Resolving the Kotlin Jackson Serialization Issue for PubSub Messages

Learn how to solve the `Kotlin Jackson` serialization issue with `PubSub` messages for smoother JSON handling and deserialization.
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This video is based on the question https://stackoverflow.com/q/70063015/ asked by the user 'Jonas Giedriauskas' ( https://stackoverflow.com/u/17472998/ ) and on the answer https://stackoverflow.com/a/70070679/ provided by the user 'dnault' ( https://stackoverflow.com/u/611819/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Kotlin Jackson Serialization Issue with PubSub

When working with Google Cloud PubSub, developers often encounter challenges related to message serialization and deserialization, especially when handling raw JSON. This guide dives into a specific problem faced during PubSub message handling in Kotlin, using Jackson for serialization. Let's explore how we can resolve this issue effectively.

The Problem at Hand

In your project, you're using a class named PubSubTemplate for sending messages to PubSub. The goal is to send a message containing raw JSON data. However, upon sending, you notice that the consuming application fails to deserialize the message correctly. The root of the issue lies in how the JacksonPubSubMessageConverter processes the payload. Specifically, it uses:

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

This results in double encoding, transforming the intended JSON into an incorrect format. For example, instead of sending the message as:

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

It gets sent as:

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

Now, let's walk through how to resolve this serialization issue effectively.

The Solution

To fix the serialization issue with your payload, you'll want to avoid the double encoding caused by the writeValueAsBytes method. Here's how you can create your payload correctly:

Steps to Correctly Handle Payload Serialization

Skip writeValueAsBytes: Since your payload is already in JSON string format, you can directly convert this string into bytes without any further encoding.

Use ByteString.copyFrom: Instead of using objectMapper.writeValueAsBytes(payload), simply convert your JSON string directly into a byte array.

Example Code Implementation

Below is a revised version of your original Kotlin code implementing these steps:

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

Explanation of the Code

Payload Initialization: The payload is assigned a valid JSON string directly.

ByteString Encoding: The ByteString.copyFrom(payload.toByteArray()) method is called directly on the JSON string, ensuring it’s converted into a byte array without double encoding.

Deserialization: The ObjectMapper reads the byte array back into the TestClass, allowing the application to consume the message without issues.

Conclusion

By understanding the nuances of JSON handling in Kotlin with Jackson and how PubSub messages are processed, you can effectively avoid pitfalls such as double encoding. Always remember to check whether your payload needs additional encoding steps or if it can be handled as-is.

Feel free to refer to this guide anytime you run into serialization issues with PubSub or any similar technology stack. Happy coding!