如果我有两个以上的实体，我是否需要在 Java Spring 中声明一个 entitymanagerfactory？答案

【问题标题】：Do i need to declare an entitymanagerfactory in Java Spring if i have more than two Entities?如果我有两个以上的实体，我是否需要在 Java Spring 中声明一个 entitymanagerfactory？
【发布时间】：2026-01-21 01:05:02
【问题描述】：

在将我的 2 个数据库表拆分为更符合逻辑的表后，我最终得到了 6 个表，这些表是我在 Java 中作为实体实现的。

由于我实现了它们，因此在部署 Spring 应用程序时出现 NullPointerException。

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-10-17 16:41:35.924 ERROR 8012 --- [  restartedMain] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]: Invocation of init method failed; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1804) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:620) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1154) ~[spring-context-5.3.10.jar:5.3.10]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:908) ~[spring-context-5.3.10.jar:5.3.10]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.10.jar:5.3.10]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.5.5.jar:2.5.5]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754) ~[spring-boot-2.5.5.jar:2.5.5]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:434) ~[spring-boot-2.5.5.jar:2.5.5]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:338) ~[spring-boot-2.5.5.jar:2.5.5]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1343) ~[spring-boot-2.5.5.jar:2.5.5]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1332) ~[spring-boot-2.5.5.jar:2.5.5]
    at com.softwareprojekt.explorer.ExplorerApplication.main(ExplorerApplication.java:10) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) ~[spring-boot-devtools-2.5.5.jar:2.5.5]
Caused by: java.lang.NullPointerException: null
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processFkSecondPassesInOrder(InFlightMetadataCollectorImpl.java:1745) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processSecondPasses(InFlightMetadataCollectorImpl.java:1655) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:295) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.metadata(EntityManagerFactoryBuilderImpl.java:1224) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:1255) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:58) ~[spring-orm-5.3.10.jar:5.3.10]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) ~[spring-orm-5.3.10.jar:5.3.10]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:409) ~[spring-orm-5.3.10.jar:5.3.10]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:396) ~[spring-orm-5.3.10.jar:5.3.10]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341) ~[spring-orm-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1863) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1800) ~[spring-beans-5.3.10.jar:5.3.10]
    ... 21 common frames omitted


Process finished with exit code 0

如果我有多个表，是否必须实现数据访问对象？如果是，我该如何在春天做到这一点？据我所知，Spring 都是在内部完成的。

这些是我的一些实体 1.

@Entity
@Table(name="account")
public class Account implements Serializable{

@Id
private String address;

private String authentication_key;

private int sequence_number;

private boolean is_frozen;

@Entity
@Table(name="accountbalancexdx")
public class AccountBalanceXDX implements Serializable{

@Id
private String address;

private double amount;

@Entity
@Table(name="accountbalancexus")
public class AccountBalanceXUS implements Serializable{
@Id
@OneToOne
private String address;

private double amount;

目前还没有控制器或存储库。

编辑：我刚刚发现在使用 @OneToOne 之类的 ORM 注释时出现错误。那么在Spring中，你不能使用这些注解吗？

非常感谢每一条有用的信息。

【问题讨论】：

你当然可以在 Spring 中使用 ORM 注释。您应该显示整个错误消息，以便我们知道问题可能是什么。
1.告诉我们您阅读了哪些文档或完成了哪些教程。 2. 如果有异常，请发布整个异常堆栈跟踪，因为小块不显示任何您的情况。
好的，我更新了错误消息。我在 Youtube 上观看了 Java Brains 的 Full Stack 课程，以及关于 ORM 但使用 Java EE 的大学课程。我以为我可以将它们两者结合起来，但我从未在 Spring 应用程序中手动实现持久性单元。所以我试图避免它，因为我也不知道如何将存储库与持久性单元结合起来。

标签： java spring spring-boot hibernate hibernate-entitymanager

【解决方案1】：

这里使用@OneToOne 是不正确的：

@Id
@OneToOne
private String address;

@OneToOne 用于实体，String 不是实体。所以你需要删除那个注释

【讨论】：

【解决方案2】：

基本上@OneToOne、@ManyToOne 等通常用于在实体类中定义外键关系。话虽如此，这两个注释中的任何一个都应该采用实体而不是 String、Long 等。

Baeldung 描述的类似这样的东西：您的主表：

@Entity 
@Table(name = "users") 
 public class User {
    
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Long id;
    //... 

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "address_id", referencedColumnName = "id")
    private Address address;

    // ... getters and setters 
 }

您的孩子/次要餐桌

@Entity
@Table(name = "address")
public class Address {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Long id;
    //...

    @OneToOne(mappedBy = "address")
    private User user;

    //... getters and setters
}

更多信息可以找到here

【讨论】：