Need to use file as a parameter in groovy scripts

Summary: Need to use a file as a parameter in groovy script and send it in the form of multipart-form-data to the WebService.

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I have to send a file along with other parameters from js to Groovy Object function. then for the corresponding WebService I have to send the payload as multipart-form-data which includes this file. So how can i pass the file from js to groovy as a parameter. And how to send the payload as multipart-form-data to the WebService.

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