java - 我得到 java.lang.NullPointerException : null when I try to initialize the method in Vaadin View

Question

我正在学习Java Spring。当我尝试使用方法从数据库获取数据时，出现以下错误:

java.lang.NullPointerException: null
    at com.exam.kino.repository.SeansRepository.findAll(SeansRepository.java:59) ~[classes/:na]
    at com.exam.kino.views.ChoseNumberOfTicketsView.<init>(ChoseNumberOfTicketsView.java:56) ~[classes/:na]
    at com.exam.kino.views.KinoUI.init(KinoUI.java:18) ~[classes/:na]
    at com.vaadin.ui.UI.doInit(UI.java:776) ~[vaadin-server-8.8.3.jar:8.8.3]
    at com.vaadin.server.communication.UIInitHandler.getBrowserDetailsUI(UIInitHandler.java:218) [vaadin-server-8.8.3.jar:8.8.3]
    at com.vaadin.server.communication.UIInitHandler.synchronizedHandleRequest(UIInitHandler.java:76) [vaadin-server-8.8.3.jar:8.8.3]
    at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40) [vaadin-server-8.8.3.jar:8.8.3]
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1602) [vaadin-server-8.8.3.jar:8.8.3]
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:445) [vaadin-server-8.8.3.jar:8.8.3]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:352) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.springframework.web.servlet.mvc.ServletForwardingController.handleRequestInternal(ServletForwardingController.java:141) [spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:177) [spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:52) [spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1039) [spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) [spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) [spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:908) [spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) [spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) [tomcat-embed-websocket-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:109) [spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) [spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:109) [spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) [spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:109) [spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) [spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:109) [spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:853) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1587) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_201]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_201]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.21.jar:9.0.21]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_201]

我的方法是在负责Vaadin的View的类中调用的。当他们尝试在主类中调用它进行测试时，一切正常。这是我在 Repository 类中的方法，我的问题是关于 findAll 类:

@Repository
public class SeansRepository {

    @Autowired
    JdbcTemplate jdbcTemplate;

    public Seans findById(long id) {

        return jdbcTemplate.queryForObject("select * from seans where id=? ", new Object[] { id },
                new BeanPropertyRowMapper<Seans>(Seans.class));

    }

    public Collection<Seans> findAll() {

        Collection<Seans> seans = (Collection<Seans>) jdbcTemplate.query("select * from seans", new BeanPropertyRowMapper(Seans.class));
        return seans;
    }

    public int deleteById(long id) {
        return jdbcTemplate.update("delete from seans where id=?", new Object[] { id });
    }
}

这是在 View 类中调用方法的方式:

@DesignRoot
@AutoGenerated
@SuppressWarnings("serial")
public class ChoseNumberOfTicketsView extends AbsoluteLayout implements View{
    protected TextField nameTextField;
    protected TextField surnameTextField;
    protected Label menuLabel;
    protected TextField emailTextField;
    protected TextField dticketsTextField;
    protected TextField nticketsTextField;
    protected ComboBox<Seans> movieComboBox;
    private SeansRepository repository;

    public ChoseNumberOfTicketsView() {
        Design.read(this);  
        repository = new SeansRepository();
        movieComboBox = new ComboBox<>("Chose the movie");
        movieComboBox.setItems(repository.findAll());

    }
}

我正在尝试获取电影列表并将其放入 ComboBox 中以供选择。

我正在添加一个 UI 类，其中包含我的 View 实例:

@SpringUI
public class KinoUI extends UI{
    Navigator navigator;

    @Override
    protected void init(VaadinRequest request) {
        getPage().setTitle("Exam");
        navigator = new Navigator(this, this);
        navigator.addView("", new StartView());
        navigator.addView("chosenumberoftickets",  new ChoseNumberOfTicketsView());
    }
}

Answer 1

感谢您添加查看代码。

问题在于您使用 new 关键字自行创建 SeasRepository。这样做，它不会由 Spring 管理，因此 Spring 不会 Autowiring 您的 JdbcTemplate。

相反，您还需要 Autowiring 您的 SeasRepository，试试这个

@Autowired
public ChoseNumberOfTicketsView(SeansRepository repository) {
    Design.read(this);  
    this.repository = repository;
    movieComboBox = new ComboBox<>("Chose the movie");
    movieComboBox.setItems(repository.findAll());

}