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Learn how to post `Long` type data to a REST API with Spring Web Client by converting them to `String` format to avoid casting errors.
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How to Properly Post Long Type Data Using Spring Web Client

In the world of web development, integrating with REST APIs is a common practice. However, if you're using Spring Web Client to post data, you might encounter some unexpected challenges, especially when dealing with Long type the values.

One such issue arose when a developer attempted to send Long values using a MultiValueMap and faced a ClassCastException. In this guide, we'll delve into the problem and provide a comprehensive solution to ensure successful data posting to your REST API.

The Problem

The developer's code aimed to post form data containing Long values like this:

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

However, this code resulted in the following error:

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

The error message indicates that the MultiValueMap expects values to be of type String, but the provided values were of type Long. This led to casting problems that impeded the API call.

The Solution

To successfully post Long values using Spring Web Client, you need to convert your Long types to String manually. By ensuring all data in the MultiValueMap is in String format, you can avoid any casting issues.

Step-by-Step Implementation

Update the Type of MultiValueMap
Change the type parameter of MultiValueMap from Object to String. This ensures all values added are strings.

Convert Long to String
Use String.valueOf() to convert your Long values into strings before adding them to the MultiValueMap.

Here’s the corrected code:

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

Benefits of Manual Conversion

Control Over Data: By converting your Long values to String, you have complete control over the format of the data being sent, as opposed to relying on internal serialization or casting mechanisms.

Error Prevention: This approach reduces the risk of encountering unexpected type casting errors during runtime.

Conclusion

Properly posting Long type data using Spring Web Client can be straightforward if you take care to convert your values to String format. By following the steps outlined in this guide, you can avoid common pitfalls and ensure smooth communication with your REST APIs. Happy coding!