JPA/Hibernate Static Metamodel Attributes not Populated -- NullPointerException_问答_开发者

I would like to use JPA2 Criteria API with metamodel objects, which seems to be pretty easy:

...
Root<JPAAlbum> albm = cq.from(JPAAlbum.class);
... albm.get(JPAAlbum_.theme) ... ;

but this Root.get always throws a NullPointerException. JPAAlbum_.theme was automatically generated by Hibernate and looks like

public static volatile SingularAttribute<JPAAlbum, JPATheme> theme;

but it's obviously never populated.

Am I missing a step in the initialization of the framework ?

EDIT: here is a snippet of how I use JPA and the metamodel when it's crashing:

    CriteriaBuilder cb = em.getCriteriaBuilder();

    CriteriaQuery<JPAAlbum> cq = cb.createQuery(JPAAlbum.class) ;
    Root<JPAAlbum> albm = cq.from(JPAAlbum.class);
    cq.where(cb.equal(albm.get(JPAAlbum_.theme).get(JPATheme_.id),
                        session.getTheme().getId())) ;

(JPAAlbum_ is a class, so I just import before) and the associated stacktrace:

Caused by: java.lang.NullPointerException
    at org.hibernate.ejb.criteria.path.AbstractPathImpl.get(AbstractPathImpl.java:138)
    at net.wazari.dao.jpa.WebAlbumsDAOBean.getRestrictionToAlbumsAllowed(WebAlbumsDAOBean.java:55)

EDIT 2:

In the JBoss EntityManager guide, I can see that

When the Hibernate EntityManagerFactory is being built, it will look for a canonical metamodel class for each of the managed typed is knows about and if it finds any it will inject the appropriate metamodel information into them, as outlined in [JPA 2 Specification, section 6.2.2, pg 200]

I could also verify with

     for (ManagedType o : em.getMetamodel().getManagedTypes()) {
            log.warn("___") ;
            for (Object p : o.getAttributes()) {
                log.warn(((Attribute)p).getName()) ;
            }
        }

that Hibernate is aware of my metamodel, the attribute names are written, however

   log.warn("_+_"+JPAPhoto_.id+"_+_") ;

remains desperately empty ...

EDIT3: here is the JPAAlbum entity and its metamodel class.

What else can I tell about my configuration ...

I use Hibernat 3.5.6-Final (according to META-INF/MANIFEST.MF),
deploy on Glassfish 3.0.1
from Netbeans 6.9.1;
and the application relies on EJB 3.1,

I hope it will help !

EDIT 4:

unfortunately, the JUnit test leads to the same exception:

java.lang.NullPointerException
    at org.hibernate.ejb.criteria.path.AbstractPathImpl.get(AbstractPathImpl.java:138)
    at net.wazari.dao.test.TestMetaModel.foo(TestMetaModel.java:55)

A much simpler project is available here/tarball. It only contains my entities and their metamodel, plus a JUnit test (foo crashes with metamodel, bar is okay with the usual Query.

EDIT 5:

You should be able to reproduce the problem by downloading the tarball, building the project:

ant compile
or
ant dist

and start the JUnit test net.wazari.dao.test.TestMetaModel

 CLASSPAT开发者_运维知识库H=`sh runTest.sh` java org.junit.runner.JUnitCore  net.wazari.dao.test.TestMetaModel

(edit runTest.sh to point CLASSPATH to the right location of your JUnit4-5 jar)

All the hibernate dependencies I use should be included in the archive.

I had the same issue and it was fixed by putting the Model and Model_ class into the same package.

I had a Java EE 6 application using EclipseLink on GlassFish with some @StaticMetamodel classes created and everything was working fine. When I switched to Hibernate 4 on JBoss 7, I started getting these NPEs too. I started investigating and I found this page:

http://docs.jboss.org/hibernate/entitymanager/3.6/reference/en/html/metamodel.html

It quotes the JPA 2 specification, section 6.2.1.1 which defines how the static metamodel classes should be built. For example, I found out by reading the spec that "the option of different packages will be provided in a future release of this specification". I had the metamodel classes in different packages and it worked fine on EclipseLink, but it's an extra feature, as the current standard indicates the following:

Metamodel classes should be in the same package as the entity classes they describe;
They should have the same name as the entity classes they describe, followed by an underscore (e.g. Product is the entity, Product_ is the metamodel class);
If an entity inherits from another entity or from a mapped superclass, its metamodel class should inherit from the metamodel class that describes its immediate superclass (e.g. if SpecialProduct extends Product, which extends PersistentObject, then SpecialProduct_ should extend Product_ which should extend PersistentObject_).

Once I followed all the rules in the spec (the above is just a summary, please refer to section 6.2.1.1 of the spec for the complete version), I stopped getting the exceptions.

By the way, you can download the specification here: http://jcp.org/en/jsr/detail?id=317 (click on "Download page" for the final release, choose to download the specification for evaluation, accept the agreement and download the file "SR-000317 2.0 Specification" - persistence-2_0-final-spec.pdf).

