i'm a newbie with RPi and i'm still discovering its features. I've installed tornado web server on RPi and connected the pi with arduino board. the server just receives a character (represents a command) and forward it to arduino over serial. my question is: Is there any way or program for windows i can use to send this character command to the web server on RPi?
You can use PHP to do this. Program it in such a way that you can send GET requests to the webpage (i.e.
http://raspberrypi:80/arduinocontrol.php?char=x), then it forwards your character to the Arduino.
Of course, I assume you have already worked out the Raspberry Pi to Arduino communication step already, since your question merely asks 'how can I send characters to my web server?'
You can try using Node-RED. With Node-RED, you can send command to your Arduino through the web, by email or by Twitter.
Look at this tutorial on how to get Node-RED installed. I would recommend starting off with a fresh image of Raspbian. There's a bit of setup involved.
The tutorial doesn't explain everything on what you need to do to get your work accomplished. You'll have to do some poking around yourself, but this is the surest way to do it. I'd love to help you with more specific instructions. However, I do not have an Arduino near me right now.