Best Way to Write Bytes in the Middle of a File in Java

Question

What is the best way to write bytes in the middle of a file using Java?

Machellemachete

Answer 1

Reading and Writing in the middle of a file is as simple as using a RandomAccessFile in Java.

RandomAccessFile, despite its name, is more like an InputStream and OutputStream and less like a File. It allows you to read or seek through bytes in a file and then begin writing over whichever bytes you care to stop at.

Once you discover this class, it is very easy to use if you have a basic understanding of regular file i/o.

A small example:

public static void aMethod(){
    RandomAccessFile f = new RandomAccessFile(new File("whereDidIPutTHatFile"), "rw");
    long aPositionWhereIWantToGo = 99;
    f.seek(aPositionWhereIWantToGo); // this basically reads n bytes in the file
    f.write("Im in teh fil, writn bites".getBytes());
    f.close();
}

Machellemachete

what if i do not know the position or if i have hundreds of files where i have to insert data in the middle of them after some specified text? – Corned

If you do not know the position, then you need to open the file and read it to find where you need to write. – Machellemachete

my "file.txt" contains text like this "hi how you (newline) I am fine thanks" now i want to insert "are" in the middle of the text what i have to do? while doing this please mind that we are working with high amount of sized files – Corned

Note that the RandomAccessFile would overwrite the current content of the file from aPositionWhereIWantToGo – Brandes

Answer 2

Use RandomAccessFile

• Tutorial
• Javadocs

Impolitic

The tutorial linked to doesn't actually mention the RandomAccessFile class. Maybe this one instead: tutorials.jenkov.com/java-io/randomaccessfile.html – Pew

Answer 3

Open the file in write mode without truncating it, seek to the desired offset, and write the desired data. Just be careful about text/binary mode.

Fief

Answer 4

I think it’s best to create file chunks every time. And when the file is downloaded, connect them together. Now I'm working on it.

Lute