Can an @Embeddable class be private?

Question

Is there is anything in the JPA specification that describes what a valid @Embeddable class can be? I have looked but cannot find anything.

I am using EclipseLink (2.3.0-M7 - full build string 2.3.0.v20110429-r9282) with Hibernate (3.6.4.Final) and Spring (3.0.5) and have set up my application as documented at EclipseLink/Examples/MOXy/Spring/JAXBAnnotations. Everything else currently works and has been for months. I was adding an @Embeddable class and started getting a NPE.

Here is some example code that I hope someone can use to reproduce this if it is a bug with EclipseLink because I remove EclipseLink library and configuration (and revert to Hibernate's implementation) then I no longer get the NPE.

Test class Broken.java

package x.y.z.model;

import javax.persistence.*;
import javax.xml.bind.annotation.*;
import java.io.Serializable;

@Entity
public class Broken {
    @EmbeddedId
    private Pk pk = new Pk();

    @Embeddable 
    private static class Pk implements Serializable {
        @ManyToOne
        private String foo;

        public String getFoo() {
            return this.foo;
        }
        public void setFoo(String foo) {
            this.foo = foo;
        }
    }
}

The Spring bean configuration I have is:

<bean id="jaxbMarshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
  <property name="contextPath" value="x.y.z.model"/>
</bean>
<bean id="xmlHelper" class="x.y.xml.XMLHelper">
  <property name="marshaller" ref="jaxbMarshaller"/>
</bean>

(see above link for XMLHelper class)

Finally I add the following to jaxb.index:

Broken

When starting the Spring application, I get the following exception:

ERROR org.springframework.test.context.TestContextManager 324 - Caught exception while allowing TestExecutionListener [org.springframework.test.context.support.DependencyInjectionTestExecutionListener@9b601d] to prepare test instance [x.y.z.service.AnyTest@198dc19]
java.lang.IllegalStateException: Failed to load ApplicationContext
    at org.springframework.test.context.TestContext.getApplicationContext(TestContext.java:308)
    at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:109)
    at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:75)
    at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:321)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:220)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:301)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:303)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:240)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:180)
    at org.apache.maven.surefire.junit4.JUnit4TestSet.execute(JUnit4TestSet.java:35)
    at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:115)
    at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:97)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.maven.surefire.booter.ProviderFactory$ClassLoaderProxy.invoke(ProviderFactory.java:103)
    at $Proxy0.invoke(Unknown Source)
    at org.apache.maven.surefire.booter.SurefireStarter.invokeProvider(SurefireStarter.java:150)
    at org.apache.maven.surefire.booter.SurefireStarter.runSuitesInProcess(SurefireStarter.java:91)
    at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:69)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jaxbMarshaller' defined in class path resource [applicationContext.xml]: Invocation of init method failed; nested exception is org.springframework.oxm.UncategorizedMappingException: Unknown JAXB exception; nested exception is
javax.xml.bind.JAXBException
 - with linked exception:
[java.lang.NullPointerException]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1420)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:519)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:291)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:288)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:190)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:580)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:895)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:425)
    at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:84)
    at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:1)
    at org.springframework.test.context.TestContext.loadApplicationContext(TestContext.java:280)
    at org.springframework.test.context.TestContext.getApplicationContext(TestContext.java:304)
    ... 31 more
Caused by: org.springframework.oxm.UncategorizedMappingException: Unknown JAXB exception; nested exception is javax.xml.bind.JAXBException
 - with linked exception:
[java.lang.NullPointerException]
    at org.springframework.oxm.jaxb.Jaxb2Marshaller.convertJaxbException(Jaxb2Marshaller.java:668)
    at org.springframework.oxm.jaxb.Jaxb2Marshaller.getJaxbContext(Jaxb2Marshaller.java:335)
    at org.springframework.oxm.jaxb.Jaxb2Marshaller.afterPropertiesSet(Jaxb2Marshaller.java:317)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1477)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1417)
    ... 44 more
Caused by: javax.xml.bind.JAXBException
 - with linked exception:
[java.lang.NullPointerException]
    at org.eclipse.persistence.jaxb.JAXBContext$ContextPathInput.createContextState(JAXBContext.java:661)
    at org.eclipse.persistence.jaxb.JAXBContext$ContextPathInput.createContextState(JAXBContext.java:621)
    at org.eclipse.persistence.jaxb.JAXBContext.<init>(JAXBContext.java:134)
    at org.eclipse.persistence.jaxb.JAXBContextFactory.createContext(JAXBContextFactory.java:108)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:128)
    at javax.xml.bind.ContextFinder.find(ContextFinder.java:249)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:372)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:337)
    at org.springframework.oxm.jaxb.Jaxb2Marshaller.createJaxbContextFromContextPath(Jaxb2Marshaller.java:355)
    at org.springframework.oxm.jaxb.Jaxb2Marshaller.getJaxbContext(Jaxb2Marshaller.java:328)
    ... 47 more
Caused by: java.lang.NullPointerException
    at org.eclipse.persistence.jaxb.javamodel.Helper.isBuiltInJavaType(Helper.java:261)
    at org.eclipse.persistence.jaxb.compiler.AnnotationsProcessor.shouldGenerateTypeInfo(AnnotationsProcessor.java:1526)
    at org.eclipse.persistence.jaxb.compiler.AnnotationsProcessor.processClass(AnnotationsProcessor.java:1029)
    at org.eclipse.persistence.jaxb.compiler.AnnotationsProcessor.processAdditionalClasses(AnnotationsProcessor.java:994)
    at org.eclipse.persistence.jaxb.compiler.AnnotationsProcessor.postBuildTypeInfo(AnnotationsProcessor.java:576)
    at org.eclipse.persistence.jaxb.compiler.AnnotationsProcessor.processClassesAndProperties(AnnotationsProcessor.java:230)
    at org.eclipse.persistence.jaxb.compiler.Generator.<init>(Generator.java:104)
    at org.eclipse.persistence.jaxb.JAXBContext$ContextPathInput.createContextState(JAXBContext.java:658)
    ... 60 more

If I change the @Embeddable class from private to public (and use EclipseLink), the NPE no longer occurs. So I have a solution that works but want to understand why.

Answer 1

The JPA 2.0 Specification states that embeddable classes must adhere to the same requirements stated for entities. Such requirements are stated in section 2.1 of the specification, and they state that:

• The entity class must have a no-arg constructor. It may have other constructors as well. The no-arg constructor must be public or protected.
• The entity class must a be top-level class. An enum or interface must not not be designated as an entity.
• The entity class must not be final. No methods or persistent instance variables of the entity class may be final.

Thus, I believe that what is affecting you could be that the embeddable class is not a top-level class, plus the fact that it is private.

You might like to give it try. Even if this is not the reason, you might like to consider following the recommendations of the standard, otherwise, you cannot guarantee your code is compliant with it.