DataTable不显示信息JSF

Question

我遇到了DataTable的问题。 我有一个 SelectOneMenu 组件，有3个选项。每个选项都应使用不同的信息呈现 DataTable 。

我的 xhtml 页面正在运行（我使用简单的代码对其进行了测试），但似乎我的支持bean 无法按照我的预期运行。当我运行页面时抛出一条错误消息。

我的xhtml看起来像

<h:form>
        <h:outputLabel for="reporte" value="Tipo de reporte: " />
        <h:selectOneMenu id="reporte"
                         value="#{reportController.type}">
            <f:selectItem itemLabel="Seleccione tipo de reporte..." itemValue="null" />
            <f:selectItems value="#{reportController.reportType}" />
            <f:ajax execute="@form" render="@form" />
        </h:selectOneMenu>




        <h:panelGrid id="porSistema"
                     rendered="#{reportController.type == 'Por sistema'}">
            <h:dataTable value="#{reportController.list}" var="item"
                         border="1">
                <h:column>
                    <f:facet name="header">
                        <h:outputText value="Nombre del archivo"/>
                    </f:facet>
                    <h:outputText value="#{item.fileName}"/>
                </h:column>
                <h:column>
                    <f:facet name="header">
                        <h:outputText value="Registros correctos"/>
                    </f:facet>
                    <h:outputText value="#{item.registersOk}"/>
                </h:column>
                <h:column>
                    <f:facet name="header">
                        <h:outputText value="Registros incorrectos"/>
                    </f:facet>
                    <h:outputText value="#{item.registersNok}"/>
                </h:column>
                <h:column>
                    <f:facet name="header">
                        <h:outputText value="Registros procesados"/>
                    </f:facet>
                    <h:outputText value="#{item.registers}"/>
                </h:column>
            </h:dataTable>
        </h:panelGrid>
    </h:form>

豆是

@ManagedBean
@ViewScoped
public class ReportController {

    List<Object> list = new ArrayList<Object>();
    String type;
    String[] reportType = new String[]{"Por sistema",
        "Por programa y componente",
        "Por estatus de pago"};

    @PostConstruct
    public void init() {
        if (type.equals("Por sistema")) {
            list.add(new ReporteSistema("A", "B", "C", "D"));
        } else if (type.equals("Por programa y componente")) {
            list.add(new ReporteProgramaComponenteA("E", "F", "G", "H", "I", "J"));
        } else if (type.equals("Por estatus de pago")) {
            list.add(new ReporteProgramaComponenteB("K", "L", "M", "N"));
        }
    }

    public String[] getReportType() {
        return reportType;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public List<Object> getList() {
        return list;
    }

    public void setList(List<Object> list) {
        this.list = list;
    }
}

并且堆栈跟踪是

com.sun.faces.mgbean.ManagedBeanCreationException: Se ha producido un error al realizar la inyección de recurso en el bean administrado reportController
    at com.sun.faces.mgbean.BeanBuilder.invokePostConstruct(BeanBuilder.java:229)
    at com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:105)
    at com.sun.faces.mgbean.BeanManager.createAndPush(BeanManager.java:409)
    at com.sun.faces.mgbean.BeanManager.create(BeanManager.java:269)
    at com.sun.faces.el.ManagedBeanELResolver.resolveBean(ManagedBeanELResolver.java:244)
    at com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:116)
    at com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176)
    at com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203)
    at org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:71)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:147)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
    at javax.faces.component.UIOutput.getValue(UIOutput.java:169)
    at com.sun.faces.renderkit.html_basic.MenuRenderer.getCurrentSelectedValues(MenuRenderer.java:648)
    at com.sun.faces.renderkit.html_basic.MenuRenderer.renderOptions(MenuRenderer.java:749)
    at com.sun.faces.renderkit.html_basic.MenuRenderer.renderSelect(MenuRenderer.java:844)
    at com.sun.faces.renderkit.html_basic.MenuRenderer.encodeEnd(MenuRenderer.java:298)
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1764)
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:168)
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1757)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1760)
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1760)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:401)
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:594)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at mx.gob.sagarpa.NoCacheFilter.doFilter(NoCacheFilter.java:29)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.myfaces.webapp.filter.ExtensionsFilter.doFilter(ExtensionsFilter.java:349)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:563)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:399)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:317)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:204)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:311)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)
Caused by: com.sun.faces.spi.InjectionProviderException
    at com.sun.faces.vendor.WebContainerInjectionProvider.invokeAnnotatedMethod(WebContainerInjectionProvider.java:119)
    at com.sun.faces.vendor.WebContainerInjectionProvider.invokePostConstruct(WebContainerInjectionProvider.java:99)
    at com.sun.faces.mgbean.BeanBuilder.invokePostConstruct(BeanBuilder.java:223)
    ... 56 more
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.GeneratedMethodAccessor85.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.sun.faces.vendor.WebContainerInjectionProvider.invokeAnnotatedMethod(WebContainerInjectionProvider.java:117)
    ... 58 more
Caused by: java.lang.NullPointerException
    at mx.gob.sagarpa.beans.ReportController.init(ReportController.java:32)
    ... 62 more

Answer 1

你的问题显然在stacktrace中说明了。您的init方法投放了NullPointerException。确切地说，您的type变量没有给出任何值。你无法用它来调用equals函数。

Answer 2

您似乎误解了@PostConstruct的目的。此注释用于指定在构造bean之后直接执行的方法。此注释允许您在注入@ManagedProperty指定的托管属性以及@Inject或@EJB等所有其他依赖项后执行代码。那些注入的属性和依赖项在bean的构造函数中是不可用的（当然，在完成所有注入之前，必须首先获得完全构造的bean实例）。当您在其上发送ajax请求时，不会调用视图范围bean的@PostConstruct。它只在您最初在浏览器中打开页面时调用。

实际上，您希望在触发ajax事件时调用该方法。您需要更改视图和bean，如下所示，以使其工作。

<h:selectOneMenu id="reporte" value="#{reportController.type}">
    <f:selectItem itemLabel="Seleccione tipo de reporte..." itemValue="null" />
    <f:selectItems value="#{reportController.reportType}" />
    <f:ajax execute="@form" listener="#{reportController.changeType}" render="@form" />
</h:selectOneMenu>

（请注意新的listener属性）

和

public void changeType() { // No, do not put @PostConstruct on it!
    if ("Por sistema".equals(type)) {
        list.add(new ReporteSistema("A", "B", "C", "D"));
    } else if ("Por programa y componente".equals(type)) {
        list.add(new ReporteProgramaComponenteA("E", "F", "G", "H", "I", "J"));
    } else if ("Por estatus de pago".equals(type)) {
        list.add(new ReporteProgramaComponenteB("K", "L", "M", "N"));
    }
}

另请注意，我交换了equals()的两面，以便您可以保证它永远不会抛出NPE。如果type恰好是null，那么它将被简单地比较为不相等。当您在equals()的某些内容上实际调用null时，您将确保获得一个NPE（这就是整个例外代表的内容！另请参阅its javadoc）。