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jjnguy
jjnguy

Reputation: 138884

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

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

Upvotes: 18

Views: 16552

Answers (4)

Master
Master

Reputation: 683

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.

Upvotes: 0

jjnguy
jjnguy

Reputation: 138884

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();
}

Upvotes: 25

anjanb
anjanb

Reputation: 13867

Use RandomAccessFile

Upvotes: 6

Adam Rosenfield
Adam Rosenfield

Reputation: 400284

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.

Upvotes: 0

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