每当我将 @Component 添加到我的 Spring 程序时，启动都不会启动

Question

我是 Spring 新手，我一直在谈论 Spring Framework 5: Beginner to Guru 课程，每当我将 Componet 添加到我的代码中时，整个启动都不会启动 这个用于在数据库中存储书籍和作者姓名的简单代码

这是我的主线

package guru.springframework.spring5webapp;

import org.springframework.boot.SpringApplication; 
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication 
public class Spring5webappApplication {

    public static void main(String[] args) {
        SpringApplication.run(Spring5webappApplication.class, args);    
        }

}

这是我的数据库代码，我正在使用 h2

package guru.springframework.spring5webapp.bootstrap;

import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.stereotype.Component;
import guru.springframework.spring5webapp.domain.Author;
import guru.springframework.spring5webapp.domain.Book;
import guru.springframework.spring5webapp.repositories.AuthorRepository;
import guru.springframework.spring5webapp.repositories.BookRepository;

 @Component
 class DevBootstrap implements ApplicationListener<ContextRefreshedEvent> {

    private AuthorRepository authorRepository;
    private BookRepository bookRepositroy;

    public DevBootstrap(AuthorRepository authorRepository, BookRepository bookRepositroy) {
        super();
        this.authorRepository = authorRepository;
        this.bookRepositroy = bookRepositroy;
    }
    @Override
    public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
        initdata();

    }
    private void initdata() {

        //Mostafa
        Author Mostafa = new Author("Mostafa", "Desoky");
        Book Farm = new Book("How to farm101","135","Feeders");
        Mostafa.getBooks().add(Farm);
        Farm.getAuthors().add(Mostafa);
        authorRepository.save(Mostafa);
        bookRepositroy.save(Farm);

        //Mahmoud
        Author Mahmoud = new Author("Mahmoud", "Ragab");
        Book  EM = new Book("El3ol2ya mas2olya", "22485", "ElGomhorya");
        Mahmoud.getBooks().add(EM);
        EM.getAuthors().add(Mahmoud);
        authorRepository.save(Mahmoud);
        bookRepositroy.save(EM);

    }

}

我的作者代码

package guru.springframework.spring5webapp.domain;

import javax.persistence.*;
import java.util.Set;


@Entity
public class Author {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String firstName;
    private String lastName;

    @ManyToMany(mappedBy = "authors")
    private Set<Book> books;



    public Author(String firstName, String lastName) {
        super();
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public Author(String firstName, String lastName, Set<Book> books) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.books = books;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public Set<Book> getBooks() {
        return books;
    }

    public void setBooks(Set<Book> books) {
        this.books = books;
    }

    @Override
    public String toString() {
        return "Author [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", books=" + books + "]";
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Author other = (Author) obj;
        if (id == null) {
            if (other.id != null)
                return false;
        } else if (!id.equals(other.id))
            return false;
        return true;
    }

}

我的书码

package guru.springframework.spring5webapp.domain;

import javax.persistence.*;
import java.util.Set;

@Entity
public class Book {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String title;
    private String isbn;
    private String publisher;

    @ManyToMany
    @JoinTable(name = "author_book", joinColumns = @JoinColumn(name = "book_id"),
            inverseJoinColumns = @JoinColumn(name = "author_id"))
    private Set<Author> authors;


    public Book(String title , String isbn, String publisher) {
        super();
        this.publisher = publisher;
        this.title = title;
        this.isbn = isbn;
    }

    public Book(String title, String isbn,String publisher, Set<Author> authors) {
        this.publisher = publisher;
        this.title = title;
        this.isbn = isbn;
        this.authors = authors;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getIsbn() {
        return isbn;
    }

    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }


    public String getPublisher() {
        return publisher;
    }

    public void setPublisher(String publisher) {
        this.publisher = publisher;
    }

    public Set<Author> getAuthors() {
        return authors;
    }

    public void setAuthors(Set<Author> authors) {
        this.authors = authors;
    }

    @Override
    public String toString() {
        return "Book [id=" + id + ", title=" + title + ", isbn=" + isbn + ", publisher=" + publisher + ", authors="
                + authors + "]";
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Book other = (Book) obj;
        if (id == null) {
            if (other.id != null)
                return false;
        } else if (!id.equals(other.id))
            return false;
        return true;
    }

}

最后我的作者和书籍存储库扩展了 CrudRepository

package guru.springframework.spring5webapp.repositories;

import org.springframework.data.repository.CrudRepository;
import guru.springframework.spring5webapp.domain.Author;

public interface AuthorRepository extends CrudRepository<Author, Long> {

}

package guru.springframework.spring5webapp.repositories;

import org.springframework.data.repository.CrudRepository;
import guru.springframework.spring5webapp.domain.Book;

public interface BookRepository extends CrudRepository<Book, Long {

}

堆栈跟踪

spring5webapp - Spring5webappApplication [Spring Boot App]  
    guru.springframework.spring5webapp.Spring5webappApplication at localhost:59942  
        Thread [main] (Suspended (uncaught exception NullPointerException)) 
            ReflectionUtils.rethrowRuntimeException(Throwable) line: 142    
            SpringApplication.handleRunFailure(ConfigurableApplicationContext, Throwable, Collection<SpringBootExceptionReporter>, SpringApplicationRunListeners) line: 810 
            SpringApplication.run(String...) line: 325  
            SpringApplication.run(Class<?>[], String[]) line: 1226  
            SpringApplication.run(Class<?>, String...) line: 1215   
            Spring5webappApplication.main(String[]) line: 12    
    C:\Program Files\Java\jdk-13.0.1\bin\javaw.exe (Dec 26, 2019, 7:42:44 PM)   

Answer 1

问题是我必须在书籍和作者代码中初始化书籍和作者

private Set<Book> books = new HashSet<>();