👀 Views: 2 💬 Answers: 1 📅 Created: 2025-06-05

java jackson deserialization spring-boot Java

I'm prototyping a solution and I recently switched to I'm following best practices but I'm sure I'm missing something obvious here, but I've looked through the documentation and I'm still confused about I'm working with a `ClassCastException` when trying to deserialize JSON into a custom class using Jackson....... I'm using Jackson 2.13.0 and Java 17 in my Spring Boot application. My custom deserializer is supposed to convert a JSON object into an instance of `MyCustomClass`, which has several fields, including a `List<String>` and a `Map<String, Integer>`. Here's the relevant part of my code: ```java import com.fasterxml.jackson.core.JsonParser; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.DeserializationContext; import com.fasterxml.jackson.databind.JsonDeserializer; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.annotation.JsonDeserialize; import java.io.IOException; import java.util.List; import java.util.Map; @JsonDeserialize(using = MyCustomDeserializer.class) public class MyCustomClass { private List<String> stringList; private Map<String, Integer> stringIntegerMap; // Getters and Setters } public class MyCustomDeserializer extends JsonDeserializer<MyCustomClass> { @Override public MyCustomClass deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException { // Custom deserialization logic // ... } } ``` When I send a request to my endpoint with JSON like this: ```json { "stringList": ["value1", "value2"], "stringIntegerMap": {"key1": 1, "key2": 2} } ``` I get the following behavior: ``` java.lang.ClassCastException: class java.util.HashMap want to be cast to class java.lang.String ``` I've checked my JSON input, and it matches the expected structure. I've also tried simplifying the deserialization logic in `MyCustomDeserializer`, but the exception still occurs. It seems to happen during the mapping of `stringIntegerMap`. I'm not sure what's causing this mismatch. Can anyone guide to troubleshoot this scenario or suggest best practices for implementing custom deserializers in Jackson? I'm working in a Linux environment. Cheers for any assistance! Any examples would be super helpful. How would you solve this?