How to Use FileUpload with Quarkus RestClient for Multipart File Uploads

Описание: Learn how to send multipart file uploads using Quarkus RestClient by converting server-side FileUpload instances into client requests efficiently.
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This video is based on the question https://stackoverflow.com/q/79512397/ asked by the user 'Cristiano' ( https://stackoverflow.com/u/416104/ ) and on the answer https://stackoverflow.com/a/79514064/ provided by the user 'geoand' ( https://stackoverflow.com/u/2504224/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

In Quarkus, handling file uploads on the server side is straightforward using org.jboss.resteasy.reactive.multipart.FileUpload. However, sending files from a Quarkus RestClient to an external REST service requires a different approach, especially for multipart requests.

This post explains how to build multipart form requests in Quarkus RestClient by leveraging FileUpload instances received on the server, addressing common confusions about handling multipart data on the client side.



The Problem

You receive multipart file data in a server endpoint using FileUpload.

You need to send these files to an external REST API using a Quarkus RestClient.

The challenge: classes like DefaultFileUpload need non-public implementations and are not straightforward for client-side usage.



Solution Overview: Using ClientMultipartForm to Create Client Requests

Instead of trying to reuse server-side multipart classes directly, the recommended approach is:

Define your server request POJO to map multipart data.

Create a ClientMultipartForm for the client-side request.

Transfer file uploads and form attributes from the server request to the client form.

Example Server Request Class

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

Building the Client Multipart Form

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

Explanation

ClientMultipartForm.create() initializes a new multipart form for the client side.

attribute() adds simple text parts with their names.

fileUpload() adds file parts directly using the existing FileUpload instances from the server.



Additional Notes

ClientMultipartForm is the clean and official way to build multipart form requests on the client side in Quarkus REST Client.

Avoid trying to instantiate or manually implement low-level or server-specific multipart classes like DefaultFileUpload or FormValue.

This approach keeps your code clean and leverages Quarkus's multipart client support.



References

Quarkus REST Client Guide: Converting Received Multipart to Client Request



With this method, you can efficiently upload files from your Quarkus application to any external REST service accepting multipart requests.