tdcommon/src/main/java/thredds/util/Constants.java
public static String setContentDispositionValue(String filename, String suffix) {
    int pos = filename.lastIndexOf('/');
    String outname = (pos > 0) ? filename.substring(pos+1) : filename;
    int pos2 = outname.lastIndexOf('.');
    outname = (pos > 0) ? outname.substring(0,pos2) : outname;
    outname = outname + suffix;
    return setContentDispositionValue(outname);
  }
public static String setContentDispositionValue(String filename, String suffix) {
    int pos = filename.lastIndexOf('/');
    String outname = (pos > 0) ? filename.substring(pos+1) : filename;
    int pos2 = outname.lastIndexOf('.');
    outname = (pos > 0) ? outname.substring(0,pos2) : outname;
    outname = outname + suffix;
    return setContentDispositionValue(outname);
  }
res.setHeader("Content-Disposition", "attachment; filename=" + path + ".nc");