使用带有DozerMaper的parallelStream的对象列表映射给出了StackOverflowError

Question

I have the following utility-method to map a List of domain object to DTOs, resulting in a list of the mapped object.

   public static <Z, T> List<T> mapList(Mapper mapper, List<Z> source, Class<T> type) {
        List<T> result = new ArrayList<T>();
        int listSize = source.size();
        for (int i=0;i<listSize;i++) {
            result.add(mapper.map(source.get(i), type));
        }
        return result;
    }

As a mapper I pass a singleton-instance of DozerBeanMaper (instance managed by Spring). The List source is the result of a hibernate query. The above code work just fine.

Now, I've change to code to make use of the Stream API (I wanted to parallelize the mapping):

 public static <Z, T> List<T> mapList(Mapper mapper, List<Z> source, Class<T> type) {
     return source.parallelStream()
             .map((s) -> mapper.map(s, type))
             .collect(Collectors.toList());
}

And get the following :

Caused by: java.lang.NullPointerException
    at org.hibernate.engine.internal.StatefulPersistenceContext.getLoadedCollectionOwnerOrNull(StatefulPersistenceContext.java:755)
    at org.hibernate.event.spi.AbstractCollectionEvent.getLoadedOwnerOrNull(AbstractCollectionEvent.java:75)
    at org.hibernate.event.spi.InitializeCollectionEvent.<init>(InitializeCollectionEvent.java:36)
    at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:1895)
    at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:558)
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:260)
    at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:554)
    at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:142)
    at org.hibernate.collection.internal.PersistentSet.iterator(PersistentSet.java:180)
    at org.dozer.MappingProcessor.addOrUpdateToList(MappingProcessor.java:766)
    at org.dozer.MappingProcessor.addOrUpdateToList(MappingProcessor.java:850)
    at org.dozer.MappingProcessor.mapListToList(MappingProcessor.java:686)
    at org.dozer.MappingProcessor.mapCollection(MappingProcessor.java:553)
    at org.dozer.MappingProcessor.mapOrRecurseObject(MappingProcessor.java:434)
    at org.dozer.MappingProcessor.mapFromFieldMap(MappingProcessor.java:342)
    at org.dozer.MappingProcessor.mapField(MappingProcessor.java:288)
    at org.dozer.MappingProcessor.map(MappingProcessor.java:248)
    at org.dozer.MappingProcessor.map(MappingProcessor.java:197)
    at org.dozer.MappingProcessor.mapCustomObject(MappingProcessor.java:495)
    at org.dozer.MappingProcessor.mapOrRecurseObject(MappingProcessor.java:446)
    at org.dozer.MappingProcessor.mapFromFieldMap(MappingProcessor.java:342)
    at org.dozer.MappingProcessor.mapField(MappingProcessor.java:288)
    at org.dozer.MappingProcessor.map(MappingProcessor.java:248)
    at org.dozer.MappingProcessor.map(MappingProcessor.java:197)
    at org.dozer.MappingProcessor.map(MappingProcessor.java:187)
    at org.dozer.MappingProcessor.map(MappingProcessor.java:124)
    at org.dozer.MappingProcessor.map(MappingProcessor.java:119)
    at org.dozer.DozerBeanMapper.map(DozerBeanMapper.java:120)
    at 
org.mycompany.myproject.utils.BeanMapperUtil.lambda$0(BeanMapperUtil.java:30)

The execption repeats itself and finally turns into an StackOverFlowErorr.

If I use source.stream() instead of source.parallelStream() , I don't get any errors.

Any ideas?

Answer 1

The problem is that the method is called within a spring @Transactional annotated method together with lazy-loading. See eg this post] 1