Скачать или смотреть How to Deserialize an Empty JSON Array into an Empty TreeMap in Java

Discover how to successfully manage empty JSON arrays in Java using Jackson by deserializing them into a properly initialized `TreeMap`.
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This video is based on the question https://stackoverflow.com/q/70235201/ asked by the user 'Scott Crooks' ( https://stackoverflow.com/u/928203/ ) and on the answer https://stackoverflow.com/a/70236124/ provided by the user 'pirho' ( https://stackoverflow.com/u/6413377/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding JSON Deserialization in Java with Jackson

When working with JSON data in Java, you might encounter cases where you need to deserialize an empty JSON array into a specific Java object. One common use case is deserializing an empty JSON array into a TreeMap<String, MyOtherClass>. This article is aimed at helping you resolve that issue when using Jackson, a popular library for processing JSON data.

The Problem

Imagine you have a class defined as follows:

[[See Video to Reveal this Text or Code Snippet]]

During the deserialization process, if you try to process JSON data containing an empty array for otherThings, you might run into an error like this:

[[See Video to Reveal this Text or Code Snippet]]

This error occurs because Jackson expects a TreeMap, but receives an empty array instead.

Proposed Solution

To handle this situation, you need to update your setOtherThings() method to effectively manage the conversion of an empty JSON array into a TreeMap. Here’s how to do it:

Step-by-Step Solution

Modify the Setter Method: Replace your existing setOtherThings() with a method that takes an array of MyOtherClass objects. It should properly check if the array is null and produce a TreeMap accordingly.

Here’s the updated version:

[[See Video to Reveal this Text or Code Snippet]]

Check for Empty Arrays: The updated setter uses Optional to handle potential nulls and guarantees that if it encounters an empty array, it will instantiate otherThings as a new TreeMap.

Collecting Elements: It utilizes Java Streams to effectively build the TreeMap based on the existing values within the input array, while maintaining the unique keys through Collectors.toMap().

Important Notes

If your JSON includes elements within otherThings, ensure to handle that case accordingly by adapting the stream logic.

Ensure that MyOtherClass has a proper method (getId()) to retrieve the identifier needed for your map.

Conclusion

By updating your setter method as outlined above, you can seamlessly deserialize empty JSON arrays into a TreeMap. This not only prevents the runtime errors you experienced but also sets a good foundation for handling more complex JSON structures in the future. With Jackson's powerful annotation-based data binding, you can easily manage JSON data according to your application's needs.

Implement this solution, and you'll be well on your way to efficiently working with JSON in Java!