code: private void restoreCommittedSize() throws IOException {
  
          check();
          long privCommittedSize=-1;
          this.getRandomAccessFile().seek(0);
          if (this.raf.length() < HEADER_LENGTH) {
              this.getRandomAccessFile().writeLong(0);
              privCommittedSize=0;
          } else {
              privCommittedSize = this.getRandomAccessFile().readLong();
          }
          this.position(privCommittedSize);
          this.committedSize=privCommittedSize;
      }
docs: restores the committed size  recored in the first 4 bytes of the file.     *
  the randomaccessFile is positioned to this position.
  
  The content beyond this new position is not destroyed but will be be overwritten,
  
  @throws java.io.IOException IO-Error
  @see