code: public void prefetchStructure(String pdbId) throws IOException {
  		if ( pdbId.length() != 4)
  			throw new IOException("The provided ID does not look like a PDB ID : " + pdbId);
  
  		// Check existing
  		File file = downloadStructure(pdbId);
  
  		if(!file.exists()) {
  			throw new IOException("Structure "+pdbId+" not found and unable to download.");
  		}
  	}
docs: Download a structure, but don't parse it yet or store it in memory.
  
  Used to pre-fetch large numbers of structures.
  @param pdbId
  @throws IOException