code: static void initDrivers(final Config config) throws InitializationException {
        for(String driverName : uniquePrefixSet(config)) {
           Config driverConfig = config.getObject(driverName).toConfig();
           if(driverConfig.hasPath("class")) {
              String className = driverConfig.getString("class");
              try {
                 Class.forName(className);
              } catch(Throwable t) {
                 throw new InitializationException("Unable to load JDBC driver, '" + className + "'", t);
              }
           } else {
              throw new InitializationException("A 'class' must be specified for JDBC driver, '" + driverName + "'");
           }
        }
     }
docs: Initialize JDBC drivers from config.
  @throws InitializationException if driver could not be initialized