Web Scraping

So, lets suppose you are trying to login into www.addic7ed.com. These are the
headers that were captured by the Live Http Header addon
-------------------------------------------------------------------------------------------------------------------
[I am just mentioning the relevant ones]
-------------------------------------------------------------------------------------------------------------------
1)POST /dologin.php HTTP/1.1
2)User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:7.0.1) Gecko/20100101 Firefox/7.0.1
3)Referer: http://www.addic7ed.com/login.php
4)Cookie: PHPSESSID=ff39a25af0d71e6535d946b454dd94
5)username=ranveer5289&password=mypasswordissecret&Submit=Log+in

So, if you take a look the 5th header is the important one.
Therefore first try to send this header using

Document doc = Jsoup.connect("http://www.addic7ed.com/login.php").data("username", "ranveer5289",
"password",   "mypasswordissecret","Submit","Log+in").post();

If than also you are not able to login than your site need cookies in the request
to be send by your Java code.

Document doc = Jsoup.connect("http://www.addic7ed.com/login.php").data("username", "ranveer5289",
"password","mypasswordissecret","Submit","Log+in").cookie("PHPSESSID","ff39a25af0d71e6535d946b454dd94").post();

for some website you may also need to set Referer and User-Agent.