code: @Override
    public void dropCollection(String collectionName) {
      CollectionMetaData cmd = cmdMap.get(collectionName);
      if((null == cmd) || (!collectionsRef.get().containsKey(collectionName))) {
        throw new InvalidJsonDbApiUsageException("Collection by name '" + collectionName + "' not found. Create collection first.");
      }
      cmd.getCollectionLock().writeLock().lock();
      try {
        File toDelete = fileObjectsRef.get().get(collectionName);
        try {
          Files.deleteIfExists(toDelete.toPath());
        } catch (IOException e) {
          logger.error("IO Exception deleting the collection file {}", toDelete.getName(), e);
          throw new InvalidJsonDbApiUsageException("Unable to create a collection file for collection: " + collectionName);
        }
        //cmdMap.remove(collectionName); //Do not remove it from the CollectionMetaData Map.
        //Someone might want to re insert a new collection of this type.
        fileObjectsRef.get().remove(collectionName);
        collectionsRef.get().remove(collectionName);
        contextsRef.get().remove(collectionName);
      } finally {
        cmd.getCollectionLock().writeLock().unlock();
      }
    }
docs: /* (non-Javadoc)
  @see io.jsondb.JsonDBOperations#dropCollection(java.lang.String)