具有字符串列表值的多个自动完成无法生成 Converter JSF？
Multiple Autocomplete with a value of a list of strings can't generate Converter JSF?
我目前正在做一个项目，我需要问题的标签（比如 Whosebug 标签）所以我使用了多重自动完成（它是一个 h:form）：
<p:autoComplete id="autoComplete" value="#{questionMB.tags}" completeMethod="#{questionMB.complete}" multiple="true" forceSelection="true" unique="true" />
这是questionMB
@Named
@ViewScoped
@RolesAllowed(value = { "ADMIN", "SUPERUSER", "USER" })
public class questionMB implements Serializable {
private static final long serialVersionUID = -4130025302903207410L;
private List<String> tags = new ArrayList<>();
//other vars...
public List<String> complete(String query) {
//retrieves data from database
return DBHelper.completeTag(query);
}
//other functions, getters and setter...
}
当我使用它时它抛出这个异常：
20:47:21,418 SEVERE [javax.enterprise.resource.webcontainer.jsf.application] (default task-8) Error Rendering View[/user/postRepair.xhtml]: java.lang.NullPointerException
at com.sun.faces.cdi.CdiUtils.createConverter(CdiUtils.java:102)
at com.sun.faces.application.applicationimpl.InstanceFactory.createConverter(InstanceFactory.java:481)
at com.sun.faces.application.ApplicationImpl.createConverter(ApplicationImpl.java:510)
at javax.faces.application.ApplicationWrapper.createConverter(ApplicationWrapper.java:431)
at org.omnifaces.cdi.converter.ConverterManager.createConverter(ConverterManager.java:155)
at org.omnifaces.cdi.converter.ConverterManager$Proxy$_$$_WeldClientProxy.createConverter(Unknown Source)
at org.omnifaces.application.OmniApplication.createConverter(OmniApplication.java:98)
at org.primefaces.util.ComponentUtils.getConverter(ComponentUtils.java:175)
at org.primefaces.component.autocomplete.AutoCompleteRenderer.encodeSuggestions(AutoCompleteRenderer.java:481)
at org.primefaces.component.autocomplete.AutoCompleteRenderer.encodeResults(AutoCompleteRenderer.java:136)
at org.primefaces.component.autocomplete.AutoCompleteRenderer.encodeEnd(AutoCompleteRenderer.java:117)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:595)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1654)
at com.sun.faces.context.PartialViewContextImpl$PhaseAwareVisitCallback.visit(PartialViewContextImpl.java:615)
at com.sun.faces.component.visit.PartialVisitContext.invokeVisitCallback(PartialVisitContext.java:159)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1456)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIForm.visitTree(UIForm.java:355)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at com.sun.faces.context.PartialViewContextImpl.processComponents(PartialViewContextImpl.java:400)
at com.sun.faces.context.PartialViewContextImpl.processPartial(PartialViewContextImpl.java:319)
at org.primefaces.context.PrimePartialViewContext.processPartial(PrimePartialViewContext.java:63)
at javax.faces.context.PartialViewContextWrapper.processPartial(PartialViewContextWrapper.java:228)
at org.omnifaces.context.OmniPartialViewContext.processPartial(OmniPartialViewContext.java:122)
at javax.faces.component.UIViewRoot.encodeChildren(UIViewRoot.java:1101)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1647)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:442)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:170)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at org.omnifaces.viewhandler.OmniViewHandler.renderView(OmniViewHandler.java:115)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:102)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:76)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:199)
at javax.faces.webapp.FacesServlet.executeLifecyle(FacesServlet.java:708)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:451)
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:74)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129)
at org.omnifaces.filter.GzipResponseFilter.doFilter(GzipResponseFilter.java:181)
at org.omnifaces.filter.HttpFilter.doFilter(HttpFilter.java:108)
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at com.github.adminfaces.template.session.AdminFilter.doFilter(AdminFilter.java:128)
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at io.opentracing.contrib.jaxrs2.server.SpanFinishingFilter.doFilter(SpanFinishingFilter.java:55)
