Скачать или смотреть How to Effectively Set a Java Object from a JSON String in Spring Using Angular Data

Discover how to convert a JSON string obtained from Angular into a Java Object in Spring. Learn the correct approach with detailed steps and examples!
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This video is based on the question https://stackoverflow.com/q/62259643/ asked by the user 'Ajay Verma' ( https://stackoverflow.com/u/13573212/ ) and on the answer https://stackoverflow.com/a/62260190/ provided by the user 'Joost Papendorp' ( https://stackoverflow.com/u/13679554/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Effectively Set a Java Object from a JSON String in Spring Using Angular Data

In today's web applications, especially those developed with Angular and Spring Boot, developers often face the challenge of correctly parsing JSON strings received from client-side applications into Java objects on the server side. If you're working on a chat application using WebSocket, you might have stumbled upon an issue where deserialized Java objects appear with all null fields. In this guide, we will discuss how to resolve this problem step by step.

The Problem

When sending a message from Angular to your Spring Boot backend, you might find that the properties of the Java object (in this case, MessageModel) are not getting populated correctly, leading to every field showing as null. Here's a recap of the relevant Angular code sending the MessageModel:

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

Upon receiving this message on the backend, the Java code might look something like this:

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

When you print the message, you may see something like this:

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

Yet the output for msg shows all null values:

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

The Solution

The issue arises because the Gson library expects a matching structure between the JSON string and the Java object. In your current setup, the MessageModel class does not directly correspond to the structure of the incoming JSON. To resolve this, you need to introduce a wrapper class that accurately reflects the JSON format.

Step 1: Create a Wrapper Class

You need to create a new class, MessageWrapper, which will contain a MessageModel object to match the structure of the JSON string being sent from Angular. Here's how it might look:

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

Step 2: Modify the Existing Java Method

Next, you should update your processMessageFromClient method to deserialize the JSON string into the MessageWrapper class. This way, Gson can correctly populate the MessageModel fields nested within the wrapper. Here’s how the updated method appears:

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

Step 3: Understand the Final Structure

The received JSON now translates to:

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

This structure perfectly matches the MessageWrapper class, allowing Gson to recursively decode the inner MessageModel properties.

Final Thoughts

By implementing these changes, you ensure that the MessageModel object gets correctly populated with the values sent from Angular, eliminating the issue of nulls in your deserialized Java objects. This method not only clarifies the deserialization process but also enhances the structure and maintainability of your code.

Now you should be equipped to properly convert JSON strings from Angular into Java objects in Spring systems! Experiment with your chat application and see these changes take effect.