spring - 无法调用 "java.lang.Object.hashCode()"，因为 "value"为空-6ren

spring - 无法调用 "java.lang.Object.hashCode()"，因为 "value"为空

转载作者：行者123 更新时间：2023-12-05 03:37:49

在 spring 应用中:

用户.java:

@Entity
@Data
@NoArgsConstructor
public class User {
    @Id @GeneratedValue
    private Long id;
    @Column(unique = true)
    private String username;
    private String about;
    @OneToMany(mappedBy = "owner", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @MapKey(name = "friendId")
    private Map<User, Friendship> friendships = new HashMap<>();
    @OneToMany(mappedBy = "author", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @MapKey(name = "title")
    private Map<String, Post> posts = new HashMap<>();

    public User(String username) {
        this.username = username;
    }
    public User addFriend(User friend){
        Friendship friendship = new Friendship();
        friendship.setOwner(this);
        friendship.setFriend(friend);

        friend.getFriendships().put(this, friendship);
        getFriendships().put(friend, friendship);
        return friend;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof User)) return false;
        User user = (User) o;
        return this.username.equals(user.getUsername());
    }

    @Override
    public int hashCode() {
        return this.username.hashCode();
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", about='" + about + '\'' +
                ", posts=" + posts +
                '}';
    }
}

友谊.java:

@IdClass(Friendship.class)
@Entity
@Data
public class Friendship implements Serializable {
    @Id @Column(name = "owner_id")
    private Long ownerId;
    @Id @Column(name = "friend_id")
    private Long friendId;
    @ManyToOne @MapsId("owner_id")
    private User owner;
    @ManyToOne @MapsId("friend_id")
    private User friend;
    private String level;
}

演示应用程序:

@Bean
    public CommandLineRunner loadData(UserRepository userRepo){
        return new CommandLineRunner() {
            @Override
            public void run(String... args) throws Exception {
                User owner = new User("Barta");
                User martin = owner.addFriend(new User("Martin"));
                User milan = owner.addFriend(new User("Milan"));
                userRepo.save(owner);
            }
        };
    }

运行时，错误是 Cannot invoke "java.lang.Object.hashCode()"because "value"is null 我想 "value"是 username。但是用户名是在构造函数中设置的(我什至在调试中也能看到)，为什么我会得到 NullPointerException？

附言:

完整的错误堆栈:

