title: Append data to existing gridfs file
body: <p>As i can see java mongo driver does not provide capability to get <code>OutputStream</code> from existing gridFS file <code>com.mongodb.gridfs.GridFSFile</code></p>
  
  <p>I have to create <code>GridFSInputFile</code> directly or use <code>gridFs.createFile()</code> method. </p>
  
  <p>Is it a lack of java driver or a restriction of gridfs ? </p>
  
  <p>Could you suggest any workaround except create new file/delete old one ?</p>
  
  <p>Thank you</p>