Скачать или смотреть Solving the Jackson Deserialization Issue with Your POJO in Spring Boot

Discover how to effectively deserialize your POJO class sent from Angular to Spring Boot, avoiding common pitfalls with Jackson.
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This video is based on the question https://stackoverflow.com/q/63476186/ asked by the user 'Andrew Q' ( https://stackoverflow.com/u/11825629/ ) and on the answer https://stackoverflow.com/a/63477329/ provided by the user 'Mike' ( https://stackoverflow.com/u/4252674/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Can't Deserialize My POJO from Angular to Spring Boot? Here's the Fix!

If you've encountered the frustrating error message regarding deserialization of your POJO (Plain Old Java Object) in a Spring Boot application receiving an HTTP POST request from an Angular front end, you're not alone! This issue often arises when working with JSON data—specifically when the structure of your Java class does not allow Jackson (the JSON processor) to create instances of the class. In this guide, we'll walk through the reasons behind this issue and provide a clear solution for resolving it.

Understanding the Problem

When sending data from Angular to your Spring Boot backend, the data needs to be converted (or "deserialized") back into Java objects. In your case, you've defined a class named Menu, which is designed to represent items in your coffee shop application. However, Jackson throws a deserialization exception, indicating that it cannot create an instance of this class. The specific error message you might see is:

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

This indicates that Jackson is having trouble instantiating your Menu class from the incoming JSON structure. So, what's going wrong?

The Solution: Adding a Default Constructor

Why You Need a Default Constructor

The core of the issue is that Jackson relies on a default (no-argument) constructor to create an instance of your class before it populates the fields with data from the JSON object. If you only define a constructor with parameters (as you did in your Menu class), Jackson cannot create the object.

Here’s what you need to do to fix this:

Add a Default Constructor: Include a no-argument constructor in your Menu class. This allows Jackson to create an instance of your class without needing any parameters.

Implementing the Default Constructor

Here's how you can modify your Menu class:

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

Additional Considerations

Getters and Setters: Ensure that you have getters and setters for all the properties in your Menu class. Jackson uses these methods to set the values from the JSON.

JSON Structure: Ensure that the JSON structure being sent from Angular matches the expected structure in your Java class. In your case, it looks like the JSON is formatted correctly as follows:

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

Check the JSON Data Type: Make sure your Angular data types (e.g., Menu[] and property types in the interface) correspond accurately to the expected Java data types.

Conclusion

By adding a default constructor to your Menu class, you've resolved the deserialization problem that Jackson encountered when trying to map JSON data to your Java object. This key change will allow your Spring Boot application to successfully accept and process the orders sent from your Angular frontend. In software development, such small details can have a significant impact, so always remember to structure your POJOs with Jackson's requirements in mind.

Happy coding, and enjoy building your coffee shop application!