👀 Views: 2 💬 Answers: 1 📅 Created: 2025-06-06

jackson json classcastexception Java

I recently switched to Hey everyone, I'm running into an issue that's driving me crazy. This might be a silly question, but I've been struggling with this for a few days now and could really use some help. I'm working with a `ClassCastException` when trying to deserialize a JSON response into a Java object using Jackson. The JSON structure is a bit complex, and I'm not sure how to properly map it to my Java classes. Here's an example of the JSON I'm dealing with: ```json { "data": { "items": [ { "id": 1, "name": "Item 1" }, { "id": 2, "name": "Item 2" } ], "metadata": { "total": 2, "page": 1 } } } ``` I have created the following classes for deserialization: ```java public class Response { private Data data; // getters and setters } public class Data { private List<Item> items; private Metadata metadata; // getters and setters } public class Item { private int id; private String name; // getters and setters } public class Metadata { private int total; private int page; // getters and setters } ``` When I attempt to deserialize this JSON using the following code: ```java ObjectMapper objectMapper = new ObjectMapper(); Response response = objectMapper.readValue(jsonString, Response.class); ``` I receive the behavior: ``` Exception in thread "main" java.lang.ClassCastException: class java.util.HashMap want to be cast to class java.util.List ``` I've double-checked that the JSON structure matches my Java classes. I also tried using `@JsonProperty` annotations to ensure the field names are correctly mapped, but it still throws the same exception. I suspect it might be due to the way Jackson is handling the JSON arrays. Is there anything in my setup that could lead to this scenario, or do I need to adjust my class definitions further? Any insights on how to resolve this would be greatly appreciated! What's the best practice here? Thanks in advance! I'm coming from a different tech stack and learning Java. What's the best practice here? My team is using Java for this application. I'm open to any suggestions.