数据库中的JSF2 Bean的一些数据在渲染时不可用(Some data of JSF2 Bean from database not available at render time)

 渲染JSF2（Facelet）页面时，我遇到了一个奇怪的问题。 通常是通过GET接收id并显示对象的页面。 该对象内部有一个List <>，问题是有时该列表不打印任何内容，有时我刷新并部分打印列表（所有元素但不是所有关于它们的信息）。 它也与其他对象的属性（某些日期）一起发生。 我已经检查了一些日志记录，并且从数据库和对象set正确获取了信息。 
 
 我很确定这是因为preRenderView是在渲染之前完成的，所以当我使用c:if或c:each时，bean很可能无法使用。 对于第二种情况，也许ui:repeat 会解决我的问题 ？ 
 
 我的问题是： 
 
 
 
 我怎样才能解决这个问题？ 
 
 
 在Facelets中有没有办法渲染f.ex. <section>或<time> （如下面的document.xhtml所示）如果渲染计算为false，则不打印空标记？ 我知道我可以使用c:if ，但在Facelets中推荐使用。 
 
 
 DB Javabean Document是否也被Named （除了DocumentController）？ 
 
 
 另外，如果有更好的方法来做我正在做的事情（通过GET接收id并显示对象的页面），请告知。 我是JSF的新手。 
 
 顺便说一句，我已经丢弃它是由于这个问题 。 
 
 DocumentController.java 
 
@Named(value = "DocumentController")
@SessionScoped
public class DocumentController implements Serializable {
    private String id;
    private Document document;

    /**
     * @return the id
     */
    public String getId() {
        return id;
    }

    /**
     * @param id the id to set
     */
    public void setId(String id) {
        this.id = id;
    }

    /**
     * @return the Document
     */
    public Document getDocument() {
        return document;
    }

    /**
     * @param Document the Document to set
     */
    public void setDocument(Document document) {
        this.document = document;
    }


    public void load() {
        FacesContext ctx = FacesContext.getCurrentInstance();
        if (ctx.isValidationFailed()) {
            ctx.getApplication().getNavigationHandler()
                    .handleNavigation(ctx, "#{DocumentController.load}", "invalid");
            return;
        }

        try (DataStore dst = new DataStore()) {
            dst.connect();
            document = dst.getDocument(id);

        } catch (NoData | ConnectionError | IllegalArgumentException ex) {
            ctx.getApplication().getNavigationHandler()
                    .handleNavigation(ctx, "#{DocumentController.load}", "invalid");
        }
    }

}
 
 document.xhtml 
 
<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://xmlns.jcp.org/jsf/facelets"
                xmlns:utils="http://java.sun.com/jsf/composite/utils"
                template="template.xhtml">
    <ui:define name="content">
        <f:metadata>
            <f:viewParam name="id" value="#{documentController.id}" required="true"/>
            <f:event type="preRenderView" listener="#{documentController.load}"/>
        </f:metadata>
...
        <section rendered="#{not empty documentController.document.participants}">
            <utils:participants
                participants="#{documentController.document.participants}
                cid="example"/>
....
    </ui:define>
</ui:composition>
 
 participants.xhtml 
 
<ui:component xmlns="http://www.w3.org/1999/xhtml"
              xmlns:h="http://java.sun.com/jsf/html"
              xmlns:f="http://java.sun.com/jsf/core"
              xmlns:cc="http://xmlns.jcp.org/jsf/composite"
              xmlns:c="http://java.sun.com/jsp/jstl/core"
              xmlns:ui="http://java.sun.com/jsf/facelets">
    <cc:interface>
        <cc:attribute name="participants" type="java.util.List" required="true"/>
        <cc:attribute name="cid" type="String" required="true"/>
    </cc:interface>

    <cc:implementation>
        <table>
...
            <tbody>
                <c:forEach items="#{cc.attrs.participants}" var="participant">
                    <tr>
                        <td><a href="#">#{participant.name}</a></td>
                        <td>#{participant.lastName}</td>
                        <td>#{participant.role(cc.attrs.cid)}</td>
                    </tr>
                </c:forEach>
            </tbody>
        </table>
    </cc:implementation>
</ui:component>

I am running into a weird problem when rendering JSF2 (Facelet) pages. It is the usual page that receives an id via GET and displays the object. The object has a List<> inside, and the problem is that sometimes that list prints nothing and sometimes I refresh and prints the list partially (all the elements but not all the information about them). It also happens with other object's attributes (some dates). I have checked with some logging and the information is obtained correctly from the DB and the object sets the information.
 
