Question

我在xhtml中使用“c：forEach”，方法如下：

<ui:composition xmlns="http://www.w3.org/1999/xhtml"
            xmlns:h="http://java.sun.com/jsf/html"
            xmlns:f="http://java.sun.com/jsf/core"
            xmlns:ui="http://java.sun.com/jsf/facelets"
            xmlns:fn="http://java.sun.com/jsp/jstl/functions"
            xmlns:c="http://xmlns.jcp.org/jsp/jstl/core"
            >

  <h:head>
    <!--I have tried to incorporate this set inside h:form as well. Still multiple calls-->
    <c:set var="currentHistory"  value="${itemBean.getParticipantItems(itemBean.history_id, 'borrow')}" />
<c:set value="${fn:length(currentHistory) - 1}" var="sizeOfCurrentHistory" />

  </h:head>

  <h:form enctype="multipart/form-data" >
     <body  >

     <!--I have tried with dataTable and ui:repeat.  Still multiple calls. And used step/begin in foreach-->
       <c:forEach  items="${currentHistory}" var="history" rendered="${fn:length(currentHistory) > 0}" >

         <div  >

           <h:outputLabel for="itemDescription" value="Item Description:" >
             <h:outputText  id="itemDescription" value="#   {history.itemDescription}" style="margin-left:10px;color:black;"/>
           </h:outputLabel>
           <br />
            <h:outputLabel for="itemModel" value="Item Model:" >
             <h:outputText  id="itemModel" value="#{history.itemModel}" style="margin-left:10px;color:black;"/>
        </h:outputLabel>
        <br />
        <h:outputLabel value="Item Approved:" >
          <h:outputText   value="Yes" style="margin-left:10px;color:black;"  rendered="${history.approved == 1}"/>
          <h:outputText  value="No" style="margin-left:10px;color:black;"  rendered="${history.approved == 0}"/>
        </h:outputLabel>
        <br />
        <h:outputLabel value="Date Created:" >
              <h:outputText  value="#{history.dateCreated}" style="margin-left:10px;color:black;"/>
      </div>
   </c:forEach>

</body>

bean调用代码如下： @Named @SessionScoped 公共类ItemBean扩展AbstractBean实现Serializable {

我介绍了一个测试结果的存在，但是没有用。

public List getParticipantItems(String pid, String which) {

System.out.println("called getParticipantItems");
List result = null;
Session session = null;
Transaction tx = null;
String query = null;
this.itemType = which;

if (this.itemFoundList == null) {
  // which_history: 0 = individual, 1 = community
  try {
    session = hib_session();
    tx = session.beginTransaction();
    if (this.history_which == 0) {
      query = " SELECT itm "
              + " FROM Items itm "
              + " WHERE itm.participant_id = :pid AND itm.itemType = :itype ORDER BY itm.dateCreated ";
    } else if (this.history_which == 1) {
      query = " SELECT itm "
              + " FROM Participant part, Items itm "
              + " INNER join part.item itm "
              + " WHERE part.communityId = :pid AND itm.itemType = :itype ORDER BY itm.dateCreated ";
    } else {
      //  Later query = "FROM Items WHERE participant_id = :pid and itemType = :it";
    }

    result = session.createQuery(query)
            .setParameter("pid", pid)
            .setParameter("itype", which)
            .list();
    tx.commit();
  } catch (Exception e) {
    tx.rollback();
    System.out.println("Error in getParticipantItems");
    Logger.getLogger(ItemBean.class.getName()).log(Level.SEVERE, null, e);

  } finally {
    tx = null;
    session = null;

  }
  this.itemFoundList = result;
}

if (this.itemFoundList != null) {
  return this.itemFoundList;
} else {
  return result;
}

}

有人可以帮助我理解为什么foreach中的这个支持bean被多次调用了吗？

感谢。

Answer 1

使用c：set设置的变量具有特定范围。默认范围是页面范围，这意味着每次访问变量时都会评估变量。这就是多次调用getParticipantItems方法的原因。其他范围是请求，会话和应用程序：

请求范围：为每个请求评估变量
会话范围：每个会话评估一次变量
应用程序范围：变量仅被评估一次，并且对于每个客户端都是相同的

尝试将c：的范围属性设置为请求：

    <c:set scope="request" ... />

JSF getter方法多次调用

1 个答案: