@Override
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setHeader("Access-Control-Allow-Origin", "*");//允許所有，不安全
    response.setHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
    response.setHeader("Access-Control-Allow-Methods", "GET, POST, PUT");
    response.setHeader("Access-Control-Allow-Credentials", "true");
    super.service(request, response);
}
 

$.ajax({
url: “http://xxxx.xxxx.com/api/user/login“,
type: “post”,
dataType: “text”,
contentType: “application/json”,
data: JSON.stringify(data),
headers: {‘Content-Type’: ‘application/json’},
success: function (res) {
alert(res);
}
})