Jackson - @JsonTypeInfo property is being mapped as null?

Jackson - @JsonTypeInfo property is being mapped as null?

When using Jackson's @JsonTypeInfo annotation to include type information during serialization and deserialization, it's important to ensure that the property where the type information is stored is properly mapped. If the @JsonTypeInfo property is being mapped as null, there are several common reasons for this issue:

  1. Incorrect Property Name Mapping:

    • Make sure that the name of the property specified in @JsonTypeInfo matches the actual property name in your class.
    • Check for typos or differences in letter case (Jackson is case-sensitive by default).

    Example:

    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type") public class MyObject { // ... }

    Ensure that the property named "type" exists in your class and is correctly spelled.

  2. Getters and Setters:

    • Ensure that the property has both a getter and a setter method. Jackson uses these methods to access and set property values during serialization and deserialization.

    Example:

    public class MyObject { private String type; public String getType() { return type; } public void setType(String type) { this.type = type; } // ... }

  3. Visibility and Access Modifiers:

    • Ensure that the getter and setter methods for the property are correctly defined with appropriate access modifiers (e.g., public).
    • If they are not accessible, Jackson won't be able to read or write the property.

  4. No-Arg Constructor:

    • If your class defines a constructor with arguments, make sure to also provide a no-argument constructor (a constructor without any parameters). Jackson may use this constructor during deserialization.

    Example:

    public class MyObject { private String type; public MyObject() { // No-arg constructor } // ... }

  5. Custom Serialization/Deserialization:

    • If you've implemented custom serializers or deserializers for your class, ensure that they correctly handle the @JsonTypeInfo property.

  6. Configuration and Annotations:

    • Check if you have custom Jackson configuration that might affect how @JsonTypeInfo is processed.
    • Verify that there are no conflicting annotations or Jackson features that may interfere with type information handling.

  7. Missing Type Information:

    • Ensure that the type information specified in the @JsonTypeInfo annotation matches the actual type information in your data.

If you've checked all of these aspects and are still experiencing issues with the @JsonTypeInfo property mapping as null, you may want to provide more details about your specific code and class structure for further assistance.

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