Call Web Service method that insert an object from jquery ajax - json

Question

I have a web service method similiar to this:
#Path("/insert_update")
#POST
#Consumes({ MediaType.APPLICATION_JSON })
#Produces({ MediaType.APPLICATION_JSON })
public Object insert(User obj) {
...(insert and return object)
}
And I want to call this method from jquery, using ajax. I've tried something like this:
var rootURL = "http://Path/to/my/web/service";
function insertUpdate() {
var user = {'name' : $("#name").val(),
'surname' : $("#surname").val(),
'surname1' : $("#surname1").val(),
'usertxt' : $("#usertxt").val(),
'password' : $("#password").val() };
$.ajax({
url : rootURL + "/insert_update",
type : "POST",
contentType: 'json',
dataType : "json",
data : user,
success : function(data) {
alert(JSON.stringify(data));
},
error : function(data) {
}
});
}
Is this code correct? When I try to use it I get this response:
Failed to load resource: Request header field Content-Type is not allowed by Access-Control-Allow-Headers.
XMLHttpRequest cannot load ... . Request header field Content-Type is not allowed by Access-Control-Allow-Headers.
I hope you can help me.
Greetings.
UPDATE
The web service is in the same machine, but in other port. I run the web service project on a WebSphere Application Server and then I only open the HTML file to test my code.
I have other method I don't have problem with, like this:
#Path("/all")
#GET
#Produces(MediaType.APPLICATION_JSON)
public Object all() {
...(get all users)
}
And the JQuery method for this code:
function all() {
$.ajax({
url : rootURL + "/all",
type : "GET",
dataType : "json",
success : function(data) {
$("#tabla tbody:last").empty();
$.each(data.data, function(i, item) {
$("#tabla tbody:last").append("<tr><td>"+item.id+"</td><td>"+item.name+
"</td><td>"+item.surname+"</td><td>"+item.surname1+"</td><td>"
+item.usertxt+"</td><td>"+item.password+"</td></tr>");
});
},
error : function(data) {
}
});
}
This works fine, I have no problem...but I had to donwload an extension for Chrome to test locally, Allow-Control-Allow-Origin.
Why with GET method I have no problem and with POST method yes???
Greetings.