I was having a terrible time with have mapped generic objects in Hibernate. MyObject defined a hierarchy, where you could retrieve either it’s children, or it’s parent. Something along the lines of:

@Entity
@Table(name = "MY_OBJECT")
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn(name = "MY_OBJECT_DISCRIMINATOR_COLUMN")
public abstract class MyObject<P extends MyObject<?, ?>, C extends MyObject<?, ?>> implements Serializable {
@Id
@Column(name = "ID")
private String id;

//Getters and Setters
}


Looks all fine and dandy from here, right? Executing anything involving this would give me a terrible stack trace, completely blowing up my Spring context, and ending in:

Caused by: org.hibernate.AnnotationException: Property MyObject.children has an unbound type and no explicit target entity. Resolve this Generic usage issue or set an explicit target attribute (eg @OneToMany(target=) or use an explicit @Type
at org.hibernate.cfg.PropertyContainer.assertTypesAreResolvable(PropertyContainer.java:136)
at org.hibernate.cfg.PropertyContainer.getProperties(PropertyContainer.java:114)
at org.hibernate.cfg.AnnotationBinder.addElementsOfClass(AnnotationBinder.java:1384)
at org.hibernate.cfg.InheritanceState.getElementsToProcess(InheritanceState.java:235)
at org.hibernate.cfg.AnnotationBinder.bindClass(AnnotationBinder.java:686)
at org.hibernate.cfg.Configuration$MetadataSourceQueue.processAnnotatedClassesQueue(Configuration.java:3977)
at org.hibernate.cfg.Configuration$MetadataSourceQueue.processMetadata(Configuration.java:3931)
at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1368)
at org.hibernate.cfg.Configuration.buildMappings(Configuration.java:1345)
at org.springframework.orm.hibernate3.LocalSessionFactoryBean.buildSessionFactory(LocalSessionFactoryBean.java:717)
at org.springframework.orm.hibernate3.AbstractSessionFactoryBean.afterPropertiesSet(AbstractSessionFactoryBean.java:211)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1477)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1417)
... 58 more


I thought, I don’t want to explicitly define a type, that’s why I’m using Generics! What slipped my mind was type erasure. By the time this code got executed, it had completely forgotten about the P and C for parent and children, and wouldn’t know that they types extend MyObject. In the end, I realized that it wasn’t asking for the concrete type for the target in OneToMany, and the abstract type would be fine. In the end, the fix was super simple, and I felt a little embarrassed. The modified code is as follows:

@ManyToOne(targetEntity=Content.class)
@JoinColumn(name = "PARENT_CONTENT_ID")
@JsonIgnore
private P parent;

@OneToMany(mappedBy = "parent", cascade = CascadeType.PERSIST, targetEntity=Content.class)
@JsonIgnore
private List<C> children;


I’ll get you next time Type Erasure!

The Maven Central Repo may or may not contain all the libraries you need when building. Common missing libraries may include:

• com.sun.jdmk:jmxtools:jar:1.2.1
• com.sun.jmx:jmxri:jar:1.2.1
• javax.jms:jms:jar:1.1

A quick way to fix this up is to add some more repositories to Maven.

You can add the repositories to either your project POM, your user settings.xml, or global settings.xml

<profile>
  <id>extra-repos</id>
  <repositories>
    <repository>
      <id>jboss-repository</id>
      <name>JBoss Deprecated Maven Repository</name>
      <url>https://repository.jboss.org/nexus/content/groups/public</url>
      <layout>default</layout>
      <releases><enabled>true</enabled><updatePolicy>never</updatePolicy></releases>
      <snapshots><enabled>false</enabled><updatePolicy>never</updatePolicy></snapshots>
    </repository>
    <repository>
      <id>maven2-repository.dev.java.net</id>
      <name>Java.net Repository for Maven</name>
      <url>http://download.java.net/maven/2/</url>
      <layout>default</layout>
    </repository>
    <repository>
      <id>maven2-repository.dev.java.net</id>
      <name>Java.net Repository for Maven</name>
      <url>https://repository.jboss.org/</url>
      <layout>default</layout>
    </repository>
  </repositories>
</profile>

After that, you can make sure this profile is always enabled by also adding it to your active profiles in your settings.xml

  <activeProfiles>
    <activeProfile>extra-repos</activeProfile>
  </activeProfiles>

Once you’ve added these additional repositories, you might also have to manually install some libraries. I ran into this problem with jmxtools.jar 1.2.1 and jmxri.jar 1.2.1. These have to be downloaded from Oracle; the jmx libraries I was looking for were found under jmx 1.2.1.

After downloading the libraries, you simply have to install them to your own repository. If you’re just using a local repository, it’s as simple as

mvn install:install-file -Dfile=jmxri.jar -DgroupId=com.sun.jmx -DartifactId=jmxri -Dversion=1.2.1 -Dpackaging=jar
mvn install:install-file -Dfile=jmxtools.jar -DgroupId=com.sun.jdmk -DartifactId=jmxtools -Dversion=1.2.1 -Dpackaging=jar