stream on JPA lazy list

by

Apparently, you are referring to this issue. These lazy lists using the anti-pattern of inheriting from actual implementations (here Vector) fail to adapt to the evolution of the base class. Note that there are two possible outcomes depending on how the anti-pattern was realized

  • If the lazily populated list populates itself (it terms of the inherited state) on the first use, the new inherited methods will start working as soon as a trigger property has been accessed for the first time
  • But if the list overrides all accessor methods to enforce delegation to another implementation, without ever updating the state of the base class, the base class’ methods which have not been overridden will never start working, even if the list has been populated (from the subclass’ point of view)

Apparently, the second case applies to you. Triggering the population of the list does not make the inherited forEach method work. Note that turning off the lazy population via configuration might be the simpler solution here.

To me, the cleanest solution would be if IndirectList inherits from AbstractList and adheres to the Collection API standard, now, almost twenty years after the Collection API has superseded Vector (should I mention how much younger JPA actually is?). Unfortunately, the developers didn’t go that road. Instead, the anti-pattern was maxed out by creating another class that inherits from the class which already inherits from the class not designed for inheritance. This class overrides the methods introduced in Java 8 and perhaps gets another subclass in one of the next Java releases.

So the good news is, developers expecting every List to be a Vector do not have to make up their minds, but the bad news is it doesn’t work as sometimes, you will not get the extended Java 8 specific version with JPA 2.6. But apparently, JPA 2.7 will work.

So you can derive a few alternative solutions:

  • Turn off lazy population
  • Stay with Java 7
  • Wait for JPA 2.7
  • just copy the collection, e.g.
    List<ElementParameter> workList=new ArrayList<>(elementParameters);
    This workList will support all Collection & Stream operations

More Related Contents:

  1. Why does this stream return no element?
  2. Java8 Collections.sort (sometimes) does not sort JPA returned lists
  3. How to convert to Java 8 map grouping by Map [closed]
  4. The JPA hashCode() / equals() dilemma
  5. Collection to stream to a new collection
  6. How to convert a Java 8 Stream to an Array?
  7. In Java, what are the advantages of streams over loops? [closed]
  8. How to sum a list of integers with java streams?
  9. Java 8 stream’s .min() and .max(): why does this compile?
  10. Why does Stream not implement Iterable?
  11. How can I create a stream from an array?
  12. In Java 8, is there a ByteStream class?
  13. Sum values from specific field of the objects in a list
  14. Files.walk(), calculate total size
  15. Does Stream.forEach respect the encounter order of sequential streams?
  16. Most efficient way to get the last element of a stream
  17. Why does findFirst() throw a NullPointerException if the first element it finds is null?
  18. Sort map by value using lambdas and streams
  19. Java 8 Stream IllegalStateException: Stream has already been operated on or closed
  20. Modifying Objects within stream in Java8 while iterating
  21. Take every nth element from a Java 8 stream
  22. Static context cannot access non-static in Collectors
  23. What Java 8 Stream.collect equivalents are available in the standard Kotlin library?
  24. How to check if exists any duplicate in Java 8 Streams?
  25. Java 8, how can I implement a switch statement using streams?
  26. Is it possible to write a generic enum converter for JPA?
  27. BigDecimal summary statistics
  28. What is a JPA implementation?
  29. Nested Java 8 parallel forEach loop perform poor. Is this behavior expected?
  30. Parallel flatMap always sequential

Leave a Comment