Use 10.0.2.2 instead of localhost.
If you are referring to a localhost from your device than use the http://10.0.2.2/ instead of the http://127.0.0.1/ or http://localhost/.
Because your Android emulator is running on a Virtual Machine(QEMU) and you can not connect to a server directly running on your PC.
So your code snippet will be like this:
HttpPost httpMethod = new HttpPost("http://10.0.2.2:8080/getHeader/HeaderServlet");
Refer this : Emulator Networking for more information.