Скачать или смотреть How to Fix No Serializer Found Error in Your Spring Boot Project

Learn how to handle the `No serializer found for class java.io.FileDescriptor` error in your Spring Boot application by disabling `SerializationFeature.FAIL_ON_EMPTY_BEANS`.
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This video is based on the question https://stackoverflow.com/q/66639713/ asked by the user 'Kevin' ( https://stackoverflow.com/u/10494588/ ) and on the answer https://stackoverflow.com/a/66642322/ provided by the user 'crizzis' ( https://stackoverflow.com/u/1092818/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting the No Serializer Found Error in Spring Boot

When developing applications with Spring Boot, encountering serialization errors can be quite common. One such error that developers often face is:

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This error usually arises when the framework is unable to serialize an object to JSON, which can occur in scenarios where a method is attempting to return a MultipartFile in a response entity. In this guide, we will walk through the potential causes of this issue and how to resolve it effectively.

Understanding the Problem

The root cause of the error lies in the Spring MVC controller where the uploadImage method attempts to return a MultipartFile as part of the response. Spring tries to convert the MultipartFile to JSON format, but it doesn't know how to handle it, leading to serialization problems.

Here's a brief breakdown:

Error Context: The error arises when calling ResponseEntity.ok(imageFile) in the uploadImage method of a controller.

Reason for Error: Spring does not support JSON serialization for MultipartFile as it is not a simple POJO (Plain Old Java Object).

Implementing the Solution

To resolve this issue, the solution is to ensure that the controller returns a response that Spring can handle properly. Instead of returning the MultipartFile itself, the focus should be on returning a response that contains relevant information—like the download URL of the uploaded file.

Step-by-Step Solution

Modify the uploadImage Method:
Adjust the method to return the result of uploadToLocalFileSystem, which provides a ResponseEntity<String>. Here's how to do it:

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Update uploadToLocalFileSystem in Service:
Ensure that the uploadToLocalFileSystem method in your ProductService class calls the appropriate method from ProductServiceUtils that handles the file upload.

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Handling MultipartFile State:
As a best practice, refrain from storing state (like imageFile or fileDownloadUri) in singleton beans, as this can lead to thread-safety issues. Try to make your service stateless by ensuring every method returns all necessary information in its response.

Conclusion

By returning the result of the ProductServiceUtils.uploadToLocalFileSystem() method from your controller, you avoid serialization issues with MultipartFile. This solution will not only eliminate the error but will also make your API more robust and thread-safe.

In summary, handling multipart file uploads in Spring Boot requires careful management of responses and understanding of serialization. Keep learning and experimenting, and you'll become proficient in managing these types of problems in your Java applications.

Remember to test your API after making these changes, ensuring that file uploads now return the expected results without any errors. Happy coding!