request.getParameter始终返回null

如何解决request.getParameter始终返回null

我在从事离子应用程序。当用户登录时，具有不同信息的文件将发送到服务器。

let datos = this.getInfoLogin();

方法内容如下

getInfoLogin(): any {
    let datos = {
        "version": this.versionNumber,"user": this.loginGroup.value.user,"fechaLogin": this.getCurrentDate(),"password": this.loginGroup.value.password
    };

    return datos;
}

我通过有角度的邮政服务将该代码发送到服务器

this.http.postLogin(datos).subscribe(respLogin => {});

http.service.ts

@Injectable({
providedIn: 'root'
})
export class HttpService {

private url = 'http://localhost:8085/nombreApp/LoginServlet';

// Http Headers
headers: HttpHeaders = new HttpHeaders({
    Accept: "application/json","Content-Type": "application/json; charset='utf-8'",});

constructor(public http: HttpClient) {
    console.log("Servicio login listo");
}

postLogin(login): Observable<any> {
    return this.http.post(`${this.url}`,login,{ headers: this.headers });
}
}

但是在服务器上，使用时我总是得到null

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

LoginServlet.java

@Override
protected void doPost(HttpServletRequest request,HttpServletResponse response)
        throws servletexception,IOException {

    try {
        response.setContentType("text/html");
        String user = request.getParameter("user");
        
    } catch (Exception e) {
        LOGGER.log(Level.SEVERE,"Error PrintWriter." + e.getMessage());
    }

}

我知道数据已到，但我不知道如何读取。我究竟做错了什么？我已经搜索了很多，我发现正确的方法是这样。我是对的吗？