Hi Bujji, 


See the links below for further related information. 

http://blogs.developerforce.com/developer-relations/2012/02/quick-tip-public-restful-web-services-on-force-com-sites.html


http://salesforce.stackexchange.com/questions/15578/restrequest-requestbody-instead-of-params


sounds like a job for the REST API, have a look here http://www.salesforce.com/us/developer/docs/apexcode/index_Left.htm#StartTopic=Content/apex_rest_code_sample_basic.htm

depending on the complexity of your JSON object you might be able to archive this by passing the values via apex:actionFunction and apex:param

have a look here: http://boards.developerforce.com/t5/Apex-Code-Development/How-do-I-pass-value-of-apex-inputField-to-Custom-Controller/td-p/532905

In a previous project I was working with a quite complex JSON object and tried to pass it via function and param to the Controller, but it was always null for the controller. I found a workaround by saving the JSON object in a Note record via API and just passing the Note ID to the controller

http://salesforce.stackexchange.com/questions/13026/how-to-get-the-parameters-coming-from-webhook-post-api

https://developer.atlassian.com/display/JIRADEV/JIRA+Webhooks+Overview


Regards,
Ashish