Unable to deserialize lambda

by

You can’t deserialize an object without the class defining it. This hasn’t changed with lambda expressions.

Lambda expressions are a bit more complex as their generated runtime class is not the class which defined it but their defining class is the one holding the code of the lambda’s body and, in case of serializable lambdas, a deserialization support method which is called for validating and re- instantiating the lambda instance.

See SerializedLambda:

Implementors of serializable lambdas, such as compilers or language runtime libraries, are expected to ensure that instances deserialize properly. One means to do so is to ensure that the writeReplace method returns an instance of SerializedLambda, rather than allowing default serialization to proceed.

SerializedLambda has a readResolve method that looks for a (possibly private) static method called $deserializeLambda$(SerializedLambda) in the capturing class, invokes that with itself as the first argument, and returns the result. Lambda classes implementing $deserializeLambda$ are responsible for validating that the properties of the SerializedLambda are consistent with a lambda actually captured by that class.

So even if your instance was not referring to a synthetic method inside the defining class (e.g. in the case of a method reference to a method outside this class), deserialization still requires the $deserializeLambda$ for validating the correctness of the instance, intentionally.

Regarding the “good practice” of serializing lambdas, keep in mind that lambda expressions encapsulate behavior, not state. Storing behavior always implies storing just some kind of reference and requiring the code intended to restore it, to have implemented the associated behavior. That would work as well if you just referred to the intended behavior by a symbolic name or just stored, e.g. associated enum values.

More about the implications of having serializable lambdas is explained in this question.

More Related Contents:

  1. How to serialize a lambda?
  2. What is the difference between a lambda and a method reference at a runtime level?
  3. Possibility to explicit remove Serialization support for a lambda
  4. Difference between final and effectively final
  5. Java 8 Lambda function that throws exception?
  6. How can I throw CHECKED exceptions from inside Java 8 streams?
  7. Java 8 lambdas, Function.identity() or t->t
  8. Very confused by Java 8 Comparator type inference
  9. Break or return from Java 8 stream forEach?
  10. Lambda Expression and generic defined only in method
  11. Java 8: Difference between method reference Bound Receiver and UnBound Receiver
  12. Reflection type inference on Java 8 Lambdas
  13. java.lang.NullPointerException is thrown using a method-reference but not a lambda expression
  14. Why java.util.Optional is not Serializable, how to serialize the object with such fields
  15. Lambda expression to convert array/List of String to array/List of Integers
  16. Filter values only if not null using lambda in Java8
  17. Retrieving a List from a java.util.stream.Stream in Java 8
  18. Java “lambda expressions not supported at this language level”
  19. Java8: ambiguity with lambdas and overloaded methods
  20. Java 8, Streams to find the duplicate elements
  21. Java 8 Collectors.toMap SortedMap
  22. Java8 Lambdas and Exceptions
  23. Why can method reference use non-final variables?
  24. How to make a lambda expression define toString in Java 8?
  25. How can I throw CHECKED exceptions from inside Java 8 lambdas/streams?
  26. How to apply multiple predicates to a java.util.Stream?
  27. Parallel stream from a HashSet doesn’t run in parallel
  28. Non-interference exact meaning in Java 8 streams
  29. Cannot use Java 8 method with lambda arguments without specifying type arguments
  30. Creating String representation of lambda expression [duplicate]

Leave a Comment