title: Upload image to S3 from webapp without storing it in server
body: <p>I have a web application with a Javascript Frontend and a Java Backend.
  I have a Use Case where the users can upload their profile pictures. The Use Case is simple: send the image from the user browser and store it in S3 with a maximum file size. Currently the Frontend sends the image data stream to the Backend, and this the stores the image in S3 using the AWS Java SDK.</p>
  
  <p>The Backend is obliged to previously store this image in a file system in order to know the image file size (and avoid reading more bytes than a certain maximum), since it is required by S3 to send the PUT Object Request along with the file Content Length.</p>
  
  <p>Is there any other way I can do this with AWS? Using another service? maybe Lambda? I don't like this method of having to previously store the file in a file system and then open again a stream to send it to S3.</p>
  
  <p>Thank you very much in advance.</p>