ValueProxy and cyclic dependencies lead to infinite loop

[Ümit Seren]

I am not sure if this is a known issue. But I recently tried to map some JPA2 Entities to ValueProxy's and run into a weird issue.

In the database I have a table (Term) which references itself using an intermediate/mapping table (basically building a graph like structure).

Term ---> Term2Term.parent
Term <--- Term2Term.child

Basically a record from table A can have n childrin and exactly one parent (DAG).

The ValueProxy's look like this:

@ProxyForName(value="xxxxx")
public interface TermProxy extends ValueProxy {
    public Integer getId();
    ......
    public Set<Term2TermProxy> getParents();
    public Set<Term2TermProxy> getChilds();
}

@ProxyForName(value="xxxx")
public interface Term2TermProxy extends ValueProxy {

    public Integer getId();
    public TermProxy getParent();

    public TermProxy getChild();

}

Furthermore I have an EntityProxy in which one Term is embedded:

@ProxyForName(xxx)
public interface SomeEntityProxy extends EntityProxy{
    TermProxy getTraitOntologyTerm();

}

When I load the SomeEntityProxy object and also load the TermProxy I run into an infinite loop on the backend/server when serializing the payload with following exception:

java.lang.reflect.UndeclaredThrowableException
    at $Proxy118.hashCode(Unknown Source)
    at com.google.web.bindery.autobean.vm.impl.ShimHandler.hashCode(ShimHandler.java:66)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.google.web.bindery.autobean.vm.impl.ShimHandler.invoke(ShimHandler.java:76)
    at $Proxy118.hashCode(Unknown Source)
    at java.util.HashMap.hash(HashMap.java:351)
    at java.util.HashMap.put(HashMap.java:471)
    at java.util.HashSet.add(HashSet.java:217)
    at com.google.web.bindery.requestfactory.server.Resolver.resolveClientValue(Resolver.java:637)
    at com.google.web.bindery.requestfactory.server.Resolver.access$400(Resolver.java:51)
    at com.google.web.bindery.requestfactory.server.Resolver$PropertyResolver.visitReferenceProperty(Resolver.java:140)
    at com.google.web.bindery.autobean.shared.AutoBeanVisitor.visitCollectionProperty(AutoBeanVisitor.java:229)
    at com.google.web.bindery.autobean.vm.impl.ProxyAutoBean.traverseProperties(ProxyAutoBean.java:300)
    at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.traverse(AbstractAutoBean.java:166)
    at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.accept(AbstractAutoBean.java:101)
    at com.google.web.bindery.requestfactory.server.Resolver.resolveClientValue(Resolver.java:414)

I suspect that this is due to the fact that ValueProxy's don't have an identity and on the backend it traverse through all properties of my entity. However by having a reference from Term2Term back to Term I can end up with a cyclic dependency.

i.e. Term A -> Term2Term.parent -> Term B -> Term2Term.child -> Term A

If I break one of the relationships (parent or child) from Term to Term2Term it serializes fine. However when I adda nother ValueProxy (Term A -> SomeValueProxy -> Term A ) that contains a property which maps back to the Term, I again get a stackoverflow however this time on the client.

I guess switching to EntityProxy would solve the problem as the properties don't automatically get serialized and for identity the stableId is used.

[Thomas Broyer]

Is there a "Caused by" for this UndeclaredThrowableException?

[Ümit Seren]

So basically I get a stackoverflow with these two exceptions. I have to stop/kill the server to stop them.

I think the problem is in ValueProxyCategory. It calls the function hashCode() and this calls AutoBeanUtils.getAllProperties(bean).hashCode(); This retrieves all properties as a Map and then calculates the hashcode for each element. However because I have a cyclic dependency between Term and Term2Term it will go into an infinite loop.

Caused by: java.lang.reflect.InvocationTargetException

    at sun.reflect.GeneratedMethodAccessor88.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.google.web.bindery.autobean.vm.impl.BeanMethod$5.invoke(BeanMethod.java:155)
    at com.google.web.bindery.autobean.vm.impl.BeanMethod$1.invoke(BeanMethod.java:44)
    at com.google.web.bindery.autobean.vm.impl.SimpleBeanHandler.invoke(SimpleBeanHandler.java:43)
    at com.google.web.bindery.autobean.vm.impl.ShimHandler.hashCode(ShimHandler.java:66)
    at sun.reflect.GeneratedMethodAccessor77.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.google.web.bindery.autobean.vm.impl.ShimHandler.invoke(ShimHandler.java:76)
    at java.util.HashMap$Entry.hashCode(HashMap.java:818)
    at java.util.AbstractMap.hashCode(AbstractMap.java:494)
    at com.google.web.bindery.requestfactory.shared.impl.ValueProxyCategory.hashCode(ValueProxyCategory.java:55)

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