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84)
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
at io.undertow.servlet.handlers.ServletChain.handleRequest(ServletChain.java:68)
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:132)
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
at io.undertow.server.handlers.DisableCacheHandler.handleRequest(DisableCacheHandler.java:33)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.security.handlers.AuthenticationConstraintHandler.handleRequest(AuthenticationConstraintHandler.java:53)
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
at io.undertow.servlet.handlers.security.ServletSecurityConstraintHandler.handleRequest(ServletSecurityConstraintHandler.java:59)
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jaspi.JASPICSecureResponseHandler.handleRequest(JASPICSecureResponseHandler.java:48)
at org.wildfly.extension.undertow.deployment.GlobalRequestControllerHandler.handleRequest(GlobalRequestControllerHandler.java:68)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292)
at io.undertow.servlet.handlers.ServletInitialHandler.access0(ServletInitialHandler.java:81)
at io.undertow.servlet.handlers.ServletInitialHandler.call(ServletInitialHandler.java:138)
at io.undertow.servlet.handlers.ServletInitialHandler.call(ServletInitialHandler.java:135)
at io.undertow.servlet.core.ServletRequestContextThreadSetupAction.call(ServletRequestContextThreadSetupAction.java:48)
at io.undertow.servlet.core.ContextClassLoaderSetupAction.call(ContextClassLoaderSetupAction.java:43)
at org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction.lambda$create[=12=](SecurityContextThreadSetupAction.java:105)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create[=12=](UndertowDeploymentInfoService.java:1502)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create[=12=](UndertowDeploymentInfoService.java:1502)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create[=12=](UndertowDeploymentInfoService.java:1502)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create[=12=](UndertowDeploymentInfoService.java:1502)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272)
at io.undertow.servlet.handlers.ServletInitialHandler.access[=12=]0(ServletInitialHandler.java:81)
at io.undertow.servlet.handlers.ServletInitialHandler.handleRequest(ServletInitialHandler.java:104)
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:364)
at io.undertow.server.HttpServerExchange.run(HttpServerExchange.java:830)
at org.jboss.threads.ContextClassLoaderSavingRunnable.run(ContextClassLoaderSavingRunnable.java:35)
at org.jboss.threads.EnhancedQueueExecutor.safeRun(EnhancedQueueExecutor.java:1982)
at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.doRunTask(EnhancedQueueExecutor.java:1486)
at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1377)
at java.lang.Thread.run(Unknown Source)
其他任何东西都没有问题，因为当我删除 value="#{questionMB.tags}" 时它完全可以正常工作，所以我可以删除、添加和搜索标签。但是当我添加值时：我输入一个字符（DBHelper.completeTag() 仍然可以正常工作，而 returns 值只是没有显示在 UI 中）并且抛出异常。
所以问题似乎是无法生成转换器（请参阅堆栈跟踪中的第 2 行）。所以我认为转换它应该没问题，因为我只使用字符串。可能列表有问题，无法转换。所以我找了两天也没找到一个可以回答我的问题。
编辑
我已经测试了哪些组件为空：DBHelper.completeTag() returns 一个很好的字符串列表，其中包含来自数据库的正确值。 List<String> tags = new ArrayList<>(); 初始化标签列表但没有字符串值（非空）。
我正在使用 Primefaces 7.0、OmniFaces 3.2、Mojarra 和 Primefaces-Extensions 6.1.1。
@Kukeltje 发现，这是一个已知问题：NPE when determining converter for primitive values。
据说解决方法是installing omnifaces 3.3。
实际修复计划在 Mojarra 2.3.10 版本 - Jakarta Faces 的参考实现中进行。
昨天我在评论中建议有人应该写 this 答案但是评论被删除了，所以我在这里尽管这不是我的发现。随意写另一个答案，这不是为了获得声誉，而是为其他遇到此问题的人提供路标。虽然疯狂地没有人对删除的评论有任何反馈，但我猜它被删除是因为我暗示 OP 肯定没有以讽刺的方式使用 Mojarra 的第 8 版。如果有人觉得被冒犯了，抱歉。
我目前正在做一个项目，我需要问题的标签（比如 Whosebug 标签）所以我使用了多重自动完成（它是一个 h:form）：
<p:autoComplete id="autoComplete" value="#{questionMB.tags}" completeMethod="#{questionMB.complete}" multiple="true" forceSelection="true" unique="true" />
这是questionMB
@Named
@ViewScoped
@RolesAllowed(value = { "ADMIN", "SUPERUSER", "USER" })
public class questionMB implements Serializable {
private static final long serialVersionUID = -4130025302903207410L;
private List<String> tags = new ArrayList<>();
//other vars...
