I am writing an application using java technology.
Its a web application.
A social networking web site.
Need advice regarding its security?
What aspects do I need to keep in mind? A secured URL is just to encrypt the communication between client (browser) and server. What other aspects like security against cross site scripting, SQL Injection do I need to take into consideration while designing the application?
Security isn't something that can bolted onto an app once it's done; it needs to be considered from the start for all of its aspects. Start reading here: http://www.coderanch.com/how-to/java/SecurityFaq#web-apps. Also consider the non-code aspects like security at the hosting center, malicious users, etc.