我正在使用 JSF 2.0 facelet，我正在努力从数据库中获取选定的项目值，我尝试了@PostConstruct方法，但它抛出了一个 excpetion，我会尽快写下所有内容，
我尝试了相同的数据库连接和实体，它运行良好。
我还应该提到，这里我使用字符串发送到 selectItems，在我使用 SelectItem List 之前，但它也不起作用，
有趣的是，当我错误地在 while 循环中插入一个 try and catch 块（你稍后会看到）时，它一遍又一遍地抛出异常，这意味着列表不是空的，但它只是没有到达页面。
造成这种情况的是什么云？
我的 jsf 代码
<h:selectOneMenu >
<f:selectItems value="#{settingsBean.countryItems}" />
</h:selectOneMenu>
我的管理豆
@Named(value = "settingsBean")
@RequestScoped公共类设置豆 {
/**
* Creates a new instance of SettingsBean
*/
private String favorits;
private String hobbies;
private String aboutme;
private String education;
private String country;
private String listCountry;
private List<String> countryItems;
private List<Countries> countries;
@EJB
CountriesFacadeLocal cin = new CountriesFacade();
public SettingsBean() {
}
@PostConstruct
public void init()
{
countries = cin.getAll();
if(!countries.isEmpty())
{
int i =0;
ListIterator iterator = countries.listIterator();
while(iterator.hasNext())
{
listCountry = countries.get(i).getCountry();
countryItems.add(i, listCountry);
}
}
}
我的国家外观代码
@Override
public List<Countries> getAll()
{
try{
em.flush();
Query query = em.createNamedQuery("Countries.findAll");
List<Countries> countryList = query.getResultList();
if(countryList!= null)
{
return countryList;
}
else
return null;
}
catch(Exception e)
{
return null;
}
}
我的堆栈跟踪
org.jboss.weld.exceptions.WeldException: WELD-000049 Unable to invoke [method] @PostConstruct public com.readme.user.signup.SettingsBean.init() on com.readme.user.signup.SettingsBean@606e86
at org.jboss.weld.bean.AbstractClassBean.defaultPostConstruct(AbstractClassBean.java:595)
at org.jboss.weld.bean.ManagedBean$ManagedBeanInjectionTarget.postConstruct(ManagedBean.java:200)
at org.jboss.weld.bean.ManagedBean.create(ManagedBean.java:340)
at org.jboss.weld.context.AbstractContext.get(AbstractContext.java:121)
at org.jboss.weld.bean.proxy.ContextBeanInstance.getInstance(ContextBeanInstance.java:99)
at org.jboss.weld.bean.proxy.ProxyMethodHandler.invoke(ProxyMethodHandler.java:87)
at com.readme.user.signup.org$jboss$weld$bean-web-ManagedBean-class_com$readme$user$signup$SettingsBean_$$_WeldClientProxy.getFavorits(org$jboss$weld$bean-web-ManagedBean-class_com$readme$user$signup$SettingsBean_$$_WeldClientProxy.java)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at javax.el.BeanELResolver.getValue(BeanELResolver.java:302)
at com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176)
at com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203)
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 org.jboss.weld.el.WeldValueExpression.getValue(WeldValueExpression.java:55)
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.HtmlBasicInputRenderer.getValue(HtmlBasicInputRenderer.java:205)
at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:355)
at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:164)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875)
at com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeRecursive(HtmlBasicRenderer.java:312)
at com.sun.faces.renderkit.html_basic.GridRenderer.renderRow(GridRenderer.java:185)
at com.sun.faces.renderkit.html_basic.GridRenderer.encodeChildren(GridRenderer.java:129)
at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1756)
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:1756)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1759)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:401)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:288)
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.StandardWrapper.service(StandardWrapper.java:1539)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:98)
at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:91)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:162)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:330)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:174)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:828)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:725)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1019)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:225)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
at java.lang.Thread.run(Thread.java:722)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.jboss.weld.util.reflection.SecureReflections$13.work(SecureReflections.java:305)
at org.jboss.weld.util.reflection.SecureReflectionAccess.run(SecureReflectionAccess.java:54)
at org.jboss.weld.util.reflection.SecureReflectionAccess.runAsInvocation(SecureReflectionAccess.java:163)
at org.jboss.weld.util.reflection.SecureReflections.invoke(SecureReflections.java:299)
at org.jboss.weld.introspector.jlr.WeldMethodImpl.invoke(WeldMethodImpl.java:193)
at org.jboss.weld.bean.AbstractClassBean.defaultPostConstruct(AbstractClassBean.java:591)
... 66 more
Caused by: java.lang.NullPointerException
at com.readme.user.signup.SettingsBean.init(SettingsBean.java:56)
... 76 more
原因是 SettingsBean 第 56 行中的 NullPointerException。我不知道这一行写了什么，但是检查您的代码，可能是类变量countryItems从未初始化过。
不要将 EJB 注解与新的如国家外观本地 cin = 新国家外观（）;如果您决定使用容器逻辑作为 EJB，您应该坚持这一点。否则，您的字段根本不会初始化（既不是 EJB 也不是 new），因此会变为空值。