cdm/src/main/java/ucar/nc2/util/DiskCache.java
static public void cleanCache(Date cutoff, StringBuilder sbuff) {
    if (sbuff != null) sbuff.append("CleanCache files before ").append(cutoff).append("\n");
    File dir = new File(root);
    File[] children = dir.listFiles();
    if (children == null) return;
    for (File file : children) {
      Date lastMod = new Date(file.lastModified());
      if (lastMod.before(cutoff)) {
        boolean ret = file.delete();
        if (sbuff != null) {
          sbuff.append(" delete ").append(file).append(" (").append(lastMod).append(")\n");
          if (!ret) sbuff.append("Error deleting ").append(file).append("\n");
        }
      }
    }
  }
static public void cleanCache(Date cutoff, StringBuilder sbuff) {
    if (sbuff != null) sbuff.append("CleanCache files before ").append(cutoff).append("\n");
    File dir = new File(root);
    File[] children = dir.listFiles();
    if (children == null) return;
    for (File file : children) {
      Date lastMod = new Date(file.lastModified());
      if (lastMod.before(cutoff)) {
        boolean ret = file.delete();
        if (sbuff != null) {
          sbuff.append(" delete ").append(file).append(" (").append(lastMod).append(")\n");
          if (!ret) sbuff.append("Error deleting ").append(file).append("\n");
        }
      }
    }
  }
Remove all files with date < cutoff.

@param cutoff earliest date to allow
@param sbuff  write results here, null is ok.