如何防止MappedByteBuffer put在文件末尾写入空字符？

import java.io.File;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class MappedByteBufferExample {
    public static void main(String[] args) throws Exception {
        File file = new File("example.txt");
        RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");
        FileChannel fileChannel = randomAccessFile.getChannel();

        // 将文件的一部分映射到内存中
        MappedByteBuffer mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, file.length());

        // 获取当前位置
        int currentPosition = mappedByteBuffer.position();

        // 获取文件的大小
        long fileSize = file.length();

        // 判断当前位置是否在文件末尾
        if (currentPosition != fileSize) {
            // 进行写入操作
            mappedByteBuffer.put((byte) 'A');
        }

        // 关闭资源
        fileChannel.close();
        randomAccessFile.close();
    }
}