code: private static GroupTemplate createEngine(TemplateConfig config) {
  		if (null == config) {
  			config = new TemplateConfig();
  		}
  
  		switch (config.getResourceMode()) {
  		case CLASSPATH:
  			return createGroupTemplate(new ClasspathResourceLoader(config.getPath(), config.getCharsetStr()));
  		case FILE:
  			return createGroupTemplate(new FileResourceLoader(config.getPath(), config.getCharsetStr()));
  		case WEB_ROOT:
  			return createGroupTemplate(new WebAppResourceLoader(config.getPath(), config.getCharsetStr()));
  		case STRING:
  			return createGroupTemplate(new StringTemplateResourceLoader());
  		case COMPOSITE:
  			//TODO 需要定义复合资源加载器
  			return createGroupTemplate(new CompositeResourceLoader());
  		default:
  			return new GroupTemplate();
  		}
  	}
docs: 创建引擎
  
  @param config 模板配置
  @return {@link GroupTemplate}