ResponseText 为 null，即使它应该设置为 JavaScript

ResponseText is null even though it should be set JavaScript

本文关键字：JavaScript 设置 null ResponseText      更新时间：2023-09-26

我有一个大问题，我的代码中没有看到任何错误。 程序应从字段p1和p2中添加两个值，并将它们上传到站点，而无需重新加载整个页面。我用简单的javascript做了，但我想使用AJAX。一切都已经完成，但某处有小错误。

我你看validate()和insterter()，警报有适当的价值

 alert("data = "+data);
 req.send(data);

但来自Insterter的味精只是空的。我不知道为什么。请帮忙。我想更正此代码。

var msg = req.responseText;
        alert("msg = "+msg);

为什么味精为空的原因？ 

@WebServlet("/Serwlet")
public class Serwlet extends HttpServlet {
private static final long serialVersionUID = 1L;
static String KOD =
"<html>"+
"<head>"+
 "<meta http-equiv='"Content-Type'" content='"text/html; charset=windows-1250'">"+
"<title>Testowanie</title>"+
"<script type='"text/javascript'" language='"javascript'" src='"servletD2Script.js'"></script>"+
"</head>"+
"<body>"+
"<div id='"msg1'">Pierwsza suma</div>"+
"<div id='"msg2'">Pierwsza suma</div>"+
"<center><h2>Testowanie parametrów</h2></center>"+
"<hr>"+
"<form method='"get'" action='"Serwlet'">"+
"p1<input type='"text'" size='"50'" name='"p1'" onblur='"validate()'"><br>"+
"p2<input type='"text'" size='"50'" name='"p2'" onblur='"validate()'"><br>"+
"<br><input type='"submit'" value='"Wyślij formularz by GET'">"+
"</form>"+
"</hr>"+
"<hr>"+
"<form method='"post'" action='"Serwlet'">"+
"p3<input type='"text'" size='"50'" name='"p3'" onblur='"funkcja()'"><br>"+
"p4<input type='"text'" size='"50'" name='"p4'" onblur='"funkcja()'"><br>"+
"<br><input type='"submit'" value='"Wyślij formularz by POST'">"+
"</form>"+
"</hr>"+
"</body></html>";
public Serwlet() {
    super();
}
static boolean raz = true;
private void serviceRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
      response.setContentType("text/html");
      response.setHeader("Cache-Control", "no-cache");
      PrintWriter out = response.getWriter();
      if(raz){out.print(Serwlet.KOD);raz = false;}
      String name = request.getParameter("name");   // dostaję nazwisko
      String org = ""; //jakas wartosc 
      out.write(org != null ?  org : "");    // zwracam organizację lub pusty napis, jesli nie znam nazwiska
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    serviceRequest( request, response);
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    serviceRequest( request, response);
}
}

var req;
function validate() {
//var idField = document.getElementById("name");
var wrt1 = document.getElementById("p1").value;
var wrt2 = document.getElementById("p2").value;
var data = eval(wrt1)+eval(wrt2)+"";
if (typeof XMLHttpRequest != "undefined") {
    req = new XMLHttpRequest();
} else if (window.ActiveXObject) {
    req = new ActiveXObject("Microsoft.XMLHTTP");
}
var url = "Serwlet";
req.open("POST", url, true);      
req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
alert("data = "+data);
req.send(data);
req.onreadystatechange = inserter;
}


function inserter() {
if (req.readyState == 4) {
    if (req.status == 200) {
        var msg = req.responseText;
        alert("msg = "+msg);
        if (msg == "") {
            document.getElementById("msg1").innerHTML = "<div style='"color:red'">"+"MSG WAS EMPTY"+"</div>";
            //document.getElementById("msg1").value = "blabla";
        }
        else
            document.getElementById("msg1").innerHTML = "<div style='"color:red'">"+msg+"</div>";
            //document.getElementById("msg1").value = "COOOO JEST";
    }
}
}

这部分代码总是被调用，MSG 是 ">

if (msg == "") {
        document.getElementById("msg1").innerHTML = "<div style='"color:red'">"+"MSG WAS EMPTY"+"</div>";
        //document.getElementById("msg1").value = "blabla";
    }
raz似乎

只为真一次，所以下次你输入servlet时，你不要在if语句中输入，也不打印Serwlet.KOD。

那我不明白：

  String org = ""; //jakas wartosc 
  out.write(org != null ?  org : "")

它总是打印一个空字符串，这是没有用的。

此外，最好用 out.close(); 结束serviceRequest方法。

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