Why am I getting a compile error when trying to deserialize JSON with Jackson into polymorphic types?

Deserialize JSON with Jackson into Polymorphic Types - Compile Error Clarification

The error encountered in the code snippet provided relates to the incorrect usage of the readValue method of ObjectMapper. Specifically, the argument types do not match the expected method signature.

Expected Method Signature:

public <T> T readValue(JsonParser jp, Class<T> valueType)
                          throws IOException, JsonProcessingException

Mistaken Method Call:

return mapper.readValue(root, animalClass);

In the mistaken call, the first argument is an ObjectNode instead of a JsonParser. This incorrect argument type arises because the code attempts to use mapper.readTree(jp) to retrieve an ObjectNode from the JsonParser. However, the correct method for this conversion is mapper.readtree(jp) (note the lowercased "t" in "Tree").

Solution:

To rectify the compile error, change the line to:

return mapper.readValue(mapper.readTree(jp), animalClass);

This correction ensures that the first argument to readValue is a JsonParser and the second argument is the target class type, animalClass.

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