Finally, I got the mistake and the reason was I need to stringify the JSON data I was sending. I have to set the content type and datatype in XHR object. So the correct version is here:
$.ajax({
type: 'POST',
url: "http://localhost:8080/project/server/rest/subjects",
data: JSON.stringify({
"subject:title":"Test Name",
"subject:description":"Creating test subject to check POST method API",
"sub:tags": ["facebook:work", "facebook:likes"],
"sampleSize" : 10,
"values": ["science", "machine-learning"]
}),
error: function(e) {
console.log(e);
},
dataType: "json",
contentType: "application/json"
});
May be it will help someone else.