Today I learned that in a Spring Boot REST API, you can nest custom data types to represent complex or hierarchical data structures. By creating Java classes to define these custom types, you can easily organize and encapsulate your data, making your API contracts more expressive and structured.

To use a custom type in the request payload, you simply include it as a parameter in your controller method with the @RequestBody annotation. Spring Boot will handle the deserialization of incoming JSON data into your custom type automatically.

Similarly, you can use a custom type as a return type in your controller method to send it back as part of the response payload. Spring Boot will handle the serialization of the custom type to JSON.

Additionally, you can create nested custom types by having one custom type contain other custom types or collections of custom types. This allows you to build sophisticated data hierarchies, representing more complex and meaningful data structures.

Overall, nesting custom types in a Spring Boot REST API is a powerful way to create more structured and organized APIs that efficiently handle intricate data representations.