Скачать или смотреть Solving the Spring Controller Not Returning Valid JSON Issue in Your Angular Application

Discover how to resolve JSON parsing errors between your Spring boot backend and Angular frontend by correctly returning JSON data.
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Solving the Spring Controller Not Returning Valid JSON Issue in Your Angular Application

Connecting a backend server written in Java with a frontend framework like Angular is a common task in modern web development. However, it can also lead to issues, especially when it comes to data handling and serialization. One recurring problem many developers encounter is the backend not returning valid JSON data, leading to significant headaches when trying to parse it on the frontend. In this guide, we will address a specific scenario involving a Spring Boot controller that reports a JSON parsing error and guide you through a step-by-step solution.

The Problem

As detailed in a user's query, an error appears in the console stating:

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

This error suggests that the response from the backend is not in a proper JSON format, which is necessary for the Angular HttpClient to process it correctly. The root issue lies within the getServices method of your Spring Boot controller. Let's take a look at the code before we move to the solution.

Existing Code Snippet

Here’s the core section of the existing controller that is causing the issue:

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

The method is designed to retrieve a list of Services from a Firestore database and return it as a JSON string. However, instead of converting the List<Services> directly to JSON, it is being converted to a plain string, which is why the frontend fails to parse it properly.

The Solution

To resolve this issue, you'll need to make some changes to your controller to ensure it returns a correctly formatted JSON response.

1. Use ObjectMapper for JSON Serialization

Instead of using toString(), you should utilize Jackson's ObjectMapper to convert your list of services into a JSON string. Here's how you can do this step-by-step:

Add the ObjectMapper dependency (if not already included):
Make sure you have the jackson-databind library available. If you're using spring-boot-starter-web, this should already be included as a dependency.

Autowire the ObjectMapper:
Incorporate the ObjectMapper in your ProvidersController as follows:

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

Modify the getServices Method:
Update your getServices method to return the JSON response by using the writeValueAsString method of the ObjectMapper:

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

2. Verify Frontend Data Handling

After making the changes in your Spring Boot app, verify that your Angular service is set up correctly to handle the JSON response. Your HomeItemService code appears to be formed correctly, making a GET request to the right endpoint. If you encounter additional errors, ensure that the Angular models align with the structure of the JSON data returned from your backend.

Conclusion

In this guide, we have tackled the issue of a Spring Boot controller not returning valid JSON data. By correctly using the ObjectMapper to serialize your data instead of relying on a string representation, you can ensure that your Angular frontend can parse the data as expected. These steps will streamline the integration between your frontend and backend, allowing for a smoother development experience. If you continue to experience issues, don't hesitate to reach out for assistance or consult the documentation for additional guidance.

Feel free to implement these changes and enhance your application. Happy coding!