java.lang.IllegalStateException: Failed to execute CommandLineRunner
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:794) ~[spring-boot-2.5.3.jar:2.5.3]
    at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:775) ~[spring-boot-2.5.3.jar:2.5.3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:345) ~[spring-boot-2.5.3.jar:2.5.3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1343) ~[spring-boot-2.5.3.jar:2.5.3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1332) ~[spring-boot-2.5.3.jar:2.5.3]
    at com.example.demo.DemoApplication.main(DemoApplication.java:16) ~[classes/:na]
Caused by: java.lang.NullPointerException: Cannot invoke "java.lang.Object.hashCode()" because "value" is null
    at org.hibernate.type.descriptor.java.AbstractTypeDescriptor.extractHashCode(AbstractTypeDescriptor.java:78) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.type.AbstractStandardBasicType.getHashCode(AbstractStandardBasicType.java:200) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.type.AbstractStandardBasicType.getHashCode(AbstractStandardBasicType.java:205) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.type.EntityType.getHashCode(EntityType.java:383) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.type.ComponentType.getHashCode(ComponentType.java:249) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.spi.EntityKey.generateHashCode(EntityKey.java:61) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.spi.EntityKey.<init>(EntityKey.java:54) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.internal.AbstractSharedSessionContract.generateEntityKey(AbstractSharedSessionContract.java:536) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:172) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:135) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:185) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:128) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.internal.SessionImpl$$Lambda$1219/0x00000000a219d8f8.applyEventToListener(Unknown Source) ~[na:na]
    at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:110) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:744) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:712) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.spi.CascadingActions$7.cascade(CascadingActions.java:298) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:499) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:423) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:220) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:532) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:463) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:426) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:220) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:153) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:459) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:293) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:193) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:135) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:185) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:128) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:55) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.internal.SessionImpl$$Lambda$1218/0x00000000a21505e0.accept(Unknown Source) ~[na:na]
    at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:99) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:720) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:706) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:567) ~[na:na]
    at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:311) ~[spring-orm-5.3.9.jar:5.3.9]
    at jdk.proxy2/jdk.proxy2.$Proxy98.persist(Unknown Source) ~[na:na]
    at org.springframework.data.jpa.repository.support.SimpleJpaRepository.save(SimpleJpaRepository.java:597) ~[spring-data-jpa-2.5.3.jar:2.5.3]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:567) ~[na:na]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker$RepositoryFragmentMethodInvoker.lambda$new$0(RepositoryMethodInvoker.java:289) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker$RepositoryFragmentMethodInvoker$$Lambda$1217/0x00000000a214e200.invoke(Unknown Source) ~[na:na]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker.doInvoke(RepositoryMethodInvoker.java:137) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.RepositoryMethodInvoker.invoke(RepositoryMethodInvoker.java:121) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.RepositoryComposition$RepositoryFragments.invoke(RepositoryComposition.java:529) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.RepositoryComposition.invoke(RepositoryComposition.java:285) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$ImplementationMethodExecutionInterceptor.invoke(RepositoryFactorySupport.java:599) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.doInvoke(QueryExecutorMethodInterceptor.java:163) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.invoke(QueryExecutorMethodInterceptor.java:138) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:80) ~[spring-data-commons-2.5.3.jar:2.5.3]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:123) ~[spring-tx-5.3.9.jar:5.3.9]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:388) ~[spring-tx-5.3.9.jar:5.3.9]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:119) ~[spring-tx-5.3.9.jar:5.3.9]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:137) ~[spring-tx-5.3.9.jar:5.3.9]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:174) ~[spring-data-jpa-2.5.3.jar:2.5.3]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215) ~[spring-aop-5.3.9.jar:5.3.9]
    at jdk.proxy2/jdk.proxy2.$Proxy103.save(Unknown Source) ~[na:na]
    at com.example.demo.DemoApplication$1.run(DemoApplication.java:27) ~[classes/:na]
    at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:791) ~[spring-boot-2.5.3.jar:2.5.3]
    ... 5 common frames omitted

2021-09-13 15:55:23.677  INFO 3218 --- [           main] j.LocalContainerEntityManagerFactoryBean : Closing JPA EntityManagerFactory for persistence unit 'default'
2021-09-13 15:55:23.682  INFO 3218 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2021-09-13 15:55:23.694  INFO 3218 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.

Process finished with exit code

附言:

intellij 正在标记

@MapKey(name = "friendId")

有错误:

'java.lang.Long' cannot be assigned to 'com.example.demo.model.User'

正如我试图理解的那样 -> 在创建时将 id 分配为 null，这是期望的。因此，为 id 分配值(主键)的唯一方法是在持久化时(否则我不知道，当使用 @GenerateValue 时，JPA 何时将值分配给主键)

最佳答案

大多数时候我会在 @Entity 中使用 equals 和 hashCode 的 id

 @Override
public boolean equals(Object o)
{
    if (this == o)
    {
        return true;
    }
    if (o == null || getClass() != o.getClass())
    {
        return false;
    }
    User user = (User) o;
    return Objects.equals(id, disclaimer.id);
}

@Override
public int hashCode()
{
    return Objects.hash(id);
}

如果你真的有理由将名称作为键，我建议你阅读一些关于@NaturalId 的内容并将 hashCode 方法设为 null 保存

@Override
public int hashCode()
{
    return Objects.hash(name);
}

关于spring - 无法调用 "java.lang.Object.hashCode()"，因为 "value"为空，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/69155143/

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spring - 无法调用 "java.lang.Object.hashCode()"，因为 "value"为空