I can't reproduce the issue. I used some of your entities (simplified versions of JPAAlbum, JPATheme and JPATagTheme, without any interfaces), generated the metamodel classes and the following rudimentary test method (running inside a transaction) just passes:

@Test
public void foo() {
    CriteriaBuilder builder = em.getCriteriaBuilder();
    CriteriaQuery<JPAAlbum> query = builder.createQuery(JPAAlbum.class);

    Root<JPAAlbum> album = query.from(JPAAlbum.class);

    Assert.assertNotNull(album.get(JPAAlbum_.theme)); // no problem here

    query.where(builder.equal(album.get(JPAAlbum_.theme).get(JPATheme_.id), 1L));

    List<JPAAlbum> results = em.createQuery(query).getResultList();
}

FWIW, here is the generated SQL:

select
    jpaalbum0_.ID as ID32_,
    jpaalbum0_.AlbumDate as AlbumDate32_,
    jpaalbum0_.Description as Descript3_32_,
    jpaalbum0_.Nom as Nom32_,
    jpaalbum0_.Picture as Picture32_,
    jpaalbum0_.Theme as Theme32_ 
from
    Album jpaalbum0_ 
where
    jpaalbum0_.Theme=1

Tested with Hibernate EntityManager 3.5.6-Final, Hibernate JPAModelGen 1.1.0.Final, outside any container.

My suggestion would be to first try to reproduce (if reproducible) the problem in a JUnit test context.

PS: As a side note, I wouldn't store generated classes in the VCS.

Update: Here is a persistence.xml that you can use in a testing context:

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
  version="2.0">
  <persistence-unit name="MyPu" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>

    <class>com.stackoverflow.q3854687.JPAAlbum</class>
    <class>com.stackoverflow.q3854687.JPATheme</class>
    <class>com.stackoverflow.q3854687.JPATagTheme</class>

    <exclude-unlisted-classes>true</exclude-unlisted-classes>

    <properties>
      <!-- Common properties -->
      <property name="javax.persistence.jdbc.driver" value="${jdbc.driver}" />
      <property name="javax.persistence.jdbc.url" value="${jdbc.url}" />
      <property name="javax.persistence.jdbc.user" value="${jdbc.user}" />
      <property name="javax.persistence.jdbc.password" value="${jdbc.password}" />

      <!-- Hibernate specific properties -->
      <property name="hibernate.dialect" value="${jdbc.dialect}" />
      <!--
      <property name="hibernate.show_sql" value="true"/>
      -->
      <property name="hibernate.format_sql" value="true" />
      <property name="hibernate.hbm2ddl.auto" value="update" />   
    </properties>
  </persistence-unit>
</persistence>

I offer an alternative solution if putting the Model and Model_ in the same package does not work. You need to add one init() method to your class that builds the SessionFactory or EntityManager:

public class HibernateSessionFactory {
  private static SessionFactory factory;

  static {
    try {
        factory = new Configuration().configure().buildSessionFactory();
    } catch (Throwable ex) {
        throw new ExceptionInInitializerError(ex);
    }
  }

  public static SessionFactory getFactory() {
    return factory;
  }

  public static void init(){} //does nothing but elimating the NULLPOINTEREXCEPTION
}

So when you run your application from main method or a unit test you need to call HibernateSessionFactory.init(); first. Then the NullPointerException magically disappears and the application works.

This strange behaviour seems to happen when you pass a SingularAttribute around via method parameter.

Credit goes to @Can ÜNSAL who figured it all out in this question: Hibernate/JPA - NullPointerException when accessing SingularAttribute parameter

2019-04-24

The usual issue for unpopulated metamodel class attributes, is when the metamodel classes are in a different package than the corresponding managed classes.

The latest, JPA 2.2 specification still requires to have your metamodel classes in the same package as your corresponding managed classes.

Reference: Page 238, §6.2.1.1 Canonical Metamodel

FYI, I encountered a case where Hibernate creates a metamodel attribute but never initializes it, leading to a NullPointerException's when trying to use it.

public class Upper {
    public String getLabel() { return this.label; }
    public void setLabel(String label) { this.label = label; }
}

public class Lower extends Upper {
   @Override
   public String getLabel() { return super.getLabel(); }
}

Hibernate generate a label attribute declaration in both classes:

@Generated(value = "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
@StaticMetamodel(Upper.class)
public abstract class Upper_ {
    public static volatile SingularAttribute<Upper, String> label;
}

@Generated(value = "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
@StaticMetamodel(Lower.class)
public abstract class Lower_ {
    public static volatile SingularAttribute<Lower, String> label;
}

...and it will initialize Upper_.label but leave Lower_.label equal to null.

Boom.

The class and the metaModel should be in the same package, i.e.

