Sensei API Integration with my Java servlets

I need to automate y workflow by using sensei API for cutout and mask generation. I can upload and download the file using Java servlet doGet and doPut method

In the curl i have specified the following

"input":{
"storage":"external",
"href":"https://<>com/download?fileName=/work/passport/adcd/test.jpg"
},
"output":{
"storage":"external",
"href":"https://<>com/upload?qquuid=adcd",
"mask":{
"format":"soft"
}

The doPut method is invoked. But i am not sure how to write the content to file system

Is there any example of API integration with Java system end point