Programmatically loading Entity classes with JPA 2.0?

Question

With Hibernate you can load your Entity classes as:

sessionFactory = new AnnotationConfiguration()                     .addPackage("test.animals")                     .addAnnotatedClass(Flight.class)                     .addAnnotatedClass(Sky.class)                     .addAnnotatedClass(Person.class)                     .addAnnotatedClass(Dog.class); 

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

The reason for this question is because I'd like to dynamically load my Entity classes, thus not necessarily programmatically.

Answer 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.