2 00002 BCOM
TEST 1 00001 BCOM

If you would like to append in start of file, you can use RandomAccessFile to append in desired location. More details here - RandomAccessFile API

RandomAccessFile f = new RandomAccessFile(new File("two.txt"), "rw");
f.seek(0); 
f.write("TEST 1 00001 BCOM".getBytes());
f.close();