@SessionScoped bean会丢失范围并一直重新创建，字段变为null

Question

我在JSF 2.0项目中使用SessionScoped bean时遇到了一个非常奇怪的问题。使用Netbeans 6.9.1，Glassfish 3服务器和PrimeFaces 3作为JSF组件库。

以下是一些代码：

package com.hia.jsf;

import com.hia.netlabel.jpa.Genre;
import com.hia.netlabel.jpa.Label;
import java.io.Serializable;
import java.util.List;
import javax.annotation.PostConstruct;
import javax.enterprise.context.SessionScoped;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ManagedProperty;

@ManagedBean
@SessionScoped
public class LabelDetailJSF implements Serializable{

@ManagedProperty("#{genreLabelListJSF}")
private GenreLabelListJSF genreLabelListJSF;
private List<Genre> DetailLabelGenreList;
private Label DetailLabel;
/** Creates a new instance of LabelDetailJSF */
public LabelDetailJSF() {
}
@PostConstruct
public void init(){
           System.out.print("Running init LabelDetailJSF");
           if(genreLabelListJSF.getSelectedLabel()!=null)
           {
                System.out.print("genreLabelListJSF was not null");
                this.DetailLabelGenreList=genreLabelListJSF.getSelectedLabel().getGenreList();
                this.DetailLabel= (genreLabelListJSF.getSelectedLabel());
           }
           if(this.DetailLabelGenreList==null){
               System.out.println("Bloody thing became null");

           }
}






/**
 * @return the DetailLabel
 */
public Label getDetailLabel() {
    return DetailLabel;
}

/**
 * @param DetailLabel the DetailLabel to set
 */
public void setDetailLabel(Label DetailLabel) {
    System.out.println("Setting Detail Label For LabelDetailJSF to:"+DetailLabel.getLabelName());
    this.DetailLabel = DetailLabel;

}

/**
 * @return the DetailLabelGenreList
 */
public List<Genre> getDetailLabelGenreList() {
    System.out.println("There is:"+this.DetailLabelGenreList.size()+ " Genres available");
    return DetailLabelGenreList;
}

/**
 * @param DetailLabelGenreList the DetailLabelGenreList to set
 */
public void setDetailLabelGenreList(List<Genre> DetailLabelGenreList) {
    System.out.println("Setting the DetailLabelGenre List to have "+DetailLabelGenreList.size());
    this.DetailLabelGenreList = DetailLabelGenreList;
}

/**
 * @return the genreLabelListJSF
 */
public GenreLabelListJSF getGenreLabelListJSF() {
    return genreLabelListJSF;
}

/**
 * @param genreLabelListJSF the genreLabelListJSF to set
 */
public void setGenreLabelListJSF(GenreLabelListJSF genreLabelListJSF) {
    this.genreLabelListJSF = genreLabelListJSF;
}

}

所以基本上我已经将另一个名为GenreLabelListJSF的sessioncoped bean注入LabelDetailJSF。我想在dataTable中显示DetailLabelGenreList。以下是用于显示数据表

的XHTML片段

<p:dataTable  id="detailLabelGenreGrid" value="#    {labelDetailJSF.detailLabelGenreList}" var="genre"  paginator="true"  styleClass="text70" rows="2" >
                            <p:column  style="min-width:196px;">
                                 #{genre.genreName}
                            </p:column> 
             </p:dataTable>

当页面加载时，我最初会获得包含一些行的表格。当我点击有趣的开始的分页按钮时。

我检查了所有System.out语句的输出，并在最初加载页面时发现以下内容。

INFO: Running init LabelDetailJSF
INFO: genreLabelListJSF was not null
INFO: There is:29 Genres available
INFO: There is:29 Genres available
INFO: There is:29 Genres available
INFO: There is:29 Genres available
INFO: There is:29 Genres available
INFO: There is:29 Genres available

