@WebServlet(name = "registration servlet", urlPatterns = "/register")
public class Register extends HttpServlet{

PrintWriter output;
private final static int EMPTY = 0;
private static int byteContainer = 0;
private static int lines = 0;
private static String charContainer = "";

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    output = resp.getWriter();
    output.print("The Do Get METHOD");

}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    output = resp.getWriter();

    ServletInputStream servletInputStream = req.getInputStream();

    if(servletInputStream.isReady()){

        byte [] bytes = new byte[4096];

        while((byteContainer = servletInputStream.read()) != -1){

            bytes [lines] = (byte)byteContainer;
            lines++;

            if((servletInputStream.read()) == -1){

                char [] chars = new char[4096];

                for(int  i = 0, k = 0 ; i < lines; i++, k++){

                    chars[i] = (char) bytes [k];
                    charContainer += chars[i];
                }
            }
        }
    }

    lines = EMPTY;
    output.print(charContainer);
    servletInputStream.close();

Запрос Ajax:

$("#register-button").click(function () {

var user = {

    firstName:$("#first-name").val(),
    lastName:$("#last-name").val(),
    nickName:$("#nick_name").val(),
    email:$("#email_").val(),
    password:$("#password_").val(),
    customerType:$("#cust-type").val()
}

console.log(user);

var JSONString = JSON.stringify(user);

var JSONObject = JSON.parse(JSONString);

console.log(JSONObject);

var url = "http://localhost:8080/CouponProject/register";

$.ajax({

    url:url,
    method:"post",
    data:JSONObject,
    contentType:"application/json",
    error:function (message) {
        console.log(message+" In the error function!")
    },
    success:function (data) {

        console.log(data);

    },
    headers:
    {
        "Accept":"application/json",
        "Accept-Language":"en",
        "Cache-Control":"max-age=3600"
     }
  });

});