【发布时间】：2021-01-28 17:46:45
【问题描述】：
我正在使用 Spring Data 从 mysql 数据库中提取和控制数据。我在将这些数据放入表格时遇到了问题。我正在使用 Vaadin 并遵循以下教程：
（但我正在努力适应我自己的目的）。本教程创建一个AbstractEntity，其他实体从该AbstractEntity 扩展。根据我的研究，这是某种形式的实体管理器，我相信它试图区分独特的实体。因为我只是想看看所有这些对象是如何组合在一起的，所以我决定只创建一个实体并从这个名为Stock 的AbstractEntity 扩展它。这个Stock类定义如下：
package com.stockmachine.v2.backend.entity;
import javax.persistence.*;
import javax.validation.constraints.Email;
import javax.validation.constraints.NotEmpty;
import javax.validation.constraints.NotNull;
@Entity
@Table (name="stock_info")
public class Stock extends AbstractEntity implements Cloneable {
@Id
private String Ticker;
private String Region;
public String getTicker() {
return Ticker;
}
public void setTicker(String ticker) {
Ticker = ticker;
}
public String getRegion() {
return Region;
}
public void setRegion(String region) {
Region = region;
}
}
这链接到我的 mysql 数据库中名为“stock_info”的表，该表有两个以上的列，但我只是在测试，所以我决定只为其中两个列创建变量，“Region”和“Ticker” .这只是一个包含股票代码列表的数据库，并包含一些关于它们的信息，其中一个信息是区域。
AbstractEntity 定义如下：
package com.stockmachine.v2.backend.entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.MappedSuperclass;
@MappedSuperclass
public abstract class AbstractEntity {
}
我还有如下StockService服务定义如下：
import com.stockmachine.v2.backend.entity.Stock;
import com.stockmachine.v2.backend.repository.StockRepository;
import org.springframework.stereotype.Service;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
@Service
public class StockService {
private static final Logger LOGGER = Logger.getLogger(StockService.class.getName());
private StockRepository stockRepository;
public StockService(StockRepository stockRepository) {
this.stockRepository = stockRepository;
}
public List<Stock> findAll() {
return stockRepository.findAll();
}
public long count() {
return stockRepository.count();
}
public void delete(Stock stock) {
stockRepository.delete(stock);
}
public void save(Stock stock) {
if (stock == null) {
LOGGER.log(Level.SEVERE,
"Contact is null. Are you sure you have connected your form to the application?");
return;
}
stockRepository.save(stock);
}
}
和存储库：
package com.stockmachine.v2.backend.repository;
import com.stockmachine.v2.backend.entity.Stock;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;
import java.util.List;
@Repository
public interface StockRepository extends JpaRepository<Stock, String> {
}
而主视图ui是：
package com.stockmachine.v2.ui;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.router.Route;
import com.stockmachine.v2.backend.entity.Stock;
import com.vaadin.flow.component.grid.Grid;
import com.stockmachine.v2.backend.service.StockService;
@Route("")
public class MainView extends VerticalLayout {
private StockService stockService;
private Grid<Stock> grid = new Grid<>(Stock.class);
public MainView(StockService stockService) {
addClassName("list-view");
setSizeFull();
configureGrid();
add(grid);
updateList();
}
private void configureGrid() {
grid.addClassName("stock-grid");
grid.setSizeFull();
grid.setColumns("ticker","region");
}
private void updateList() {
grid.setItems(stockService.findAll());
}
}
据我了解（可能完全错误），主视图将创建服务类StockService 的实例，该实例创建StockRepository 的实例，该实例从链接的Stock 类获取各种参数到@Table引用的数据库表。这会引发以下错误：
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.stockmachine.v2.ui.MainView': Bean instantiation via constructor failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.stockmachine.v2.ui.MainView]: Constructor threw exception; nested exception is java.lang.NullPointerException: Cannot invoke "com.stockmachine.v2.backend.service.StockService.findAll()" because "this.stockService" is null
at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:313) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:294) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1356) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1203) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:556) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:307) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at com.vaadin.flow.spring.SpringInstantiator.getOrCreate(SpringInstantiator.java:117) ~[vaadin-spring-12.3.2.jar:na]
at com.vaadin.flow.di.Instantiator.createRouteTarget(Instantiator.java:160) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.router.internal.AbstractNavigationStateRenderer.lambda$getRouteTarget$1(AbstractNavigationStateRenderer.java:135) ~[flow-server-2.4.3.jar:2.4.3]
at java.base/java.util.Optional.orElseGet(Optional.java:362) ~[na:na]
