Android open file input stream from uri

I'm trying to upload a file by copying it from mobile app to server app running on windows. I used a file chooser to let the user select the file:

public void openFile(View view) {
        Intent intent = new Intent();
        intent.setType("*/*");
        intent.setAction(Intent.ACTION_GET_CONTENT);
        startActivityForResult(Intent.createChooser(intent, "Select file"), LEARN_TREE);
} 

Then i got the uri from the intent of onActivityResult. First question here is why it displays a file named "servo.dat" as numbers (in this case it shows "5889")?

After that I put the uri as an extra into another intent and use that intent to start another activity. In the second activity I retrieve the uri. Now I'd like to use FileInputStream to read bytes from my file in order to write them to the ObjectOutputStream created from Socket.getOutputStream(). Here is where it doesn't work. Basically the path provided here

FileInputStream fis = new FileInputStream(uri.getPath());

is incorrect. If I check on my device the file location is Download/servo.dat, the Uri in the app shows Download/5889 and the absolute path that I tried retrieving using a UriUtils library found online shows storage/emulated/0/Download/servo.dat but this one doesn't actually exist on my phone.

I think it's not so hard but I'm getting confused since I'm new to both Android app development and Android itself, please help!

I'm open to any good solution, I saw online there is the ContentResolver class that should be helpful but I didn't manage to understand how to use it :|