modify file contents in place

First i list my question below:

1、i need to modify specific contents of a file in place

2、i do not want create a new file or rewrite the old file

And then i list the api i use below:

1、Scanner (to get the specitic contents we need to modify)

2、Random Access File(allows random access and writing to files on disk)

Note:replace specitic bytes with other bytes and cannot insert data into the middle of file.

to do that u need to rewrite evetything after the insertion point,just the same as the array process

All data after the insertion point of insertion would have to be moved to the right to accommodate the inserted data.

If you are replacing with a shorter string (i.e. removing bytes) then the data after the edit would have to be shifted left

// got the contents and reverse

Scanner scanner = new Scanner(new File("D:/test.txt")).useDelimiter("\\Z");
String contents = scanner.next();
System.out.println("Original String : " + contents);
contents = new StringBuffer(contents).reverse().toString();
System.out.println("Reversed String : " + contents);

// modify the contents of file
FileWriter fstream = new FileWriter("D:/test.txt");
BufferedWriter out = new BufferedWriter(fstream);
out.write(contents);
out.close();

// the below code show us how to use FileChannel

String s = "I was here!\n";
byte data[] = s.getBytes();
ByteBuffer out = ByteBuffer.wrap(data);

ByteBuffer copy = ByteBuffer.allocate(12);

try (FileChannel fc = (FileChannel.open(file, READ, WRITE))) {
    // Read the first 12
    // bytes of the file.
    int nread;
    do {
        nread = fc.read(copy);
    } while (nread != -1 && copy.hasRemaining());

    // Write "I was here!" at the beginning of the file.
    fc.position(0);
    while (out.hasRemaining())
        fc.write(out);
    out.rewind();

    // Move to the end of the file.  Copy the first 12 bytes to
    // the end of the file.  Then write "I was here!" again.
    long length = fc.size();
    fc.position(length-1);
    copy.flip();
    while (copy.hasRemaining())
        fc.write(copy);
    while (out.hasRemaining())
        fc.write(out);
} catch (IOException x) {
    System.out.println("I/O Exception: " + x);
}