at com.vaadin.flow.router.internal.AbstractNavigationStateRenderer.getRouteTarget(AbstractNavigationStateRenderer.java:134) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.router.internal.AbstractNavigationStateRenderer.sendBeforeEnterEventAndPopulateChain(AbstractNavigationStateRenderer.java:518) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.router.internal.AbstractNavigationStateRenderer.createChainIfEmptyAndExecuteBeforeEnterNavigation(AbstractNavigationStateRenderer.java:498) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.router.internal.AbstractNavigationStateRenderer.handle(AbstractNavigationStateRenderer.java:230) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.router.Router.handleNavigation(Router.java:249) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.router.Router.navigate(Router.java:220) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.router.Router.navigate(Router.java:186) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.router.Router.initializeUI(Router.java:93) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.server.BootstrapHandler.createAndInitUI(BootstrapHandler.java:1526) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.server.BootstrapHandler.synchronizedHandleRequest(BootstrapHandler.java:475) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.server.VaadinService.handleRequest(VaadinService.java:1545) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.server.VaadinServlet.service(VaadinServlet.java:247) ~[flow-server-2.4.3.jar:2.4.3]
at com.vaadin.flow.spring.SpringServlet.service(SpringServlet.java:111) ~[vaadin-spring-12.3.2.jar:na]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.37.jar:4.0.FR]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:352) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.springframework.web.servlet.mvc.ServletForwardingController.handleRequestInternal(ServletForwardingController.java:141) ~[spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:177) ~[spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:52) ~[spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:626) ~[tomcat-embed-core-9.0.37.jar:4.0.FR]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.37.jar:4.0.FR]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130) ~[na:na]
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630) ~[na:na]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.37.jar:9.0.37]
at java.base/java.lang.Thread.run(Thread.java:832) ~[na:na]
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.stockmachine.v2.ui.MainView]: Constructor threw exception; nested exception is java.lang.NullPointerException: Cannot invoke "com.stockmachine.v2.backend.service.StockService.findAll()" because "this.stockService" is null
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:217) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:117) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:309) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
... 74 common frames omitted
Caused by: java.lang.NullPointerException: Cannot invoke "com.stockmachine.v2.backend.service.StockService.findAll()" because "this.stockService" is null
at com.stockmachine.v2.ui.MainView.updateList(MainView.java:31) ~[classes/:na]
at com.stockmachine.v2.ui.MainView.<init>(MainView.java:20) ~[classes/:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:64) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:na]
at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500) ~[na:na]
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:481) ~[na:na]
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:204) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
... 76 common frames omitted
2021-01-28 17:22:04.316 INFO 15528 --- [onPool-worker-5] dev-updater : No js modules to update 'D:\eclipse\StockMachineV2\target\frontend\generated-flow-imports.js' file
2021-01-28 17:22:49.207 ERROR 15528 --- [nio-8080-exec-7] c.v.flow.router.InternalServerError : There was an exception while trying to navigate to ''
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.stockmachine.v2.ui.MainView': Bean instantiation via constructor failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.stockmachine.v2.ui.MainView]: Constructor threw exception; nested exception is java.lang.NullPointerException: Cannot invoke "com.stockmachine.v2.backend.service.StockService.findAll()" because "this.stockService" is null
at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:313) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:294) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1356) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1203) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:556) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:307) ~[spring-beans-5.2.8.RELEASE.jar:5.2.8.RELEASE]
...
我假设this.stockService is null 表示该服务实际上并未从我的表中收集任何数据，因此返回为空。我不确定这是否与我删除实体管理器功能有关。我认为这只是服务的问题，但我无法解决。
考虑到代码有多少，我不希望任何人调试我的代码，但如果可能的话，请向我解释所有这些资源是如何通信的，以便我可以调试自己，因为我无法网上找一个清晰详细的解释。
提前感谢您的帮助:)
【问题讨论】：
-
但我正在努力适应我自己的目的 完成教程。了解它所教的内容...然后根据自己的目的调整内容。
-
@RiggsFolly 我已经完成了教程的数据库管理部分
标签： java mysql spring hibernate jpa