Java servlet中的大Json数据

I work with java servlets and I want to receive Big json data from client.

my client code is

 url: "http://localhost:8080/JsonTest/setJson",
 type: "POST",
 dataType: 'json',
 contentType: 'application/json',
 data:{json:str},

my server code is

String json=request.getParameter("json");

but json variable is null

Can anybody help me?

try JSON.stringify on the data:

url: "http://localhost:8080/JsonTest/setJson",
type: "POST",
dataType: 'json',
contentType: 'application/json',
data: JSON.stringify({json:str}),

or if str is already a json string:

url: "http://localhost:8080/JsonTest/setJson",
type: "POST",
dataType: 'json',
contentType: 'application/json',
data: str,