java - 运行它但在 s :iterator tag 中没有显示

Question

我用

<class name="Topic" table="topic">     
         .......
  <set name="replies" inverse="true" lazy="false"  cascade="save-update">
        <key column="TOPIC_ID"/>
        <one-to-many class="Reply"/>
  </set>
</class>

而且我看到 replies 不是 null 并且在 topic.replies 中有元素；

Topic topic = topicService.getTopicById(topicId);
ActionContext actionContext = getActionContext();
actionContext.put("topic", topic);

在 JSP 中:

<s:iterator value="#topic.replies">
  <s:property value="title"/>
</s:iterator>

无标题显示。 然后我更改我的代码

Topic topic = topicService.getTopicById(topicId);
ActionContext actionContext = getActionContext();
actionContext.put("replies", topic.getReplies);

在 JSP 中

<s:iterator value="#replies">
  <s:property value="title"/>
</s:iterator>

显示标题的值。

我不知道为什么标题不是第一种方式显示。

Answer 1

为什么要那样使用 ActionContext？

ActionContext 对于从其他地方(例如 Helper 类)访问数据(已对 Action 可用)很有用，无需传递任何参数。

来自文档:What is the ActionContext

To keep signatures brief, and methods useful, the framework uses two techniques: Dependency Injection and Thread Local, both of which, in turn, rely on the ActionContext.

From anywhere within an Struts 2 application, you can obtain a reference to the [ActionContext] by calling

  ActionContext context = ActionContext.getContext();

For example, if a helper class is called from an Action, and if it happens to need access to ServletContext (maybe it is writing a file and needs ServletContext to get a path to it), the helper can obtain the ActionContext directly. Nothing needs to be passed from the Action.

JSP 属性通常从 Action 中读取，并且 Action 必须通过访问器(或 getter )公开这些属性；只需将 Hibernate 结果映射到 Action 中的某个 DTO。