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Question: I am trying to call a FastAPI endpoint from Mendix using a POST request with multipart/form-data, where the key "file" must contain an uploaded Excel file. I am facing multiple issues: The REST Call form-data configuration does not allow selecting a FileDocument in the "Value" field. The dropdown only shows simple types and does not provide a way to attach the uploaded file. When I create a Java Action in my module, the Binary return type is not available. Only String, Boolean, Integer, and Object are shown. Because of this, I cannot return byte[] or binary content. In Studio Pro, there is no "Java" tab under Preferences → Advanced. Also, when creating a Java Action, no .java file is generated inside the javasource folder. It seems like Java support is not active in my project, even though JDK 17 is installed on my system. Because Mendix cannot convert a FileDocument into binary, the REST POST request ends up sending an empty file. My FastAPI endpoint expects actual file bytes, so the backend receives no file and the process fails. I need help with the following: How can I enable full Java support in Mendix Studio Pro so that Binary return type becomes available, the Java tab appears, and Java source files are generated normally? How can I correctly convert a FileDocument into binary (byte[]) so that it can be sent through a REST Call as multipart/form-data? Is there a known issue with Java detection or configuration in Mendix 11.3, and what is the correct way to link JDK 17 so that Studio Pro recognizes it? Environment:Mendix Studio Pro version: 11.3JDK version: 17Windows OSUsing CommunityCommonsCalling external FastAPI REST endpoint

asked 2025-11-18

2 answers