Not able to read file using java.nio.channels.FileChannel

Question

I am doing following: - creating an empty file - locking file - write to file - reading back the content

public class TempClass {
public static void main(String[] args) throws Exception{
    File file = new File("c:/newfile.txt");
    String content = "This is the text content123";

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

        // get the content in bytes
        byte[] contentInBytes = content.getBytes();

        FileChannel fileChannel = new RandomAccessFile(file, "rw").getChannel();

        FileLock lock = fileChannel.lock();

        //write to file 
        fileChannel.write(ByteBuffer.wrap (contentInBytes));

        //force any updates to this channel's file                  
        fileChannel.force(false);

        //reading back file contents
        Double dFileSize = Math.floor(fileChannel.size());
        int fileSize = dFileSize.intValue();
        ByteBuffer readBuff = ByteBuffer.allocate(fileSize);
        fileChannel.read(readBuff);

        for (byte b : readBuff.array()) {
            System.out.print((char)b);
        } 
        lock.release();
       }    

}

However I can see the file is correctly written with the content I specified, but when I read it back, it prints square characters for all the actual characters in the file. That square character is char equivalent of the byte 0:

System.out.print((char)((byte)0));

Whats wrong here?

Answer 1

When reading back the file, you did not reset the position in which the FileChannel is currently at, thus when performing

fileChannel.read(readBuff);

Nothing is being allocated to the buffer as the FileChannel is positioned at the end of the file (causing your print code to show the 0-initialized values).

Perform:

fileChannel.position(0);

to reset the FileChannel to the start of the file.