How Can Jackson Be Used to Resolve Type Erasure During Deserialization of Generic Types?

Jackson and Generic Type Reference: Resolving Type Erasure in Deserialization

In your complex scenario, you're attempting to deserialize JSON data into a generic method that expects a MyRequest type. However, Jackson encounters an issue due to Java's type erasure, where the generic type T is not retained at runtime. Consequently, Jackson treats the nested MyRequest object as a Map, returning its contents as a LinkedHashMap when you call getMyObject() within the MyRequest instance.

To resolve this issue and specify the expected type to be returned as T, you need to provide Jackson with explicit type information. This can be achieved by constructing a JavaType object using the getTypeFactory() and constructCollectionType() methods:

<code class="java">JavaType type = mapper.getTypeFactory()
  .constructCollectionType(List.class, Foo.class);</code>

Replace List.class with the type of the list you expect to deserialize (e.g., List.class). Replace Foo.class with the expected type of the elements in the list (e.g., Customer.class).

Once you have the JavaType object, you can use it to deserialize the JSON data into the expected generic type:

<code class="java">List<Foo> list = mapper.readValue(new File("input.json"), type);</code>

By providing Jackson with this explicit type information, it will correctly deserialize the nested MyRequest object and return the actual T object when you call getMyObject().

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