Vaadin NPE ServerRpcHandler

本週我開始使用Vaadin，並從此給我留下了深刻的印象。但是，我遇到了一個我無法解決的問題。基本上，我做了一個Web應用程序，在其中顯示聯繫人（存儲在我的數據庫中）並將它們顯示在表格中。Vaadin NPE ServerRpcHandler

由於我使用Hibernate，我開始了與下面的代碼行：

JPAContainer<Contact>contactContainer = new JPAContainer<Contact>(Contact.class); 
    CachingMutableLocalEntityProvider<Contact> entityProvider = new CachingMutableLocalEntityProvider<Contact>(Contact.class, em); 
    contactContainer.setEntityProvider(entityProvider); 

    contactsList = new ContactsList(contactContainer);

正如你所看到的，我通過我的容器，一個叫ContactsList類所在的表等建：

table = new Table(); 
    table.setWidth(100, Unit.PERCENTAGE); 
    table.addStyleName(ValoTheme.TABLE_BORDERLESS); 
    table.addStyleName(ValoTheme.TABLE_COMPACT); 
    table.setSelectable(true); 
    table.setColumnCollapsingAllowed(true); 

    if(container != null) 
    { 
     table.setContainerDataSource(this.container); 
     table.setSortAscending(true); 
     table.setVisibleColumns("firstName", "lastName", "telephoneNr", "gsmNr", "creationDate"); 
     table.setColumnHeaders(SpringUtil.getMessage("label.contacts_firstname", null), 
           SpringUtil.getMessage("label.contacts_lastname", null), 
           SpringUtil.getMessage("label.contacts_telephone_nr", null), 
           SpringUtil.getMessage("label.contacts_gsm_nr", null), 
           SpringUtil.getMessage("label.contacts_creationdate", null)); 
    } 

    table.setMultiSelect(true); 
    table.setImmediate(true);

當我註釋掉所有代碼，我的應用程序運行完全沒有崩潰（ofcourse不顯示聯繫人表），但是當我嘗試編譯此代碼，調試時一切正常，該表已建成良好，即使之後，但那麼一個NPE被拋入0級上線：

if (invocation instanceof ServerRpcMethodInvocation) { 
    try { 
     ServerRpcManager.applyInvocation(connector, 
       (ServerRpcMethodInvocation) invocation); 
     } catch (RpcInvocationException e) { 
        manager.handleConnectorRelatedException(connector, e); 
     } 
} else {

