Introduction to the differences between form POST submission of common fields and submission of attachments for transmission

I was suddenly asked this question today, and I didn’t even know how to explain it clearly. So I wrote a servlet in java to test it, as shown in the figure below.
Form post method to submit common fields:

Form post submission attachment:

Attached:
Form GET Submit common fields:

Form GET submission attachment:

##For more information on the differences between form POST submission of ordinary fields and submission of attachments for transmission, please pay attention to the PHP Chinese website!