Working with Vaadin Navigator (NULL-Pointer Exception)

Vaadin 6 / 7 / 8
1

Hello,
id like to implement a custom Navigation.

At first, I would like to introduce you to the project structure.

MyUI.java

@Theme("Programmier_Test_theme")
public class MyUI extends UI {

    private static final long serialVersionUID = 1L;

    
    
    
    
    
    @Override
    protected void init(VaadinRequest vaadinRequest) {
    
        
        ViewLoginImpl viewlogin =new ViewLoginImpl();
        this.setContent(viewlogin);

In the Login -View i have to navigate to the Start-View.

@Override public void buttonClick(ClickEvent arg0) { LogIn.einloggen(); UI.getCurrent().getNavigator().addView(ViewStartImpl.ID,ViewStartImpl.class); UI.getCurrent().getNavigator().navigateTo(ViewStartImpl.ID); } // } all of my views implement the view interface!

after compiling I get the following error. (Click-Event)

[color=#e74c3c]
java.lang.NullPointerException
    at de.hftl.se.Vereinsapplikation_NIKA.view.login.ViewLoginImpl$1.buttonClick(ViewLoginImpl.java:92)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:510)
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:211)
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:174)
    at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:1033)
    at com.vaadin.ui.Button.fireClick(Button.java:370)
    at com.vaadin.ui.Button$1.click(Button.java:57)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:155)
    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:116)
    at com.vaadin.server.communication.ServerRpcHandler.handleInvocation(ServerRpcHandler.java:445)
    at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:410)
    at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:274)
    at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:90)
    at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1568)
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:381)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:475)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:651)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:500)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1376)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)

Dez 13, 2017 9:28:10 AM com.vaadin.server.DefaultErrorHandler doDefault
SCHWERWIEGEND: 
java.lang.NullPointerException
    at de.hftl.se.Vereinsapplikation_NIKA.presenter.MyUI.init(MyUI.java:48)
    at com.vaadin.ui.UI.doInit(UI.java:745)
    at com.vaadin.server.communication.UIInitHandler.getBrowserDetailsUI(UIInitHandler.java:216)
    at com.vaadin.server.communication.UIInitHandler.synchronizedHandleRequest(UIInitHandler.java:74)
    at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1568)
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:381)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:475)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:651)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:500)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1376)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)
[/color]
2

It’s a bit hard to interpret that from the code snippets alone, so a couple of questions to move things forward:

  • What happens on row 48 of MyUI.java, or row 92 of ViewLoginImpl.java? That’s where the NPE seems to originate from, but these line numbers obviously don’t match.
  • Do you get a null UI from the UI.getCurrent() (could happen if you try to use it from another thread), and have you created a Navigator for your UI at some point?
  • Which Vaadin version is this?
3

hello Anna,
thank you for your answer!

Point 1:

[code]

@Override
protected void init(VaadinRequest vaadinRequest) {

    
    ViewLoginImpl viewlogin =new ViewLoginImpl();
    this.setContent(viewlogin);
    


}       
@WebServlet(urlPatterns = "/*", name = "MyUIServlet", asyncSupported = true)

[/code]the bracket is row 48

public void buttonClick(ClickEvent arg0) { LogIn.einloggen(); UI.getCurrent().getNavigator().addView(ViewStartImpl.ID,ViewStartImpl.class); UI.getCurrent().getNavigator().navigateTo(ViewStartImpl.ID); } // } the first UI line reference row 92.

I only use the default Navigator from the UI class. I’d like to implement a custom navigator in the Start View.

I use Vaadin 8.

4

Hi,
You first need to set a Navigator before you can call it. If you call getNavigator() for a UI that does not have a navigator the result will be null (see:
https://vaadin.com/api/com/vaadin/ui/UI.html#getNavigator–
)

-Katri