cdm/src/main/java/ucar/nc2/NetcdfFile.java
@Override
  public long getLastModified() {
    if (spi != null && spi instanceof AbstractIOServiceProvider) {
      AbstractIOServiceProvider aspi = (AbstractIOServiceProvider) spi;
      return aspi.getLastModified();
    }
    return 0;
  }
@Override
  public long getLastModified() {
    if (spi != null && spi instanceof AbstractIOServiceProvider) {
      AbstractIOServiceProvider aspi = (AbstractIOServiceProvider) spi;
      return aspi.getLastModified();
    }
    return 0;
  }
/*
Check if file has changed, and reread metadata if needed.
All previous object references (variables, dimensions, etc) may become invalid - you must re-obtain.
DO NOT USE THIS ROUTINE YET - NOT FULLY TESTED

@return true if file was changed.
@throws IOException if error

public boolean sync() throws IOException {
unlocked = false;
return (spi != null) && spi.sync();
}