在ui:repeat中使用动态ui:include会导致NullPointerException [英] Using dynamic ui:include inside ui:repeat results in NullPointerException

问题描述

我想通过将<ui:repeat>和<p:dialog>与<ui:include>一起使用来创建动态对话框窗口.但是当我尝试如下所示时，会有一个例外.

I want to create dynamic dialog windows by using <ui:repeat> and <p:dialog> with <ui:include>. But there's an exception when I tried like below.

main.xhtml

<p:outputPanel id="windowsPanel" layout="block" style="width:100%;">
    <p:outputPanel rendered="#{mainView.dynamicWindows ne null}">
        <ui:repeat var="item"  value="#{mainView.dynamicWindows}">
            <p:dialog binding="#{item.dialog}">
                <ui:include src="#{item.includedWindowPath}" />
            </p:dialog>
        </ui:repeat>
    </p:outputPanel>
</p:outputPanel>

MainView.java

@ManagedBean(name = "mainView")
@SessionScoped
public class MainView extends BaseView {

private static final long serialVersionUID = -6291834350102049312L;

private List<Window> dynamicWindows;

@PostConstruct
public void init() {
    fillWindows();
}

private void fillWindows() {
    dynamicWindows = new ArrayList<Window>();

    for (int i = 0; i < 3; i++) {
        Window window = new Window("Header " + i);
        window.getDialog().setId("_dynamicWindow" + i);
        window.getDialog().setWidgetVar("_dynamicWindowWidget" + i);
        dynamicWindows.add(window);
    }
}

// getters & setters

例外:

javax.servlet.ServletException: /main.xhtml @33,42 binding="#{item.dialog}": Target Unreachable, identifier 'item' resolved to null
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:422)
    org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:79)
    org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:369)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:109)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:381)
    org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:97)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:381)
    org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:100)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:381)
    org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:78)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:381)
    org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:381)
    org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:35)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:381)
    org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:187)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:381)
    org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:381)
    org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:79)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:381)
    org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:168)
    org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237)
    org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167)
    org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)

推荐答案

<ui:include>是在视图构建时运行的标记处理程序，而<ui:repeat>是在视图渲染时运行的UI组件.标记处理程序产生JSF UI组件树. JSF UI组件生成HTML.它们不会同步运行.

The <ui:include> is a tag handler which runs during view build time, while the <ui:repeat> is an UI component which runs during view render time. Tag handlers produces the JSF UI component tree. JSF UI components produces HTML. They do not run in sync.

因此，当<ui:include>运行时，<ui:repeat var>指定的#{item}在范围内根本不可用，因为当时<ui:repeat>尚未运行.您需要一个迭代的标记处理程序，而不是一个迭代的JSF UI组件. JSTL <c:forEach>就是这样的.用<c:forEach>替换<ui:repeat>应该可以解决此问题.然而，它可能有不良的副作用.由于您的具体功能要求尚不完全清楚，因此很难事先告知.

So, when the <ui:include> runs, the #{item} which is specified by <ui:repeat var> is simply not available in the scope, because the <ui:repeat> hasn't run at that time. You need an iterating tag handler instead of an iterating JSF UI component. The JSTL <c:forEach> is such one. Replacing <ui:repeat> by <c:forEach> should fix this issue. It may however have undesireable side effects. It's hard to tell beforehand as your concrete functional requirements are not fully clear.

• JSF2 Facelets中的JSTL是有意义的吗?(讨论生命周期标签处理程序与UI组件的对比)

• JSTL in JSF2 Facelets... makes sense? (discusses lifecycle of tag handlers vs UI components)

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