The current status of the XmlHttpRequest object is 0

Question

The current status of the XmlHttpRequest object is 0

In my JavaScript file, I have an AJAX call where I need to pass the user's ID as a parameter for deletion:

function deleteUser(id, name){
if (confirm("Are you sure you want to delete user "
    + name
    + "?")) {
var xmlHttp2 = new XMLHttpRequest();
xmlHttp2.open("POST", "DeleteUser", 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("User deleted!");
        } else {
            alert("An error occurred while communicating with server.");
        }
    }
};

} }

Within the corresponding servlet named DeleteUser, the following code is implemented:

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 user where user_id=" + id;
    System.out.println(query);
    try {
        Class.forName("com.mysql.jdbc.Driver").newInstance();

        Connection con = DriverManager
                .getConnection("jdbc:mysql://localhost/Database?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'm facing some issues and can't seem to figure out what's wrong. Can someone assist me with this problem? ;)

java javascript ajax servlets xmlhttprequest

Answer 1

Answer №1

I experimented with your code and made some modifications to explain what I did and what I learned from it. I delved into sources about the XMLHttpRequest object and the onreadystatechange event. I successfully implemented both the PUT and GET action methods in your example.

In the web.xml file:

<?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>

In 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 the 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>
... (truncated for brevity) ...

Overall, while working on this code, I discovered that specifying the encryption type in the POST method as

application/x-www-form-urlencoded

is unnecessary, as it defaults to that value. Moreover, understanding the significance of the async parameter in the open() method allowed me to experiment with different responses from the server.

... (truncated for brevity) ...

Answer 2

I experimented with your code and made some modifications to explain what I did and what I learned from it. I delved into sources about the XMLHttpRequest object and the onreadystatechange event. I successfully implemented both the PUT and GET action methods in your example.

In the web.xml file:

<?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>

In 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 the 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>
... (truncated for brevity) ...

Overall, while working on this code, I discovered that specifying the encryption type in the POST method as

application/x-www-form-urlencoded

is unnecessary, as it defaults to that value. Moreover, understanding the significance of the async parameter in the open() method allowed me to experiment with different responses from the server.

... (truncated for brevity) ...

Answer 3

Answer №2

spelling mistake?

alert(xmlHttp2.status); <-----------this consistently displays 0! It now says "2'

Answer 4

spelling mistake?

alert(xmlHttp2.status); <-----------this consistently displays 0! It now says "2'

Answer 5

Answer №3

The issue arose when I needed to insert the value "false" in the following line:

xmlHttp2.open("POST", "EliminaUtente", FALSE);

Answer 6

The issue arose when I needed to insert the value "false" in the following line:

xmlHttp2.open("POST", "EliminaUtente", FALSE);

The current status of the XmlHttpRequest object is 0

Answer №1

Answer №2

Answer №3

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