"Illegal attempt to map a non collection as a @OneToMany, @ManyToMany or @CollectionOfElements" in hibernate when annotating a ConcurrentHashMap

Question

I've tried annotating a property accessor whose return value is a map as follows:

@MapKeyColumn(name="parameter_name")
@ElementCollection
public ConcurrentHashMap<String, Serializable> getParameterValues()

This is in accordance with the hibernate user guide (section 2.2.5.3.4.). However, I get:

org.hibernate.AnnotationException: Illegal attempt to map a non collection as a @OneToMany, @ManyToMany or @CollectionOfElements: ConfigurationParameterBag.parameterValues
at org.hibernate.cfg.annotations.CollectionBinder.getCollectionBinder(CollectionBinder.java:324)
at org.hibernate.cfg.AnnotationBinder.processElementAnnotations(AnnotationBinder.java:1723)
at org.hibernate.cfg.AnnotationBinder.processIdPropertiesIfNotAlready(AnnotationBinder.java:796)
at org.hibernate.cfg.AnnotationBinder.bindClass(AnnotationBinder.java:707)
at org.hibernate.cfg.Configuration$MetadataSourceQueue.processAnnotatedClassesQueue(Configuration.java:4035)
at org.hibernate.cfg.Configuration$MetadataSourceQueue.processMetadata(Configuration.java:3989)
at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1398)
at org.hibernate.cfg.Configuration.generateDropSchemaScript(Configuration.java:1002)
at org.hibernate.tool.hbm2ddl.SchemaExport.<init>(SchemaExport.java:130)
at org.hibernate.tool.hbm2ddl.SchemaExport.<init>(SchemaExport.java:92)

Answer 1

Check out the topic 6.1. Persistent collections on this link .

From the link, Hibernate requires that persistent collection-valued fields be declared as an interface type. The actual interface might be java.util.Set, java.util.Collection, java.util.List, java.util.Map, java.util.SortedSet, java.util.SortedMap or anything you like ("anything you like" means you will have to write an implementation of org.hibernate.usertype.UserCollectionType.)