java - how to establish connections between a servlet and a socket -

supposing have servlet reads , writes file socket , want establish connection between servlet , socket, how done?

well, socket, read somewhere 1 has this:

url url  = new url("http://example.com/getfile"); urlconnection con = url.openconnection(); con.setdooutput(true); 

how same servlet?

i wanted since sending , receiving files between servlet , scoket. also, how both of them know when other has sent file , should read it?

i have searched can't find site explains it.

i unsure mean 'socket'. if socket standard protocol (http/https/ftp) can use above piece of code in servlet use in stand alone program.
if socket not prescribe standard might want open direct connection using below piece of code:

socket socket = new socket(server,port); //get input stream socket bufferedreader inputstream =       new bufferedreader(new inputstreamreader(                      socket.getinputstream()));  //get  output stream socket.  note // stream autoflush. printwriter outputstream =       new printwriter(new outputstreamwriter(                socket.getoutputstream()),true); outputstream.println("send_ data");       system.out.println(inputstream.readline());       socket.close(); 

regarding file sending piece of code, if primary task involved file transfer can use ftp protocol send files between servlet , socket.
can have file watcher on socket end know when file transferred. refer filewatcher , ftp more information.