当我点击数据表的页面按钮时，我得到以下内容：

INFO: Running init LabelDetailJSF
INFO: Bloody thing became null
SEVERE: javax.el.ELException: /LabelDetail.xhtml @62,165 value="#    {labelDetailJSF.detailLabelGenreList}": java.lang.NullPointerException
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:107)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:190)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:178)
    at javax.faces.component.UIData.getValue(UIData.java:554)
    at org.primefaces.component.datatable.DataTable.getValue(DataTable.java:731)
    at javax.faces.component.UIData.getDataModel(UIData.java:1248)
    at javax.faces.component.UIData.setRowIndex(UIData.java:447)
    at javax.faces.component.UIData.visitTree(UIData.java:1184)
    at javax.faces.component.UIComponent.visitTree(UIComponent.java:1457)
    at javax.faces.component.UIComponent.visitTree(UIComponent.java:1457)
    at javax.faces.component.UIForm.visitTree(UIForm.java:333)
    at javax.faces.component.UIComponent.visitTree(UIComponent.java:1457)
    at javax.faces.component.UIComponent.visitTree(UIComponent.java:1457)
    at com.sun.faces.application.view.StateManagementStrategyImpl.restoreView(StateManagementStrategyImpl.java:223)
    at com.sun.faces.application.StateManagerImpl.restoreView(StateManagerImpl.java:177)
    at com.sun.faces.application.view.ViewHandlingStrategy.restoreView(ViewHandlingStrategy.java:131)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.restoreView(FaceletViewHandlingStrategy.java:430)
    at com.sun.faces.application.view.MultiViewHandler.restoreView(MultiViewHandler.java:143)
    at com.sun.faces.lifecycle.RestoreViewPhase.execute(RestoreViewPhase.java:199)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.RestoreViewPhase.doPhase(RestoreViewPhase.java:110)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:312)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1523)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:215)
    at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:277)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:188)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:641)
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:97)
    at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:85)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:185)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:325)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:226)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:165)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:791)
    at com.sun.grizzly.comet.CometEngine.executeServlet(CometEngine.java:473)
    at com.sun.grizzly.comet.CometEngine.handle(CometEngine.java:341)
    at com.sun.grizzly.comet.CometAsyncFilter.doFilter(CometAsyncFilter.java:84)
    at com.sun.grizzly.arp.DefaultAsyncExecutor.invokeFilters(DefaultAsyncExecutor.java:161)
    at com.sun.grizzly.arp.DefaultAsyncExecutor.interrupt(DefaultAsyncExecutor.java:137)
    at com.sun.grizzly.arp.AsyncProcessorTask.doTask(AsyncProcessorTask.java:88)
    at com.sun.grizzly.http.TaskBase.run(TaskBase.java:189)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:330)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:309)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException
    at com.hia.jsf.LabelDetailJSF.getDetailLabelGenreList(LabelDetailJSF.java:72)
    at sun.reflect.GeneratedMethodAccessor951.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:302)
    at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:175)
    at com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:72)
    at com.sun.el.parser.AstValue.getValue(AstValue.java:116)
    at com.sun.el.parser.AstValue.getValue(AstValue.java:163)
    at com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:219)
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:102)
    ... 48 more

从我所看到的，它几乎就像bean失去了范围并且一直在重新创建。最初值是那里，当分页开始时bean失去了值。例如，我注意到@ManagedProperty bean在分页开始时也变为null。这有点疯狂，因为它也是一个会话范围的bean。

仍然是JSF的新手，所以我可能犯了一些noob错误。必须提一下，我最初是偶然地将它创建为ViewScoped bean，并且在将bean更改为SessionScoped之后，我取消部署了应用程序，重新启动了Glassfish并再次构建和部署它。

有什么想法吗？

Answer 1

您使用了错误的@SessionScoped注释。您正在使用CDI，而您使用JSF @ManagedBean注释而不是CDI @Named注释注册了bean。

替换CDI @SessionScoped导入

import javax.enterprise.context.SessionScoped;

由JSF @SessionScoped导入

import javax.faces.bean.SessionScoped;

另见：

• How to choose the right bean scope?
• Backing beans (@ManagedBean) or CDI Beans (@Named)?