java - 我无法在 Vaadin 组件中调用 JpaRepository api

Question

我是 Vaadin 和 Spring Boot 的新手，我正在尝试制作一个可以执行所有 CRUD 方法的小应用程序。我正在制作这个表单，它将接收字段中的所有数据，将其保存到模型对象并将其保存到我的数据库中，但它不允许我这样做。

StudentRepo

package com.vinh.vaadin.allinone.repo;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import com.vinh.vaadin.allinone.entity.Student;
@Repository
public interface StudentRepo extends JpaRepository<Student, Long>{
}

学生表格

package com.vinh.vaadin.allinone.vaadin;

import org.springframework.beans.factory.annotation.Autowired;

import com.vaadin.data.Binder;
import com.vaadin.data.ValidationException;
import com.vaadin.spring.annotation.SpringComponent;
import com.vaadin.ui.Button;
import com.vaadin.ui.FormLayout;
import com.vaadin.ui.HorizontalLayout;
import com.vaadin.ui.TextField;
import com.vinh.vaadin.allinone.entity.Student;
import com.vinh.vaadin.allinone.repo.StudentRepo;

@SpringComponent
public class StudentForm extends FormLayout{
    @Autowired
    StudentRepo repo;
    Student student = new Student();

    private TextField firstName = new TextField("First Name");
    private TextField lastName = new TextField("Last Name");
    private TextField email = new TextField("Email");
    private Button save = new Button("Save");
    private Button delete = new Button("Delete");
    private Binder<Student> binder = new Binder<>(Student.class);



    public StudentForm() {
        HorizontalLayout buttons = new HorizontalLayout(save, delete);
        addComponents(firstName, lastName, email, buttons);

        binder.bindInstanceFields(this);
        binder.setBean(student);
        setSizeUndefined();

        save.addClickListener(event -> {
            try {
                binder.writeBean(student);
            } catch (ValidationException e) {
                e.printStackTrace();
            } finally {
                saveStudent(student);
            }
        });
    }

    private void saveStudent(Student theStudent) {
        repo.save(theStudent);
    }

}

StudentForm 被调用的主要内容

package com.vinh.vaadin.allinone.vaadin;

import java.util.ArrayList;
import java.util.List;

import javax.annotation.PostConstruct;

import org.assertj.core.util.Lists;
import org.springframework.beans.factory.annotation.Autowired;

import com.vaadin.icons.VaadinIcons;
import com.vaadin.spring.annotation.SpringComponent;
import com.vaadin.ui.Alignment;
import com.vaadin.ui.Button;
import com.vaadin.ui.CssLayout;
import com.vaadin.ui.Grid;
import com.vaadin.ui.HorizontalLayout;
import com.vaadin.ui.TextField;
import com.vaadin.ui.VerticalLayout;
import com.vaadin.ui.themes.ValoTheme;
import com.vinh.vaadin.allinone.entity.Student;
import com.vinh.vaadin.allinone.repo.StudentRepo;

import javassist.expr.NewArray;

@SpringComponent
public class MainContent extends VerticalLayout {
    @Autowired
    private Student student;
    @Autowired
    StudentRepo repo;

    private StudentForm studentForm = new StudentForm();



    private CssLayout filterLayout;
    private TextField filterText;
    private Button filterBtn;
    private HomeUI homeUI;
    private Grid<Student> studentGrid;

    @PostConstruct
    void init() {
        setStudents(repo.findAll());
    }

    private void setStudents(List<Student> findAll) {
        studentGrid.setItems(findAll);
    }

    public MainContent() {
        addFilter();
        addMainContent();
    }

    private void addMainContent() {
        HorizontalLayout main = new HorizontalLayout();
        studentGrid = new Grid<>(Student.class);
        studentGrid.setColumns("firstName", "lastName", "email");
        main.addComponentsAndExpand(studentGrid);
        main.addComponents(studentForm);
        studentGrid.setSizeFull();
        addComponents(main);
    }

    private void addFilter() {
        filterLayout = new CssLayout();
        filterLayout.addStyleName(ValoTheme.LAYOUT_COMPONENT_GROUP);

        filterText = new TextField();
        filterText.setPlaceholder("filter by name...");

        filterBtn = new Button(VaadinIcons.CLOSE);

        filterLayout.addComponents(filterText, filterBtn);

        HorizontalLayout toolbar = new HorizontalLayout(filterLayout);
        addComponent(toolbar);
    }
}

总之，我有 MainContent 组件，它在左侧显示网格，然后在右侧显示 StudentForm。

一切都很好，直到我尝试在 StudentForm 中 repo.save(theStudent) ，并且出现此错误

java.lang.NullPointerException: null
    at com.vinh.vaadin.allinone.vaadin.StudentForm.lambda$0(StudentForm.java:44) ~[classes/:na]
    at sun.reflect.GeneratedMethodAccessor309.invoke(Unknown Source) ~[na:na]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_171]
    at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_171]
    at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:499) ~[vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:273) ~[vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:237) ~[vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.server.AbstractClientConnector.fireEvent(AbstractClientConnector.java:1014) ~[vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.ui.Button.fireClick(Button.java:384) ~[vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.ui.Button$1.click(Button.java:57) ~[vaadin-server-8.4.1.jar:8.4.1]
    at sun.reflect.GeneratedMethodAccessor308.invoke(Unknown Source) ~[na:na]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_171]
    at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_171]
    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:155) ~[vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.server.ServerRpcManager.applyInvocation(ServerRpcManager.java:116) ~[vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.server.communication.ServerRpcHandler.handleInvocation(ServerRpcHandler.java:445) [vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.server.communication.ServerRpcHandler.handleInvocations(ServerRpcHandler.java:410) [vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.server.communication.ServerRpcHandler.handleRpc(ServerRpcHandler.java:274) [vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:90) [vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40) [vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1601) [vaadin-server-8.4.1.jar:8.4.1]
    at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:445) [vaadin-server-8.4.1.jar:8.4.1]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1468) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [na:1.8.0_171]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [na:1.8.0_171]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at java.lang.Thread.run(Unknown Source) [na:1.8.0_171]

但是，如果我将 repo.save() 放入 MainContent 的 saveStudent() 方法中，则传递该 MainContent 到 StudentForm 然后从那里调用 saveStudent() 方法即可工作。为什么？

我的另一个问题是在 MainContent 中，如果我把它放在任何地方，我必须在 @PostConstruct 中添加 repo.findAll() 才能工作否则不是@PostConstruct，那么它就不起作用，这是为什么？

Answer 1

您的 StudentRepo 类应该使用 @Component 进行注释，因为您是在 StudentForm 类中创建它的 bean。

当创建 StudentForm 的 bean 时，它需要 StudentRepo 类的 bean，但该类未创建，因为您尚未将其标记为 @Component。因此，当您尝试访问 StudentRepo 的方法时，会抛出空指针异常

@Component
public interface StudentRepo extends JpaRepository<Student, Long> {
}

你还可以使用@Repository注解来指定这是一个dao层类。@Repository 扩展自@Component，仅用于保持命名一致。所以这两个注释都可以工作