What are the consequences of creating an ObjectMapper as a class field (not through Spring)?

Creating an instance of ObjectMapper as a class field without using Spring (i.e., without dependency injection) can lead to several issues:

• Potential thread-safety issues: although ObjectMapper is generally thread-safe for reading and writing, some of its configuration methods are not thread-safe. If you modify the ObjectMapper configuration after creation and use it across multiple threads, it may cause unpredictable behavior.

• Lack of centralized configuration: creating an ObjectMapper manually in each class or as a class field loses the ability to centrally manage serialization/deserialization settings, complicating maintenance and development.

• Increased code duplication: if different places create their own ObjectMapper instances, it leads to duplicated configurations and potential inconsistencies in behavior.

• Testing and extensibility issues: without DI, it is more difficult to replace ObjectMapper with a mock or custom instance in tests.

It is recommended to create and configure a single ObjectMapper instance and reuse it, or inject it via Spring to ensure centralized management and thread safety.