Java. How to append text to top of file.txt [duplicate]

Question

This question already has an answer here:

• Writing in the beginning of a text file Java 5 answers

I need to add text to beggining of text file via Java.

For example I have test.txt file with data:

Peter
John
Alice

I need to add(to top of file):

Jennifer 

It should be:

Jennifer
Peter
John
Alice

I have part of code, but It append data to end of file, I need to make It that added text to top of file:

    public static void irasymas(String irasymai){
        try {
         File file = new File("src/lt/test.txt");

                if (!file.exists()) {
                file.createNewFile();
            }

            FileWriter fw = new FileWriter(file.getAbsoluteFile(), true);
            BufferedWriter bw = new BufferedWriter(fw);
            bw.write(irasymai+ "\r\n");
            bw.close();
} 
       catch (IOException e) {
        e.printStackTrace();                
        }
    }

I have tried this, but this only deletes all data from file and not insert any text:

public static void main(String[] args) throws IOException {
        BufferedReader reader = null;
        BufferedWriter writer = null;
        ArrayList list = new ArrayList();

        try {
            reader = new BufferedReader(new FileReader("src/lt/test.txt"));
            String tmp;
            while ((tmp = reader.readLine()) != null)
                list.add(tmp);
            OUtil.closeReader(reader);

            list.add(0, "Start Text");
            list.add("End Text");

            writer = new BufferedWriter(new FileWriter("src/lt/test.txt"));
            for (int i = 0; i < list.size(); i++)
                writer.write(list.get(i) + "\r\n");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            OUtil.closeReader(reader);
            OUtil.closeWriter(writer);
        }
    }

Thank you for help.

Answer 1

You can use RandomAccessFile to and seek the cursor to 0th position using seek(long position) method, before starting to write.

As explained in this thread

RandomAccessFile f = new RandomAccessFile(new File("yourFile.txt"), "rw");
f.seek(0); // to the beginning
f.write("Jennifer".getBytes());
f.close();

Edit: As pointed out below by many comments, this solution overwrites the file content from beginning. To completely replace the content, the File may have to be deleted and re-written.

Answer 2

File mFile = new File("src/lt/test.txt");
FileInputStream fis = new FileInputStream(mFile);
BufferedReader br = new BufferedReader(fis);
String result = "";
String line = "";
while( (line = br.readLine()) != null){
 result = result + line; 
}

result = "Jennifer" + result;

mFile.delete();
FileOutputStream fos = new FileOutputStream(mFile);
fos.write(result.getBytes());
fos.flush();

The idea is read it all, add the string in the front. Delete old file. Create the new file with eited String.

Answer 3

The below code worked for me. Again it will obviously replace the bytes at the beginning of the file. If you can certain how many bytes of replacement will be done in advance then you can use this. Otherwise, follow the earlier answers or take a look at here Writing in the beginning of a text file Java

    String str = "Jennifer";  
    byte data[] = str.getBytes();       

    try {                           
            RandomAccessFile f = new RandomAccessFile(new File("src/lt/test.txt"), "rw");
            f.getChannel().position(0);         
            f.write(data);
            f.close();
    } catch (IOException e) {       
            e.printStackTrace();
    }