code: public void setGlobal(Object key, Object value) {
  		for (Scope cur=this; true; cur=cur.parent) {
  			if (cur.parent == null) {
  				cur.data.put(key, value);
  				return ;
  			}
  		}
  	}
docs: 设置全局变量
  全局作用域是指本次请求的整个 template