public List<String> complete(String query) {
//retrieves data from database
return DBHelper.completeTag(query);
}
//other functions, getters and setter...
}
当我使用它时它抛出这个异常：
20:47:21,418 SEVERE [javax.enterprise.resource.webcontainer.jsf.application] (default task-8) Error Rendering View[/user/postRepair.xhtml]: java.lang.NullPointerException
at com.sun.faces.cdi.CdiUtils.createConverter(CdiUtils.java:102)
at com.sun.faces.application.applicationimpl.InstanceFactory.createConverter(InstanceFactory.java:481)
at com.sun.faces.application.ApplicationImpl.createConverter(ApplicationImpl.java:510)
at javax.faces.application.ApplicationWrapper.createConverter(ApplicationWrapper.java:431)
at org.omnifaces.cdi.converter.ConverterManager.createConverter(ConverterManager.java:155)
at org.omnifaces.cdi.converter.ConverterManager$Proxy$_$$_WeldClientProxy.createConverter(Unknown Source)
at org.omnifaces.application.OmniApplication.createConverter(OmniApplication.java:98)
at org.primefaces.util.ComponentUtils.getConverter(ComponentUtils.java:175)
at org.primefaces.component.autocomplete.AutoCompleteRenderer.encodeSuggestions(AutoCompleteRenderer.java:481)
at org.primefaces.component.autocomplete.AutoCompleteRenderer.encodeResults(AutoCompleteRenderer.java:136)
at org.primefaces.component.autocomplete.AutoCompleteRenderer.encodeEnd(AutoCompleteRenderer.java:117)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:595)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1654)
at com.sun.faces.context.PartialViewContextImpl$PhaseAwareVisitCallback.visit(PartialViewContextImpl.java:615)
at com.sun.faces.component.visit.PartialVisitContext.invokeVisitCallback(PartialVisitContext.java:159)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1456)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIForm.visitTree(UIForm.java:355)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at javax.faces.component.UIComponent.visitTree(UIComponent.java:1468)
at com.sun.faces.context.PartialViewContextImpl.processComponents(PartialViewContextImpl.java:400)
at com.sun.faces.context.PartialViewContextImpl.processPartial(PartialViewContextImpl.java:319)
at org.primefaces.context.PrimePartialViewContext.processPartial(PrimePartialViewContext.java:63)
at javax.faces.context.PartialViewContextWrapper.processPartial(PartialViewContextWrapper.java:228)
at org.omnifaces.context.OmniPartialViewContext.processPartial(OmniPartialViewContext.java:122)
at javax.faces.component.UIViewRoot.encodeChildren(UIViewRoot.java:1101)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1647)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:442)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:170)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at org.omnifaces.viewhandler.OmniViewHandler.renderView(OmniViewHandler.java:115)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:102)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:76)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:199)
at javax.faces.webapp.FacesServlet.executeLifecyle(FacesServlet.java:708)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:451)
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:74)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129)
at org.omnifaces.filter.GzipResponseFilter.doFilter(GzipResponseFilter.java:181)
at org.omnifaces.filter.HttpFilter.doFilter(HttpFilter.java:108)
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at com.github.adminfaces.template.session.AdminFilter.doFilter(AdminFilter.java:128)
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at io.opentracing.contrib.jaxrs2.server.SpanFinishingFilter.doFilter(SpanFinishingFilter.java:55)
