jsf - @SessionScoped bean 失去作用域并一直被重新创建，字段变为空

Question

JSF 2.0 项目中的 SessionScoped bean 有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。

这是一些代码:

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 sessionscoped bean 注入(inject)到 LabelDetailJSF 中。我想在数据表中显示 DetailLabelGenreList。这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，我最初得到包含一些行的表格。当我单击分页按钮时，这就是乐趣开始的地方。

我检查了所有 System.out 语句的输出，并在页面最初加载时发现了以下内容。

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

当我单击数据表的页面按钮时，我得到以下信息:

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

从我所见，这几乎就像 bean 失去了范围并一直在重新创建。最初这些值在那里，然后当分页开始时 bean 失去值。例如，我注意到@ManagedProperty bean 在分页开始时也变为空。这有点疯狂，因为它也是一个 session 范围的 bean。

仍然是 JSF 的新手，所以我可能犯了一些菜鸟错误。必须提到，我最初确实将其创建为 ViewScoped bean，但在将 bean 更改为 SessionScoped 后，我取消部署应用程序，重新启动 Glassfish 并再次构建和部署它。

有任何想法吗？

Answer 1

你用错了@SessionScoped注解。
如果您使用 JSF @ManagedBean 注册了 bean注解，则需要导入 @SessionScoped来自 JSF ( javax.faces ) 包，如下所示:

import javax.faces.bean.SessionScoped;

当您在 JSF 托管 bean 上错误地使用 CDI 范围时，JSF 托管 bean 实际上没有 JSF 范围，它会回退到其默认值 @RequestScoped ，它在每个 HTTP 请求中创建一个新实例。
如果您已使用 CDI @Named 注册了 bean注解，则需要导入 @SessionScoped来自 CDI ( javax.enterprise.context ) 包，如下所示:

import javax.enterprise.context.SessionScoped;

当您在 CDI 托管 bean 上错误地使用 JSF 范围时，CDI 托管 bean 实际上没有 CDI 范围，它会回退到其默认值 @Dependent作用域，它在每个 EL 表达式中创建一个新实例。
也可以看看:

How to choose the right bean scope?

Backing beans (@ManagedBean) or CDI Beans (@Named)?

What is the default Managed Bean Scope in a JSF 2 application?