Folder entities:

Eje
Eje_
Element
Element_

I attached one example of the metamodel code

import javax.annotation.Generated;
import javax.persistence.metamodel.SetAttribute;
import javax.persistence.metamodel.SingularAttribute;
import javax.persistence.metamodel.StaticMetamodel;
import java.util.Date;

@Generated(value = "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
@StaticMetamodel(Eje.class)
public abstract class Eje_ {
    public static volatile SingularAttribute<Eje, Integer> id;
    public static volatile SingularAttribute<Eje, String> name;
    public static volatile SingularAttribute<Eje, Integer> users;
    public static volatile SingularAttribute<Eje, Date> createdAt;
    public static volatile SingularAttribute<Eje, Date> updatedAt;
    public static volatile SetAttribute<Eje, FactorCritico> factorCriticos;
}

If nothing of above resolve this NPE issue, you also can check whether you are using List in your Entities relationships instead of Set.

I found out that using List's it is needed to declare ListAttribute instead of SetAttribute in the metamodel, otherwise, it provoke a NullPointerException and if you don't see the whole stack trace you will not notice that the metamodel was not initialized by your JPA specification.

Debbie's answer got me half of the way there.

There is another "name matching" voodoo gotcha.

Short version:

The "names" have to match between Model and the MetaModel for the "properties".

Longer version:

I was using non-easy-peezy names.

First the entities:

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import java.io.Serializable;
import java.time.OffsetDateTime;
import java.util.LinkedHashSet;
import java.util.Set;

@Entity
@Table(name = "DepartmentTable")
public class DepartmentJpaEntity implements Serializable {

    @Id
    @Column(name = "DepartmentKey", unique = true)
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long departmentKey;
    @Column(name = "DepartmentName", unique = true)
    private String departmentName;
    @Column(name = "CreateOffsetDateTime", columnDefinition = "TIMESTAMP WITH TIME ZONE")
    private OffsetDateTime createOffsetDateTime;
    @OneToMany(
            mappedBy = "parentDepartmentJpaEntity",
            cascade = CascadeType.PERSIST,
            orphanRemoval = true,
            fetch = FetchType.LAZY /* Lazy or Eager here */
    )

    private Set<EmployeeJpaEntity> employeeJpaEntities = new LinkedHashSet<>();

}

and

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
import java.io.Serializable;
import java.time.OffsetDateTime;

@Entity
@Table(name = "EmployeeTable")
public class EmployeeJpaEntity implements Serializable {

    @Id
    @Column(name = "EmployeeKey", unique = true)
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long employeeKey;

    @Column(name = "Ssn")
    private String ssn;

    @Column(name = "LastName")
    private String lastName;

    @Column(name = "FirstName")
    private String firstName;

    @Column(name = "CreateOffsetDateTime", columnDefinition = "TIMESTAMP WITH TIME ZONE")
    private OffsetDateTime createOffsetDateTime;

    //region Navigation
    
    @ManyToOne(fetch = FetchType.LAZY, targetEntity = DepartmentJpaEntity.class, cascade = CascadeType.PERSIST )
    @JoinColumn(name = "DepartmentForeignKey")
        private DepartmentJpaEntity parentDepartmentJpaEntity;
    //endregion

}

Note, my somewhat not default names. pay attention to the OnetoMany and ManyToOne object names.

Now, my meta-models:

import javax.persistence.metamodel.SetAttribute;
import javax.persistence.metamodel.SingularAttribute;

@javax.persistence.metamodel.StaticMetamodel(DepartmentJpaEntity.class)

public class DepartmentJpaEntity_ {
  public static volatile SingularAttribute<DepartmentJpaEntity, Long> departmentKey;
  public static volatile SetAttribute<DepartmentJpaEntity, EmployeeJpaEntity> employees; /* DOES NOT WORK :(  */
}

but this (below) will work, because I'm magic voodoo'ing the same names:

import javax.persistence.metamodel.SetAttribute;
import javax.persistence.metamodel.SingularAttribute;

@javax.persistence.metamodel.StaticMetamodel(DepartmentJpaEntity.class)

public class DepartmentJpaEntity_ {
  public static volatile SingularAttribute<DepartmentJpaEntity, Long> departmentKey;
  public static volatile SetAttribute<DepartmentJpaEntity, EmployeeJpaEntity> employeeJpaEntities;
}

and the other one:

import javax.persistence.metamodel.SingularAttribute;

@javax.persistence.metamodel.StaticMetamodel(EmployeeJpaEntity.class)

public class EmployeeJpaEntity_ {
  public static volatile SingularAttribute<EmployeeJpaEntity, Long> employeeKey;
  public static volatile SingularAttribute<EmployeeJpaEntity, DepartmentJpaEntity> parentDepartment;  /*does NOT work...its null at run time...no voodoo name matching */
}

But this does work:

import javax.persistence.metamodel.SingularAttribute;

@javax.persistence.metamodel.StaticMetamodel(EmployeeJpaEntity.class)

public class EmployeeJpaEntity_ {
  public static volatile SingularAttribute<EmployeeJpaEntity, Long> employeeKey;
  public static volatile SingularAttribute<EmployeeJpaEntity, DepartmentJpaEntity> parentDepartmentJpaEntity;
}

One of the reasons I purposely use non "standard" names for things is to flush out these voodoo setup issues at the beginning......in order to try and fail early...vs a failLater (hopefully in QA, not in production) issue(s) because someone renamed a property which seems benign at the time.