I am quite sure that this is because preRenderView is done just before the render, so the bean is by chance not available when I use c:if or c:each. For the second case, perhaps ui:repeat would solve my problem?.
 
My questions are:
 
 
 
How can I fix this?
 
 
Is there a way in Facelets, to render f.ex. a <section> or <time> (as in my document.xhtml below) and don't print the empty tag if rendered computes to false? I know I can use c:if, but rendered is recommended in Facelets.
 
 
Has the DB Javabean Document to be Named as well (besides DocumentController)?
 
 
Also, please, if there is a better way to do what I am doing (a page that receives an id via GET and displays the object), please advise. I am totally new to JSF.
 
Btw, I have discarded it is due to this problem.
 
DocumentController.java
 
@Named(value = "DocumentController")
@SessionScoped
public class DocumentController implements Serializable {
    private String id;
    private Document document;

    /**
     * @return the id
     */
    public String getId() {
        return id;
    }

    /**
     * @param id the id to set
     */
    public void setId(String id) {
        this.id = id;
    }

    /**
     * @return the Document
     */
    public Document getDocument() {
        return document;
    }

    /**
     * @param Document the Document to set
     */
    public void setDocument(Document document) {
        this.document = document;
    }


    public void load() {
        FacesContext ctx = FacesContext.getCurrentInstance();
        if (ctx.isValidationFailed()) {
            ctx.getApplication().getNavigationHandler()
                    .handleNavigation(ctx, "#{DocumentController.load}", "invalid");
            return;
        }

        try (DataStore dst = new DataStore()) {
            dst.connect();
            document = dst.getDocument(id);

        } catch (NoData | ConnectionError | IllegalArgumentException ex) {
            ctx.getApplication().getNavigationHandler()
                    .handleNavigation(ctx, "#{DocumentController.load}", "invalid");
        }
    }

}
 
document.xhtml
 
<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://xmlns.jcp.org/jsf/facelets"
                xmlns:utils="http://java.sun.com/jsf/composite/utils"
                template="template.xhtml">
    <ui:define name="content">
        <f:metadata>
            <f:viewParam name="id" value="#{documentController.id}" required="true"/>
            <f:event type="preRenderView" listener="#{documentController.load}"/>
        </f:metadata>
...
        <section rendered="#{not empty documentController.document.participants}">
            <utils:participants
                participants="#{documentController.document.participants}
                cid="example"/>
....
    </ui:define>
</ui:composition>
 
participants.xhtml
 
<ui:component xmlns="http://www.w3.org/1999/xhtml"
              xmlns:h="http://java.sun.com/jsf/html"
              xmlns:f="http://java.sun.com/jsf/core"
              xmlns:cc="http://xmlns.jcp.org/jsf/composite"
              xmlns:c="http://java.sun.com/jsp/jstl/core"
              xmlns:ui="http://java.sun.com/jsf/facelets">
    <cc:interface>
        <cc:attribute name="participants" type="java.util.List" required="true"/>
        <cc:attribute name="cid" type="String" required="true"/>
    </cc:interface>

    <cc:implementation>
        <table>
...
            <tbody>
                <c:forEach items="#{cc.attrs.participants}" var="participant">
                    <tr>
                        <td><a href="#">#{participant.name}</a></td>
                        <td>#{participant.lastName}</td>
                        <td>#{participant.role(cc.attrs.cid)}</td>
                    </tr>
                </c:forEach>
            </tbody>
        </table>
    </cc:implementation>
</ui:component>

原文：https://stackoverflow.com/questions/36457213