Why Does Postman Keep Changing My Content-Type to application/json When I Just Want to Upload an Excel File? (I Might Just Become a Flower Gardner)

Hey fellow developers and fellow victims of Postman and Insomnia (those "helpers" that promise to make our lives easier), let me tell you the most absurd thing that’s been happening in my API testing journey. I’ve been working on a Spring Boot application to upload and process an Excel file, and, naturally, I needed to use the mighty @RequestParam MultipartFile file to handle that data. Simple, right? Wrong.

I don’t know if Postman and Insomnia are in a secret rivalry to frustrate developers, but it's like they’ve been conspiring to throw me into a world of confusion. I just want to upload a basic Excel file. I don't need fancy JSON, and I don’t need my Content-Type to be application/json. I need multipart/form-data, because, well, it’s a file, and that’s what I’m uploading. But apparently, Postman hasn’t gotten the memo. And Insomnia… don’t even get me started. It's like they’re both on an endless loop of mischief.

A Simple Task: Upload an Excel File to My Spring Boot API

All I need is a simple file upload. Simple.

Here’s what I thought would happen:

1. I open Postman or Insomnia.
2. I choose multipart/form-data.
3. I add the key file (because that’s what the Spring Boot controller expects).
4. I pick my Excel file (because that’s what I want to upload).
5. Postman or Insomnia automatically decides that the only reasonable thing to do is to add the correct Content-Type, which, in this case, should be multipart/form-data.

But NO. Here’s what actually happens:

• Postman goes ahead and sets the Content-Type to application/json. For a file upload. A FILE upload. What is that even supposed to mean?
• I check the body, and Postman has somehow convinced itself that I’m uploading JSON instead of an Excel file. Postman, please. It’s a file, not JSON. Just, no.
• I try to manually change the Content-Type to multipart/form-data. Postman doesn't even care. It just reverts back to application/json like it knows better than I do.

At this point, I begin to question my career choices.

But Wait, It Gets Better

Then there’s Insomnia, Postman’s competitor. I think, "Maybe Insomnia will be more sensible." I mean, it's not as overconfident as Postman, right?

But no. Insomnia also has this uncanny ability to make decisions for me. It refuses to keep the correct Content-Type. Instead, Insomnia goes ahead and auto-selects application/json. It’s like Insomnia is saying, “You know what? You don’t actually want to upload a file. You just want to send some JSON data. Trust me on this one."

No Insomnia. I don’t need your JSON. I need Excel.

The Only Logical Conclusion: Flower Gardening

After hours of debugging, trying to adjust headers, and setting form-data correctly, I’ve come to a conclusion: I’m done with this. I’ve had enough. I’m going to leave the world of APIs and Postman headaches behind. I’ll switch careers and start fresh in a new, less frustrating field—flower gardening.

In the world of flowers, you don't get the cruel and unexpected behavior of apps like Postman. Flowers don’t change the content-type of your requests to application/json when you just want to plant a tulip. There’s no confusing headers or mismatched body types. You just plant seeds, and they grow. It's a beautiful, logical process. No more surprises.

Tomorrow, We Try Again

But hey, maybe tomorrow, we’ll try again. Maybe tomorrow Postman and Insomnia will wake up and decide, “Okay, maybe we’ll let the user upload their file without forcing them into a JSON nightmare.” Maybe tomorrow I’ll finally be able to upload my Excel file with the correct multipart/form-data and live my life without Postman reverting my hard work into some JSON mess.

Until then, I’ll be in the garden, planting some sunflowers and wondering if APIs are worth the stress. ??