使用Ajax从Servlet中的doGet获取参数

Question

I want to get the parameter from a input form which is set on my index.html:

GET:<br> 
<input type="text" size="20" id="name2" onblur="validate2()"  
     onFocus = "document.getElementById('msg2').innerHTML = ' '">
<div id = "msg">&nbsp</div>

On my servlet I want to get this parameter by request.getparameter("name2")

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("Get");
    System.out.println(request.getParameter("name2"));
    if(!request.getParameter("name2").equals("")) {
        numer = request.getParameter("name2");
        serviceConnection(request, response);
    }
}

but when I am starting my application the system.out.println is just printing the null variable.

On my ajaxvalidator javascript file I wrote this:

function validate2() {
var idField = document.getElementById("name2");
var data = "name2=" + encodeURIComponent(idField.value);
if (typeof XMLHttpRequest != "undefined") {
    req = new XMLHttpRequest();
} else if (window.ActiveXObject) {
    req = new ActiveXObject("Microsoft.XMLHTTP");
}
var url = "Validator"
req.open("GET", url, true);
req.onreadystatechange = inserter2
req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
req.send(data);

}

function inserter2() {
    if (req.readyState == 4) {
        if (req.status == 200) {
            var msg1 = req.responseText
            if (msg1 == "") {
                document.getElementById("msg").innerHTML = "<div style=\"color:red\">Wadliwa nazwa</div>";
                document.getElementById("org").value = '';
            } else {
                document.getElementById("org").value = msg1;
            }
        }
    }

How to solve this problem?

Answer 1

Your mistake is here:

req.open("GET", url, true);
// ...
req.send(data);

In HTTP GET, the data needs to go in request URL query string, not in request body. Sending data in request body works for POST only. The request URL query string is the part after ? in request URL.

So, this should do:

req.open("GET", url + "?" + data, true);
// ...
req.send();

Note that you can remove the request body content type header.

See also:

• doGet and doPost in Servlets
• Using java.net.URLConnection to fire and handle HTTP requests
• How to use Servlets and Ajax?