为什么我得到JPQL NullPointerException以及如何解决它？

Question

我需要一个nullPointerException的帮助，当我在Dao上使用JPQL @Query时，我会得到帮助。我尝试了不同的选项，我似乎无法找到问题所在。 我在网上看到这是一个依赖问题，所以我更新了所有的依赖项，但我仍然得到相同的错误。我正在尝试使用带有@JoinColumn注释和ManyToOne映射注释的user_id将Exams链接到用户。

错误

a.lang.NullPointerException: null
    at java.util.HashMap.putMapEntries(HashMap.java:500) ~[na:1.8.0_65]
    at java.util.HashMap.putAll(HashMap.java:784) ~[na:1.8.0_65]
    at org.springframework.data.repository.query.ExtensionAwareEvaluationContextProvider$EvaluationContextExtensionAdapter.<init>(ExtensionAwareEvaluationContextProvider.java:470) ~[spring-data-commons-1.11.2.RELEASE.jar:na]
    at org.springframework.data.repository.query.ExtensionAwareEvaluationContextProvider.toAdapters(ExtensionAwareEvaluationContextProvider.java:210) ~[spring-data-commons-1.11.2.RELEASE.jar:na]
    at org.springframework.data.repository.query.ExtensionAwareEvaluationContextProvider.access$000(ExtensionAwareEvaluationContextProvider.java:59) ~[spring-data-commons-1.11.2.RELEASE.jar:na]
    at org.springframework.data.repository.query.ExtensionAwareEvaluationContextProvider$ExtensionAwarePropertyAccessor.<init>(ExtensionAwareEvaluationContextProvider.java:235) ~[spring-data-commons-1.11.2.RELEASE.jar:na]
    at org.springframework.data.repository.query.ExtensionAwareEvaluationContextProvider.getEvaluationContext(ExtensionAwareEvaluationContextProvider.java:107) ~[spring-data-commons-1.11.2.RELEASE.jar:na]
    at org.springframework.data.repository.query.ExtensionAwareEvaluationContextProvider.getEvaluationContext(ExtensionAwareEvaluationContextProvider.java:59) ~[spring-data-commons-1.11.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.SpelExpressionStringQueryParameterBinder.getEvaluationContext(SpelExpressionStringQueryParameterBinder.java:140) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.SpelExpressionStringQueryParameterBinder.evaluateExpression(SpelExpressionStringQueryParameterBinder.java:131) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.SpelExpressionStringQueryParameterBinder.potentiallyBindExpressionParameters(SpelExpressionStringQueryParameterBinder.java:89) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.SpelExpressionStringQueryParameterBinder.bind(SpelExpressionStringQueryParameterBinder.java:69) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.ParameterBinder.bindAndPrepare(ParameterBinder.java:172) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.ParameterBinder.bindAndPrepare(ParameterBinder.java:163) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.AbstractStringBasedJpaQuery.doCreateQuery(AbstractStringBasedJpaQuery.java:78) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.createQuery(AbstractJpaQuery.java:169) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.JpaQueryExecution$CollectionExecution.doExecute(JpaQueryExecution.java:114) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.JpaQueryExecution.execute(JpaQueryExecution.java:78) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:100) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:91) ~[spring-data-jpa-1.9.2.RELEASE.jar:na]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:462) ~[spring-data-commons-1.11.2.RELEASE.jar:na]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:440) ~[spring-data-commons-1.11.2.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:61) ~[spring-data-commons-1.11.2.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99) ~[spring-tx-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:281) ~[spring-tx-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96) ~[spring-tx-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:136) ~[spring-tx-4.2.4.RELEASE.jar:4.2.4.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.2.4.RELEASE.jar:4.2.4.RELEASE]

依赖

dependencies {
    compile 'org.springframework.boot:spring-boot-starter-thymeleaf'
    compile 'org.springframework.boot:spring-boot-starter-data-jpa'
    compile 'org.apache.tomcat:tomcat-dbcp:8.0.30'
    compile 'org.springframework.boot:spring-boot-starter-security'
    compile 'org.thymeleaf.extras:thymeleaf-extras-springsecurity4:2.1.2.RELEASE'}

@Entity
public class Exams {

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

    private String courseOffered;

    private String examType;

    private String subject;

    private String grade;

    private Long indexNumber;

    private Long gradeYear;

    private boolean isComplete;

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user;

    public Long getId() {
        return id;
    }

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

    public String getCourseOffered() {
        return courseOffered;
    }

    public void setCourseOffered(String courseOffered) {
        this.courseOffered = courseOffered;
    }

    public String getExamType() {
        return examType;
    }

    public void setExamType(String examType) {
        this.examType = examType;
    }

    public String getSubject() {
        return subject;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }

    public String getGrade() {
        return grade;
    }

    public void setGrade(String grade) {
        this.grade = grade;
    }

    public Long getIndexNumber() {
        return indexNumber;
    }

    public void setIndexNumber(Long indexNumber) {
        this.indexNumber = indexNumber;
    }

    public Long getGradeYear() {
        return gradeYear;
    }

    public void setGradeYear(Long gradeYear) {
        this.gradeYear = gradeYear;
    }

    public boolean isComplete() {
        return isComplete;
    }

    public void setComplete(boolean complete) {
        isComplete = complete;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }
}

ExamsDao

@Repository
public interface ExamsDao extends CrudRepository<Exams,Long>{
    @Query("select e from Exams e where e.user.id= ?#{principal.id}")
    List<Exams> findAll();
}

用户

@Entity
public class User implements UserDetails {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(unique = true)
    @Size(min = 8, max = 20)
    private String username;

    @Column(length = 100)
    private String password;

    @Column(nullable = false)
    private boolean enabled;

    @OneToOne
    @JoinColumn(name = "role_id")
    private Role role;

    @OneToOne(mappedBy = "user")
    private CertificateProgramme cert;

    private String programName;

    public Long getId() {
        return id;
    }

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

    public void setUsername(String username) {
        this.username = username;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public void setEnabled(boolean enabled) {
        this.enabled = enabled;
    }

    public Role getRole() {
        return role;
    }

    public void setRole(Role role) {
        this.role = role;
    }

    public CertificateProgramme getCert() {
        return cert;
    }

    public void setCert(CertificateProgramme cert) {
        this.cert = cert;
    }

    public String getProgramName() {
        return programName;
    }

    public void setProgramName(String programName) {
        this.programName = programName;
    }

    @Override
    public Collection<? extends GrantedAuthority> getAuthorities() {
        List<GrantedAuthority> authority = new ArrayList<>();
        authority.add(new SimpleGrantedAuthority(role.getName()));
        return authority;
    }

    @Override
    public String getPassword() {
        return password;
    }

    @Override
    public String getUsername() {
        return username;
    }

    @Override
    public boolean isAccountNonExpired() {
        return true ;
    }

    @Override
    public boolean isAccountNonLocked() {
        return true;
    }

    @Override
    public boolean isCredentialsNonExpired() {
        return true;
    }

    @Override
    public boolean isEnabled() {
        return enabled;
    }

}

角色

@Entity
public class Role {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Answer 1

尝试在查询中定义显式连接：

select e from Exams e join e.user u where u.id= ?#{principal.id}