Java. How to append text to top of file.txt

Question

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.

I don't think so, I just posted 1 of many solutions what I have tried. — , May 21 '13 at 08:23

score 5 · Answer 1 · answered May 21 '13 at 08:34

5

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.

answered May 21 '13 at 08:34

Jeff Lee

783
9
17

Thank you for answer, but in this line `BufferedReader br = new BufferedReader(fis);` I got error: `The Constructor BufferedReader(FileInputStream) is undefined`. – May 21 '13 at 08:39
1

@Rimantė Baltiejūtė Sorry missing something BufferecReader(new InputStreamReader(new FileInputStream())) – Jeff Lee May 21 '13 at 08:45
Please use StingBuffer – user666 Dec 16 '16 at 11:44
You should fix example to `new BufferedReader(new InputStreamReader` – zygimantus Oct 22 '18 at 18:55

score -3 · Accepted Answer · edited May 23 '17 at 12:34

-3

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.

edited May 23 '17 at 12:34

Community

1
1

answered May 21 '13 at 08:16

sanbhat

17,522
6
48
64

Thank you for answer. I have been tried RandomAccessFile, but unsuccessfuly. Could you help me with It a little bit, please? – May 21 '13 at 08:17
And what is "rw" here? – May 21 '13 at 08:28
1

`rw` is a mode. That means you are opening the file to both `r` - read `w` - write. for your need `w` is enough, because you are only writing. – sanbhat May 21 '13 at 08:28
Thank you for code, but this working incorrect. It not appeding, but deleting first line. If my file looks like `111 222 333 444` after I use this code It adding "Jennifer" to top of file, but It looks like: `Jennifer22 333 444` First line deleted and 2nd line half deleted. – May 21 '13 at 08:34
See http://docs.oracle.com/javase/tutorial/essential/io/rafs.html – sanbhat May 21 '13 at 08:50
3

Is this code overwriting or inserting? – Alexandre Lavoie May 21 '13 at 09:22
11

Overwriting first Line. – May 21 '13 at 09:29
3

This code doesn't work. It actually replaces existing bytes in the file, not inserts. – dessalines Jan 24 '15 at 16:44
9

THE ANSWER IS WRONG!!! – serg.nechaev Apr 20 '15 at 02:54
5

The answer is not correct because the RandomAccessFile would overwrite the current content of the file from position where f.seek(position); Better to convert the file into String and do String manipulation – super1ha1 Mar 29 '16 at 15:48

score -3 · Answer 3 · edited May 23 '17 at 12:34

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();
    }

Java. How to append text to top of file.txt

3 Answers3

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