I can’t send the simplest request to the servlet using jQuery. But at the same time, if I send through the form, then everything works with a bang.
Below is the index.html from which I want to send the username. login.js, in which I form the request itself, SerletStore.java the servlet itself. And the structure of the whole project.

login.js
The only more or less working url = “http: // localhost: 8080 / testservlet / post “, and they “/ testservlet / post”, “testservlet / post”, “/ post,” “post” cause a 404 error.

function addNewVoting () {
    var xhr = new XMLHttpRequest ();
    var body = 'name =' + encodeURIComponent ("name") +
     '& amp; surname =' + encodeURIComponent ("surname");
    xhr.open ("POST", 'http: // localhost: 8080 / testservlet / post', true)
    xhr.setRequestHeader ('Content-Type', 'application / x-www-form-urlencoded')
    xhr.send (body);
  };
  function addNewVoting1 () {
    var user = {
      "firstName": "vlad"
    }
    var JSONString = JSON.stringify (user);
    var url = "http: // localhost: 8080 / testservlet / post";
    $ .ajax ({
      url: url,
      method: "post",
      data: JSONString,
      contentType: "application / json",
      error: function (message) {
        var JSONObject = JSON.parse (message);
        console.log (JSONObject);
      },
      success: function (data) {
        var JSONObject = JSON.parse (data);
        console.log (JSONObject);
      },
      headers: {
        "Accept": "application / json",
        "Accept-Language": "en",
        "Cache-Control": "max-age = 3600"
      }
    });
  };

When the second function is called, it outputs this:

index.html

& lt;! DOCTYPE html & gt;
& lt; html & gt;
& lt; head & gt;
  & lt; meta charset = "UTF-8" & gt;
  & lt; title & gt; Login Form & lt; / title & gt;
  & lt; link rel = "stylesheet" href = "css / login.css" & gt;
  & lt; link rel = "stylesheet" href = "http://fonts.googleapis.com/css?family=Open+Sans:400,700" & gt;
  & lt; script src = "https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js" & gt; & lt; / script & gt;
  & lt; script src = "/ js / login.css" & gt;
  & lt; / script & gt;
& lt; / head & gt;
& lt; body & gt;
& lt; div id = "login" & gt;
  & lt; form id = "form" name = "form-login" & gt; & lt;! - action = "store" method = "POST" & gt; - & gt;
    & lt; span class = "fontawesome-user" & gt; & lt; / span & gt;
    & lt; input type = "text" id = "user" name = "username" placeholder = "Username" & gt;
    & lt; span class = "fontawesome-lock" & gt; & lt; / span & gt;
    & lt; input type = "password" id = "pass" name = "password" placeholder = "Password" & gt;
    & lt; input type = "input" id = "login-submit" value = "Login" & gt;
  & lt; / form & gt;
  & lt; input style = "margin-left: 30px; margin-top: 10px" type = "button" onclick = "addNewVoting ()" value = "TAKE" / & gt;
& lt; / div & gt;
& lt; / body & gt;
& lt; / html & gt;

ServletStore.java

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
@WebServlet (name = "post", urlPatterns = "/ post")
public class Servlet extends HttpServlet {
  @Override
  protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    PrintWriter writer = resp.getWriter ();
    writer.print ("Hello");
  }
  @Override
  protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    super.doPost (req, resp); 
}
}

Project Structure :

Another screenshot might help:

I also experimented with contentType, and either I did it wrong, or nothing works either. Please help !!!

Answer 1, authority 100%

In the doPost () method of your servlet, you only call the doPost () of the abstract parent class HttpServlet, which means that your servlet does not actually have a post request handler. But it is the post request that you send from the script. That is why you get a 405 “Method not supported” error.

Besides, I see that you have already messed up a lot in the script. Decide how you want to send data from the script to the servlet. A simpler option is in the form of query parameters. Then the script will look like this:

var userObj = {
  "userName": "vlad"
}
var url = "http: // localhost: 8080 / test / post";
$ .ajax ({
  url: url,
  method: "post",
  data: userObj,
  error: function (message) {
    console.log (message);
  },
  success: function (data) {
    console.log (data);
  }
});

And the doPost () method of the servlet is like this:

@ Override
protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  String userName = req.getParameter ("userName");
  if (userName == null || "" .equals (userName.trim ())) {
    userName = "Anonymous";
  }
  String greetings = "Hello" + userName;
  resp.setContentType ("text / plain");
  resp.getWriter (). write (greetings);
}

If sent as JSON data, then the script will be like this:

var userObj = {
  "userName": "vlad"
}
var userJson = JSON.stringify (userObj);
var url = "http: // localhost: 8080 / test / post";
$ .ajax ({
  url: url,
  method: "post",
  data: userJson,
  contentType: "application / json",
  error: function (message) {
    console.log (message);
  },
  success: function (data) {
    console.log (data);
  }
});

And the code of the doPost () method will become much more complicated and require dependencies to work org.json.json :

@ Override
protected void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  String userName = "Anonymous";
  StringBuffer sb = new StringBuffer ();
  String line = null;
  BufferedReader reader = req.getReader ();
  while ((line = reader.readLine ())! = null)
    sb.append (line);
  try {
    JSONObject jsonObject = new JSONObject (sb.toString ());
    userName = jsonObject.getString ("userName");
  } catch (JSONException e) {
    // throw new IOException ("Error parsing JSON request string");
  }
  String greetings = "Hello" + userName;
  resp.setContentType ("text / plain");
  resp.getWriter (). write (greetings);
}