我正在尝试使程序在vaadin和spring-boot中工作，但无法使EntityManager工作。获取NullReferenceException
对于初学者来说，这是我的第一个尝试使用Spring-boot和Vaadin制作东西的方法。 我正在尝试使EntityManager正常工作，但出现了NullReferenceException。 看来我的EntityManager抛出了异常，但是我找不到任何有关如何正确使用它的示例。 我考虑过使用EntityManagerFactory，但同样，任何地方都没有示例。 findAll（）方法有效，所以我不确定该怎么办。
我有一个Repository_Room接口
public interface Repository_Room
{
void save(Room room);
void delete(Room room);
void update(Room room);
List<Room> findAll();
List<Course> getCourses(Room room);
}
在Repository_Room_Impl类中实现
@Transactional
@Repository
public class Repository_Room_Impl implements Repository_Room{
@PersistenceContext
private EntityManager em;
public Repository_Room_Impl()
{
}
@Override
public List<Room> findAll() {
return em.createQuery("select n from " + Room.class.getSimpleName() + " n").getResultList();
}
@Override
public void save(Room room) {
em.persist(room);
}
public void delete(Room room) {
em.remove(em.find(Room.class, room.getId()));
}
public void update(Room room) {
em.merge(em);
}
public List<Course> getCourses(Room room)
{
List<Course> courses = em.createQuery("select n from " + Course.class.getSimpleName() + " n WHERE n.Room = :roomID", Course.class)
.setParameter("roomID", room.getId())
.getResultList();
return courses;
}
}
尝试使用表单中的存储库添加新元素
@SpringComponent
@UIScope
public class Form_Room extends VerticalLayout {
private Room room;
private Reloader reloader;
private TextField val_id;
private TextField val_name;
private TextField val_level;
private Binder<Room> binder;
@Autowired
private Repository_Room repository;
public Form_Room()
{
binder = new Binder<>(Room.class);
val_id = new TextField("ID:");
val_name = new TextField("Name:");
val_level = new TextField(("Level:"));
binder.forField(val_id)
.withConverter(
new StringToIntegerConverter("Must enter a number"))
.bind(Room::getId, Room::setId);
binder.forField(val_name).bind(Room::getName, Room::setName);
binder.forField(val_level)
.withConverter(
new StringToIntegerConverter("Must enter a number"))
.bind(Room::getLevel, Room::setLevel);
add(val_id);
add(val_name);
add(val_level);
}
public Room getRoom() {
return room;
}
public void setRoom(Room room) {
if (room == null) {
this.room = null;
}
else {
this.room = room;
binder.readBean(this.room);
}
}
public Reloader getReloader() {
return reloader;
}
public void setReloader(Reloader reloader) {
this.reloader = reloader;
}
public void updateRoom()
{
try
{
if(room == null)
{
repository.save(this.room);
System.out.println("Created");
}
else
{
binder.writeBean(this.room);
repository.update(this.room);
System.out.println("Updated");
}
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
此表单是在我看来创建的
@Route(value = "rooms")
public class View_CRUD_Room extends VerticalLayout implements Reloader{
@Autowired
private Repository_Room repository;
@Autowired
private Form_Room form;
private Grid<Room> grid;
private Button button_view;
private Button button_remove;
private Button button_execute;
private HorizontalLayout buttonLayout;
private Room selected;
@PostConstruct
private void init(){
form = new Form_Room();
grid = new Grid<>();
button_view = new Button();
button_remove = new Button();
buttonLayout = new HorizontalLayout();
selected = null;
button_execute = new Button();
button_execute.setText("Végrehajt");
button_view.setText("Részletek");
button_remove.setText("Töröl");
buttonLayout.add(button_view);
buttonLayout.add(button_remove);
form.setVisible(true);
button_execute.addClickListener(event -> {
form.updateRoom();
});
button_view.addClickListener(event -> {
// Display details
});
button_remove.addClickListener(event -> {
// Display form with confirmation message and YesNo buttons
});
List<Room> list = repository.findAll();
grid.setItems(repository.findAll());
grid.addColumn(Room::getId).setHeader("Id");
grid.addColumn(Room::getName).setHeader("Name");
grid.addColumn(Room::getLevel).setHeader("Terem");
grid.asSingleSelect().addValueChangeListener(selectionEvent -> {
if (selectionEvent.getValue() != null) {
