java.util.ConcurrentModificationException on CollectionOfElements

Question

Hi. I seem to get a ConcurrentModificationException when I have a CollectionOfElements inside an Embedabble.

If would like to have it like that, however If I change Route from Embedabble's to Entity than everything works fine. I have even tried adding @Version, but that doesn't seem to work.

Here are a snippet of my classes. Kart.java:

@Entity
public class Kart {

@Id @GeneratedValue
private Long id;

@Column(nullable=false,length=256)
@NotNull
@Length(max=256)
private String name;

@OneToOne(cascade=CascadeType.ALL)
private File file;

@Version
private int version;

@CollectionOfElements
private Set<Route> route;

Route.java:

@Embeddable
public class Route {

@Parent
private Kart kart;

@NotNull
@Column(nullable = false, length = 256)
private String name;

@NotNull
@Column(nullable = false)
private Boolean visible = Boolean.valueOf(true);

@CollectionOfElements
private Set<Coordinates> coordinates;

@Version
private int version;

Coordinates.java:

@Embeddable
public class Coordinates {

@NotNull
private int x;

@NotNull
private int y;

@Parent
private Route route;

@Version
private int version;

I have generated Hashcode/equals for Coordinates and Route

Answer 1

I can't give you any Hibernate-specific advice - but ConcurrentModificationExceptions often mean that a collection is being modified inside its iterator, such as

for (String s : myStringCollection)
{
    if (s.startsWith("XXX"))
    {
        myStringCollection.remove(s);
    }
}

Normally you can avoid this by explicitly creating an Iterator and calling its remove() method instead of the Collection's - but if this is internal Hibernate code you won't have that option.

Answer 2

The usage of "@CollectionOfElements" and "@Embeddable" is confusing. I assume you want Route and Coordinates to be separate tables? If so, they really shouldn't be @Embeddable. @Embeddable represents something that can be embedded into the parent table. As an example, to use composite keys you typically use an @EmbeddedId as your PK, which links to a class which is @Embeddable.

Since you mention that switching to Entity seems to fix the problem, I think you should switch Route and Coordinate to separate Entities. Then you will have a much more standard model setup which should clear your problem.

Answer 3

Check this JIRA entry.

ConcurrentModificationException when collection of embeddable contains a collection

It's a known bug in the Annotation Binder. And the issue lies in Hibernate Core which doesn't support collections in collections of embedded.