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Learn how to handle `null` responses in Spring Boot by returning a `JSON` response for not found items effectively.
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This video is based on the question https://stackoverflow.com/q/69408349/ asked by the user 'craftdeer' ( https://stackoverflow.com/u/7864525/ ) and on the answer https://stackoverflow.com/a/69408526/ provided by the user 'João Dias' ( https://stackoverflow.com/u/16572295/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Return a JSON Response for Not Found in Spring Boot?

When developing web applications using Spring Boot, you may encounter situations where a user requests an entity by its ID, but that ID does not exist in your database. It can be frustrating to only receive a null response without any information on what went wrong. To handle this scenario elegantly, it's essential to send back a meaningful JSON response indicating that the requested item was not found. In this guide, we will explore how to properly manage this situation within a Spring Boot application.

The Problem

Imagine you have an endpoint set up to return a Pet object based on its ID. However, if the ID does not exist in the database, the API should return a JSON object indicating that the pet was not found. The initial attempt to achieve this might lead to confusing responses. For example, you may find that your logger prints "pet found" even when an incorrect ID is provided. This indicates that the logic may not be implemented correctly.

Let's look at the initial code example that causes this problem:

Incorrect Approach

Here is how it was initially structured in PetController.java:

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

In the above code, there's a crucial mistake: the ResponseEntity is created without checking the existence of the pet. The matchingPet variable will always be non-null because it is initialized regardless of whether the ID exists.

The Solution

To correctly handle this scenario, we need to modify the code so that we check for the presence of the pet object before creating the ResponseEntity. Here's a structured solution:

Step 1: Modify the Controller

Update your getPetById method in the PetController as follows:

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

Step 2: Verify the Service Layer

Ensure that your PetServiceImpl is correctly accessing the repository. This is where you check for the presence of the pet using an Optional.

Here’s how it looks:

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

Step 3: Testing the Changes

After making these changes, conduct tests through your endpoint. Input different IDs:

For a valid ID, expect a 200 OK status with the pet's details in JSON format.

For an invalid ID, expect a 404 Not Found status.

Conclusion

By following the corrected structure above, your Spring Boot application will now effectively handle cases where a pet is not found by ID. Instead of receiving a null response, clients will receive a clear JSON message indicating that the requested resource was not available. This approach not only improves user experience but also adheres to good RESTful design principles.

In future developments, always ensure that your controllers return meaningful responses to users, especially in scenarios involving resource identifiers.

For more insights and Spring Boot tips, stay tuned for our upcoming posts!