selected = selectionEvent.getValue();
form.setRoom(selected);
} else {
selected = null;
form.setRoom(selected);
}
});
add(new Text("Termek"));
add(grid);
add(buttonLayout);
add(form);
add(button_execute);
}
@Override
public void processRefresh() {
grid.setItems(repository.findAll());
}
}
stackTrace打印以下内容：
java.lang.NullPointerException
at com.example.beadando.repository.Impl.Repository_Room_Impl.save(Repository_Room_Impl.java:26)
at com.example.beadando.component.Form_Room.updateRoom(Form_Room.java:93)
at com.example.beadando.view.View_CRUD_Room.lambda$init$9b1b5227$1(View_CRUD_Room.java:55)
at com.vaadin.flow.component.ComponentEventBus.fireEventForListener(ComponentEventBus.java:205)
at com.vaadin.flow.component.ComponentEventBus.handleDomEvent(ComponentEventBus.java:373)
at com.vaadin.flow.component.ComponentEventBus.lambda$addDomTrigger$dd1b7957$1(ComponentEventBus.java:264)
at com.vaadin.flow.internal.nodefeature.ElementListenerMap.lambda$fireEvent$2(ElementListenerMap.java:420)
at java.util.ArrayList.forEach(ArrayList.java:1249)
at com.vaadin.flow.internal.nodefeature.ElementListenerMap.fireEvent(ElementListenerMap.java:420)
at com.vaadin.flow.server.communication.rpc.EventRpcHandler.handleNode(EventRpcHandler.java:59)
at com.vaadin.flow.server.communication.rpc.AbstractRpcInvocationHandler.handle(AbstractRpcInvocationHandler.java:64)
at com.vaadin.flow.server.communication.ServerRpcHandler.handleInvocationData(ServerRpcHandler.java:387)
at com.vaadin.flow.server.communication.ServerRpcHandler.lambda$handleInvocations$1(ServerRpcHandler.java:368)
at java.util.ArrayList.forEach(ArrayList.java:1249)
at com.vaadin.flow.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:368)
at com.vaadin.flow.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:310)
at com.vaadin.flow.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:89)
at com.vaadin.flow.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40)
at com.vaadin.flow.server.VaadinService.handleRequest(VaadinService.java:1507)
at com.vaadin.flow.server.VaadinServlet.service(VaadinServlet.java:242)
at com.vaadin.flow.spring.SpringServlet.service(SpringServlet.java:81)
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.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:352)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312)
at org.springframework.web.servlet.mvc.ServletForwardingController.handleRequestInternal(ServletForwardingController.java:141)
at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:177)
at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:52)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1039)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:908)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882)
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.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
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:200)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:836)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1747)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
我修改了setRoom（）方法以尝试添加一个新元素，而不必处理我的TextField。 尝试调用我的updateRoom（）方法时，以表格形式获取NullReferenceException。 请指出正确的方向。 谢谢！
答案 0 :(得分：1)
对不起，我以前看的时候太快了。
但这是您的问题，您是在自己创建自动装配的类，而不是让Spring为您创建它们。
@Autowired
private Repository_Room repository;
public Form_Room() {
repository = new Repository_Room_Impl(); //remove this line
//rest of the code
}
然后您在视图中再次执行此操作：
@Route(value = "rooms")
public class View_CRUD_Room extends VerticalLayout implements Reloader {
@PostConstruct
private void init(){
form = new Form_Room(); //remove this line
//rest of the code
}
您会看到自动装配称为“依赖注入”。这是一个很花哨的词，它说“框架”（在本例中为spring）将为您完成所有类的实例化。
Spring将为您完成“新任务”。并在运行时注入一个类供您使用，因此您不必这样做。 Spring还将在执行“ new RepositoryImpl（）”之前检查该类具有哪些依赖项，并查看它是否需要EntityManager，并为您自动实例化一个实例并将其放入RepositoryImpl。
这就是使用Autowire的全部要点，您不必执行新操作。您只需要相信使用时会在那里上课。
然后是关于代码的其他一些指针。
在Java中，我们使用驼峰式大小写，因此应该使用“驼峰式大小写”代替“ Repository_Room”，而对于“ Repository_Room_Impl”应该是“ RepositoryRoomImpl”