Programmatically loading Entity classes with JPA 2.0?

Solution 1:

With the help of Spring I did this in a JPA compliant way.

My "persistence.xml" looks empty, with no entities listed within the <persistence-unit> element.

I then wrote a class that implemented PersistenceUnitPostProcessor like so:

import java.util.Set;
import javax.persistence.Entity;
import javax.persistence.MappedSuperclass;
import org.reflections.Reflections;
import org.reflections.scanners.TypeAnnotationsScanner;
import org.springframework.orm.jpa.persistenceunit.MutablePersistenceUnitInfo;
import org.springframework.orm.jpa.persistenceunit.PersistenceUnitPostProcessor;

public class ReflectionsPersistenceUnitPostProcessor implements PersistenceUnitPostProcessor {

    private String reflectionsRoot;
    private Logger log = LoggerFactory.getLogger(ReflectionsPersistenceUnitPostProcessor.class);

    @Override
    public void postProcessPersistenceUnitInfo(MutablePersistenceUnitInfo pui) {
            Reflections r = new Reflections(this.reflectionsRoot, new TypeAnnotationsScanner());
            Set<String> entityClasses = r.getStore().getTypesAnnotatedWith(Entity.class.getName());
            Set<String> mappedSuperClasses = r.getStore().getTypesAnnotatedWith(MappedSuperclass.class.getName());

            for (String clzz : mappedSuperClasses)
            {
                    pui.addManagedClassName(clzz);
            }


            for (String clzz : entityClasses)
            {
                    pui.addManagedClassName(clzz);
            }

    }

    public String getReflectionsRoot() {
            return reflectionsRoot;
    }

    public void setReflectionsRoot(String reflectionsRoot) {
            this.reflectionsRoot = reflectionsRoot;
    }
}

Then I adjusted my spring context xml like this:

<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
            <property name="dataSource" ref="dataSource" />
            <property name="jpaVendorAdapter">
                    <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                            <property name="showSql" value="false" />
                            <property name="generateDdl" value="true" />
                            <property name="databasePlatform" value="org.hibernate.dialect.MySQL5InnoDBDialect" />
                    </bean>
            </property>
            <property name="persistenceUnitName" value="GenericPersistenceUnit"/>
            <property name="persistenceXmlLocation" value="classpath:META-INF/persistence.xml"/>
            <property name="persistenceUnitPostProcessors">
                    <list>
                            <bean class="com.austinmichael.core.repository.ReflectionsPersistenceUnitPostProcessor">
                                    <property name="reflectionsRoot" value="com.austinmichael"/>
                            </bean>
                    </list>
            </property>
    </bean>

Note the registration of the ReflectionsPersistenceUnitPostProcessor in the persistenceUnitPostProcessors setting.

And that's it. Every class with a JPA Entity or MappedSuperclass annotation on the classpath is added to the classpath. I had to give reflections the prefix of a package name to scan through which is why com.austinmichael is there at all. You could register a second ReflectionsPersistenceUnitPostProcessor with a different package name prefix if you want if your entities don't share a common package name prefix.

But, this is now JPAVendor agnostic.

Solution 2:

Is there a way to do the same thing - programmatically loading your Entity classes - in a JPA 2.0 compliant way?

No, this is not supported by JPA so you'll have to do this in a provider specific way. James Sutherland described the process for EclipseLink in this thread like this:

You can access the EclipseLink ServerSession from the EntityManagerFactoryImpl (getServerSession()), and use its' addDescriptor(ClassDescriptor) or addDescriptors() API to add EclipseLink ClassDescriptor. You will need to build the ClassDescriptor meta-data objects directly yourself (or use the Mapping Workbench to create them), as loading from JPA annotations or orm.xml would be more difficult.

Also have a look at this more recent thread for more code sample (the API looks like a bit verbose).

References

• Re: [eclipselink-users] Close to get it. Just a little help
• Re: JPA: adding entities to EntityManagerFactory programmatically