fix: deserialize generic collection types with correct element types

[EvanYao826]

Fixes #16197

Problem

Hessian2 deserializes all small integers as Integer, causing ClassCastException when the expected type is Byte, Short, etc.

// Consumer sends
List<Byte> byteList = List.of((byte)1, (byte)2, (byte)127);

// Provider receives
List<Integer> byteList = List.of(1, 2, 127); // ClassCastException!

Root cause: Dubbo passes only the erased Class (e.g., List.class) to the serialization framework during request deserialization, discarding the generic Type (e.g., List<Byte>). Hessian2 has no way to know the expected element type.

Fix

In Hessian2ObjectInput.readObjectOfType(), after deserializing with the erased class, check if the declared type is a ParameterizedType. If so, convert collection/map elements to match the declared generic type arguments.

Changes

• Hessian2ObjectInput.java: Added convertGenericType() method that handles:

  • Collection types (List, Set) with element type conversion
  • Map types with key/value type conversion
  • Numeric type narrowing (Byte, Short, Float, Long, Double, Integer)
  • Both boxed and primitive number types

• ReflectionMethodDescriptor.java: Added getGenericParameterTypes() method to expose generic type information

• DecodeableRpcInvocation.java: Pass generic Type instead of erased Class to deserialization

• Hessian2SerializationTest.java: Added comprehensive tests for:

  • List<Byte>, List<Short>, List<Float>, List<Long>, List<Double>
  • Map<String, Byte>, Map<String, Short>
  • Mixed type collections

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 36.95%. Comparing base (3dbba26) to head (217ba35).

❗ There is a different number of reports uploaded between BASE (3dbba26) and HEAD (217ba35). Click for more details.

HEAD has 14 uploads less than BASE

Flag	BASE (3dbba26)	HEAD (217ba35)
samples-tests-java8	2	1
samples-tests-java21	2	1
integration-tests-java8	2	1
integration-tests-java21	2	1
unit-tests-java8	2	0
unit-tests-java25	2	0
unit-tests-java11	2	0
unit-tests-java17	2	0
unit-tests-java21	2	0

Additional details and impacted files

@@              Coverage Diff              @@
##                3.3   #16272       +/-   ##
=============================================
- Coverage     60.85%   36.95%   -23.91%     
+ Complexity    11779    11761       -18     
=============================================
  Files          1953     1952        -1     
  Lines         89186    89234       +48     
  Branches      13454    13395       -59     
=============================================
- Hits          54277    32974    -21303     
- Misses        29353    51663    +22310     
+ Partials       5556     4597      -959     

Flag	Coverage Δ
integration-tests-java21	32.11% <ø> (-0.06%)	⬇️
integration-tests-java8	32.24% <ø> (-0.01%)	⬇️
samples-tests-java21	32.11% <ø> (-0.12%)	⬇️
samples-tests-java8	29.79% <ø> (-0.11%)	⬇️
unit-tests-java11	?
unit-tests-java17	?
unit-tests-java21	?
unit-tests-java25	?
unit-tests-java8	?

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