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Editorial Team
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Asked: 2026-06-18T13:37:08+00:00

I have this ajax call from a javascript file and I want to pass

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I have this ajax call from a javascript file and I want to pass as a parameter the id of the user that I want to delete:

function eliminaUtente(id,nome){
if (confirm("Sei sicuro di voler eliminare l'utente "
    + nome
    + "?")) {
var xmlHttp2 = new XMLHttpRequest();
xmlHttp2.open("POST", "EliminaUtente", true);
xmlHttp2.setRequestHeader("Content-type",
        "application/x-www-form-urlencoded");
var params2 = "id=" + id;
xmlHttp2.send(params2);
xmlHttp2.onreadystatechange = function() {
    if (xmlHttp2.readyState == 4) 
    {
                    alert(xmlHttp2.status);  <-----------this prints always 0!
        if (xmlHttp2.status == 200) //
        {
            alert("utente eliminato!");
        } else {
            alert("An error occurred while communicating with server.");
        }
    }
};

}
}

in the correspondant Servlet called EliminaUtente i have this code:

  protected void doPost(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    String id = request.getParameter("id");
    System.out.println(id);
    String query = "delete from utente where idutente=" + id;
    System.out.println(query);
    try {
        Class.forName("com.mysql.jdbc.Driver").newInstance();

        Connection con = DriverManager
                .getConnection("jdbc:mysql://localhost/Spinning?user=root");
        PreparedStatement prest = con.prepareStatement(query);
        prest.executeUpdate();

        response.setContentType("text/plain");
        PrintWriter ajaxWriter = response.getWriter();
        ajaxWriter.print("ok");
        ajaxWriter.flush();
        ajaxWriter.close();

        con.close();
    } catch (Exception e) {
        e.printStackTrace();
        response.setContentType("text/plain");
        PrintWriter ajaxWriter = response.getWriter();
        ajaxWriter.print("ko");
        ajaxWriter.flush();
        ajaxWriter.close();
    }

}

}

I can’t understand where is the problem…can you help me please? 😉

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1 Answer

  1. Editorial Team

    I try your code and change a little bit i want to explain what did i and what i learn from it.I read some source. First i read XMLHttpRequest object and onreadyState event.
    I implement your example both PUT and GET action method.

    web.xml

    <?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    version="2.5">

    <servlet>
        <servlet-name>testServlet</servlet-name>
        <servlet-class>com.test.testServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>testServlet</servlet-name>
        <url-pattern>/test/*</url-pattern>
    </servlet-mapping>

</web-app>

    testServlet.java

    package com.test;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class testServlet extends HttpServlet {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        /*super.doPost(req, resp);*/
        String strId = req.getParameter("id");
        System.out.println(strId);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        //super.doGet(req, resp);
        String strId = req.getParameter("id");
        System.out.println(strId);
    }
}

    and main part NewFile.jsp

    <%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <input type="button" value="Submit" onclick="eliminaUtente('1')" width="100%" />
</body>
<script language="javascript" type="text/javascript">
    function eliminaUtente(id) {

        var xmlHttp = new XMLHttpRequest();
        var url = "test/NewFile.jsp?id=" + id;
        xmlHttp.open("POST", url, true);
        xmlHttp.send(url);
        xmlHttp.onreadystatechange = function() {
            if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
                alert("utente eliminato!");
            } else {
                alert("An error occurred while communicating with server.");
            }
        };
    }
</script>
</html>

    with this way i write the parameter 1(i hardcode it in jsp file method invoke) and write it to console, the first thing in here the difference your code and mine i remove the xmlHttp2.setRequestHeader("Content-type","application/x-www-form-urlencoded"); because if the method type is POST default encryption is this. 

    enctype = content-type [CI]
This attribute specifies the content type used to submit the form to the server (when the value of method is "post"). The default value for this attribute is "application/x-www-form-urlencoded". The value "multipart/form-data" should be used in combination with the INPUT element, type="file".
    • So no need to enctype default is OK for POST.
    • And this is open method signature open(method, url, async, user, password) here async is the parameter which means if it is false don’t wait a response from server implement the other line when response is come it will run. If it is true wait until response is come. Actually i try bot of them and it is worked.

    • Lastly i try it with GET. If you want use it with GET you should add xmlHttp2.setRequestHeader("Content-type","application/x-www-form-urlencoded"); code for encryption and remove the url parameter from send() method.

      function eliminaUtente(id) {

          var xmlHttp = new XMLHttpRequest();
    var url = "test/NewFile.jsp?id=" + id;
    xmlHttp.open("GET", url, true);
        xmlHttp2.setRequestHeader("Content-type","application/x-www-form-urlencoded");
    xmlHttp.send();
    xmlHttp.onreadystatechange = function() {
        if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
            alert("utente eliminato!");
        } else {
            alert("An error occurred while communicating with server.");
        }
    };
}

    Note: I try this code in firefox, i create xmlHttpRequest object. For all browser(include IE6) sure you know use:

    var xmlhttp;
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
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