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Learn how to deserialize JSON objects based on multiple properties using Jackson, and eliminate redundancy in your data structure.
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Simplifying JSON Deserialization with Jackson: Inferring TYPE from Multiple Properties

When working with REST APIs, efficiently handling JSON data is crucial, especially when your application relies on specific object types. In this guide, we’ll explore a common challenge developers face: how to deserialize JSON objects using Jackson based on more than one property. Specifically, we’ll focus on situations where the TYPE can be inferred either from the ID field or explicitly provided in the JSON.

The Problem

Imagine a scenario where you are creating or updating objects in your application. The following two cases illustrate the challenge:

Object Creation: The object does not have an ID yet, but it does contain a TYPE property.

Example JSON:

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Object Update: The object has an ID, and although the TYPE can be inferred from the ID, it’s not explicitly included in the JSON.

Example JSON:

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The challenge arises when we want to deserialize both objects into a Dog object without redundancy. In the second case, while you can add the TYPE property manually, it feels unnecessary since we can derive it from the ID.

The Solution

To address this problem, we can implement a workaround that allows for injecting the required data when needed, specifically the TYPE, before parsing the root node with Jackson’s ObjectMapper. Here’s a step-by-step guide on how to achieve this.

Step 1: Read the JSON Input

First, we need to read the incoming JSON string into a JsonNode structure using Jackson's ObjectMapper.

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Step 2: Iterate Through the JSON Fields

Once we have the JSON root node, we can iterate through the fields to check if each object contains the required TYPE property. If it’s missing and an ID is present, we’ll infer the TYPE from the ID.

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Step 3: Inject Data When Necessary

The injectData method will perform the injection of the TYPE into the JSON if it’s missing. Here’s the code for the injectData method:

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Step 4: Inference Logic

Don't forget to define how to infer the TYPE from the ID. This part of the code should be adapted based on your specific application logic, which determines the appropriate type string.

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Conclusion

Using this approach, you can effectively deserialize JSON objects without redundancy in the second case. By inferring the TYPE from the ID, you streamline the JSON structure your API consumes and responds with, leading to cleaner, easier-to-manage data.

If you need further assistance or clarification, feel free to reach out in the comments or check out the Jackson documentation!