code: public ArrayList<JTSFeature> getFeaturesByCategory(String category, int z, int x, int y, List<Param> optionalParams)
  			throws Exception {
  		List<String> ids = serviceManager.getAvailableServices().getServicesIDByCategory(category);
  		ArrayList<JTSFeature> features = new ArrayList<JTSFeature>();
  		for (String id : ids) {
  			try {
  				features.addAll(this.getFeatures(id, z, x, y, optionalParams));
  			} catch (Exception e) {
  				logger.error("POIProxy", e);
  			}
  		}
  
  		return features;
  	}
docs: This method is used to get the pois from a category and return a list of
  {@link JTSFeature} document with the data retrieved given a Z/X/Y tile.
  
  @param id
  The category to request
  @see #getAvailableCategories()
  @param z
  The zoom level
  @param x
  The x tile
  @param y
  The y tile
  @return a list of {@link JTSFeature}