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84)
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
at io.undertow.servlet.handlers.ServletChain.handleRequest(ServletChain.java:68)
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:132)
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
at io.undertow.server.handlers.DisableCacheHandler.handleRequest(DisableCacheHandler.java:33)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.security.handlers.AuthenticationConstraintHandler.handleRequest(AuthenticationConstraintHandler.java:53)
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
at io.undertow.servlet.handlers.security.ServletSecurityConstraintHandler.handleRequest(ServletSecurityConstraintHandler.java:59)
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jaspi.JASPICSecureResponseHandler.handleRequest(JASPICSecureResponseHandler.java:48)
at org.wildfly.extension.undertow.deployment.GlobalRequestControllerHandler.handleRequest(GlobalRequestControllerHandler.java:68)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292)
at io.undertow.servlet.handlers.ServletInitialHandler.access0(ServletInitialHandler.java:81)
at io.undertow.servlet.handlers.ServletInitialHandler.call(ServletInitialHandler.java:138)
at io.undertow.servlet.handlers.ServletInitialHandler.call(ServletInitialHandler.java:135)
at io.undertow.servlet.core.ServletRequestContextThreadSetupAction.call(ServletRequestContextThreadSetupAction.java:48)
at io.undertow.servlet.core.ContextClassLoaderSetupAction.call(ContextClassLoaderSetupAction.java:43)
at org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction.lambda$create[=12=](SecurityContextThreadSetupAction.java:105)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create[=12=](UndertowDeploymentInfoService.java:1502)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create[=12=](UndertowDeploymentInfoService.java:1502)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create[=12=](UndertowDeploymentInfoService.java:1502)
at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create[=12=](UndertowDeploymentInfoService.java:1502)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272)
at io.undertow.servlet.handlers.ServletInitialHandler.access[=12=]0(ServletInitialHandler.java:81)
at io.undertow.servlet.handlers.ServletInitialHandler.handleRequest(ServletInitialHandler.java:104)
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:364)
at io.undertow.server.HttpServerExchange.run(HttpServerExchange.java:830)
at org.jboss.threads.ContextClassLoaderSavingRunnable.run(ContextClassLoaderSavingRunnable.java:35)
at org.jboss.threads.EnhancedQueueExecutor.safeRun(EnhancedQueueExecutor.java:1982)
at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.doRunTask(EnhancedQueueExecutor.java:1486)
at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1377)
at java.lang.Thread.run(Unknown Source)
其他任何东西都没有问题，因为当我删除 value="#{questionMB.tags}" 时它完全可以正常工作，所以我可以删除、添加和搜索标签。但是当我添加值时：我输入一个字符（DBHelper.completeTag() 仍然可以正常工作，而 returns 值只是没有显示在 UI 中）并且抛出异常。
所以问题似乎是无法生成转换器（请参阅堆栈跟踪中的第 2 行）。所以我认为转换它应该没问题，因为我只使用字符串。可能列表有问题，无法转换。所以我找了两天也没找到一个可以回答我的问题。
编辑
我已经测试了哪些组件为空：DBHelper.completeTag() returns 一个很好的字符串列表，其中包含来自数据库的正确值。 List<String> tags = new ArrayList<>(); 初始化标签列表但没有字符串值（非空）。
我正在使用 Primefaces 7.0、OmniFaces 3.2、Mojarra 和 Primefaces-Extensions 6.1.1。
@Kukeltje 发现，这是一个已知问题：NPE when determining converter for primitive values。
据说解决方法是installing omnifaces 3.3。
实际修复计划在 Mojarra 2.3.10 版本 - Jakarta Faces 的参考实现中进行。
昨天我在评论中建议有人应该写 this 答案但是评论被删除了，所以我在这里尽管这不是我的发现。随意写另一个答案，这不是为了获得声誉，而是为其他遇到此问题的人提供路标。虽然疯狂地没有人对删除的评论有任何反馈，但我猜它被删除是因为我暗示 OP 肯定没有以讽刺的方式使用 Mojarra 的第 8 版。如果有人觉得被冒犯了，抱歉。