完整的堆棧跟蹤如下所示：

SEVERE: java.lang.NullPointerException 
    at com.vaadin.addon.jpacontainer.provider.LocalEntityProvider.getEntityManager(LocalEntityProvider.java:215) 
    at com.vaadin.addon.jpacontainer.provider.LocalEntityProvider.doGetEntityManager(LocalEntityProvider.java:226) 
    at com.vaadin.addon.jpacontainer.provider.LocalEntityProvider.doGetEntityCount(LocalEntityProvider.java:510) 
    at com.vaadin.addon.jpacontainer.provider.CachingSupport$FilterCacheEntry.getEntityCount(CachingSupport.java:157) 
    at com.vaadin.addon.jpacontainer.provider.CachingSupport.getEntityCount(CachingSupport.java:826) 
    at com.vaadin.addon.jpacontainer.provider.CachingMutableLocalEntityProvider.getEntityCount(CachingMutableLocalEntityProvider.java:130) 
    at com.vaadin.addon.jpacontainer.JPAContainer.size(JPAContainer.java:912) 
    at com.vaadin.ui.AbstractSelect.size(AbstractSelect.java:762) 
    at com.vaadin.ui.Table.refreshRenderedCells(Table.java:1727) 
    at com.vaadin.ui.Table.attach(Table.java:4298) 
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) 
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577) 
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) 
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577) 
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) 
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577) 
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) 
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577) 
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) 
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577) 
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) 
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577) 
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) 
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577) 
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) 
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577) 
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) 
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577) 
    at com.vaadin.server.AbstractClientConnector.attach(AbstractClientConnector.java:590) 
    at com.vaadin.ui.AbstractComponent.attach(AbstractComponent.java:577) 
    at com.vaadin.ui.AbstractComponent.setParent(AbstractComponent.java:484) 
    at com.vaadin.ui.AbstractComponentContainer.addComponent(AbstractComponentContainer.java:210) 
    at com.vaadin.ui.CssLayout.addComponent(CssLayout.java:120) 
    at com.vaadin.navigator.Navigator$ComponentContainerViewDisplay.showView(Navigator.java:191) 
    at com.vaadin.navigator.Navigator.navigateTo(Navigator.java:568) 
    at com.vaadin.navigator.Navigator.navigateTo(Navigator.java:526) 
    at be.cematech.dashboard.ui.DashboardMenu$ValoMenuItemButton$1.buttonClick(DashboardMenu.java:167) 
    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:606) 
    at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:508) 
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:198) 
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:161) 
    at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:977) 
    at com.vaadin.ui.Button.fireClick(Button.java:387) 
    at com.vaadin.ui.Button$1.click(Button.java:55) 
    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:606) 
    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:168) 
    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:118) 
    at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:290) 
    at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:183) 
    at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:92) 
    at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41) 
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1404) 
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:305) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727) 
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303) 
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) 
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) 
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) 
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) 
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220) 
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122) 
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503) 
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170) 
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) 
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950) 
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) 
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421) 
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070) 
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611) 
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316) 
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) 
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) 
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) 
    at java.lang.Thread.run(Thread.java:745)

UPDATE

可能是什麼需要了解的是，我用這個ContactList不同的頁面上以及我在哪裏有相同的代碼行，但它能夠顯示錶格。這是否有兩個EntityManagers和/或EntityProviders訪問相同的數據？

UPDATE2

@PersistenceContext 
protected EntityManager em;

來源

2014-11-01 RazorAlliance192

第二次EntityManager爲空......有人可以幫我弄清楚如何解決這個問題？ – RazorAlliance192 2014-11-01 18:46:44

實際上只是在您的代碼中傳入您的EntityManager。你如何創建/回顧它？ – MarcelloGarini 2014-11-03 08:09:50

我把它聲明在我的類文件的頂部（參見UPDATE2） – RazorAlliance192 2014-11-03 08:47:09

按UPDATE2我看見你retrive在運行時用註釋「@PersistenceContext」你的EntityManager。如果您在「CDI bean，EJB，Servlet，Servlet監聽器，Servlet過濾器或JSF ManagedBean」中使用它，則可以解決這個問題。（http://tomee.apache.org/examples-trunk/injection-of-entitymanager/README.html）我的猜測是，在「其他頁面」上，您處於正確的上下文環境註釋是有效的，而在「這個」頁面中則不是。檢查這一點，如果是這種情況我建議你手動實例EntityManager的使用例如

JPAContainerFactory.make(Contact.class, "PERSISTENCE_UNIT_NAME");

，如果您有/在項目中使用persistence.xml文件。否則，一個辦法是創建自定義喜歡

Persistence.createEntityManagerFactory("persistence_unit_name", properties).createEntityManager()

，其屬性的EntityManagerFactory的是一個Map的持久性的像

Map<String, String> properties = new HashMap<String, String>(); 
properties.put(JDBC_DRIVER, this.jdbcDriver); 
properties.put(JDBC_URL, this.url); 
properties.put(JDBC_USER, this.username); 
properties.put(JDBC_PASSWORD, this.password); 

// Configure logging. FINE ensures all SQL is shown 
properties.put(LOGGING_LEVEL, "FINE"); 
return properties;

的EntityManager像這樣的振作的是，你可以把它隨時爲您待命在你的應用程序。乾杯。

來源

2014-11-03 09:11:58 MarcelloGarini

Vaadin NPE ServerRpcHandler

回答

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