Ajax入门示例

    技术2022-05-12  0

    第一个Ajax入门示例,注册页面,当输入用户名时,异步发送请求验证用户名是否可以用。

    JSP页面代码如下:

     

    <html>  <head>        <title>第一个Ajax示例,验证用户名是否使用</title> <script type="text/javascript">   /* Create a new XMLHttpRequest object to talk to the Web server */  var xmlHttp = false;  /*@cc_on @*/  /*@if (@_jscript_version >= 5)  try {    xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");  } catch (e) {    try {      xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");    } catch (e2) {      xmlHttp = false;    }  }  @end @*/    if (!xmlHttp && typeof XMLHttpRequest != 'undefined') {    xmlHttp = new XMLHttpRequest();  }    function callServer() {      var username = document.getElementById("username").value;     if ((username == null) || (username == "")) return;    var url = "servlet/UsernameServlet?username="+escape(escape(username));    xmlHttp.open("GET", url, true);    xmlHttp.onreadystatechange = updatePage;    xmlHttp.send(null);  }    function updatePage() {     if (xmlHttp.readyState == 4 ) {      if(xmlHttp.status ==200){               var response = xmlHttp.responseText;        alert(response);        document.getElementById("msg").innerHTML = response;/*        alert("headers:"+xmlHttp.getAllResponseHeaders());        alert("Content-Length:"+xmlHttp.getResponseHeader("Content-Length"));        alert("Content-Type:"+xmlHttp.getResponseHeader("Content-Type"));        alert("Date:"+xmlHttp.getResponseHeader("Date"));        alert("Server:"+xmlHttp.getResponseHeader("Server"));*/       }else{        alert("status:"+xmlHttp.status);       }   }  } </script>  </head>      <body> <form action="servlet/UsernameServlet" method="post">  <p>用户名: <input type="text" name="username" id="username" size="25"         onChange="callServer();" /><span id="msg"></span></p>  <p>密码: <input type="text" name="pwd"  size="25"/></p>  <p><input type="submit" value="注册" />  </p> </form>  </body></html>

     

    UsernameServlet代码如下:

     

      response.setContentType("text/html");  response.setCharacterEncoding("UTF-8");  PrintWriter out = response.getWriter();  String username = request.getParameter("username");  username = unescape(username);  if (username.equals("东东")) {   out.print("此用户名已经被使用了,请输入其它名字");  } else {   out.print("此用户名没有被使用");  }

      out.flush();  out.close();

     

    处理传递中文参数乱码的方法unescape(String str)如下:

     

     public String unescape(String src) {  // if (StringUtil.checkBlank(src).equals("")) {  // return "";  // }  StringBuffer tmp = new StringBuffer();  tmp.ensureCapacity(src.length());  int lastPos = 0, pos = 0;  char ch;  while (lastPos < src.length()) {   pos = src.indexOf("%", lastPos);   if (pos == lastPos) {    if (src.charAt(pos + 1) == 'u') {     ch = (char) Integer.parseInt(src       .substring(pos + 2, pos + 6), 16);     tmp.append(ch);     lastPos = pos + 6;    } else {     ch = (char) Integer.parseInt(src       .substring(pos + 1, pos + 3), 16);     tmp.append(ch);     lastPos = pos + 3;    }   } else {    if (pos == -1) {     tmp.append(src.substring(lastPos));     lastPos = src.length();    } else {     tmp.append(src.substring(lastPos, pos));     lastPos = pos;    }   }  }  return tmp.toString(); }

     

     


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