使用Ajax实现检查用户名是可用
Ajax一个常用的地方就在于各大网站上注册时，检查用户名是否已经使用，下面我们就来简单的模拟一下这个功能：
先将html代码给出
<script type="text/javascript">var xmlHttp;function check(name){if(window.ActiveXObject){xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");}else if(window.XMLHttpRequest){xmlHttp=new XMLHttpRequest();}if(xmlHttp!=null){xmlHttp.open("POST", "LoginServlet", true);xmlHttp.onreadystatechange=function(){if(xmlHttp.readyState==4 && xmlHttp.status==200){var txt=xmlHttp.responseText;alert(txt);if(txt=="OK"){document.getElementById("hip").innerHTML="可以使用";}else{document.getElementById("hip").innerHTML="不可以使用";}}}xmlHttp.setRequestHeader("Content-type","application/x-www-form-urlencoded");xmlHttp.send("name="+name);}}</script> </head> <body> <input type="text" name="name" id="name"><br> <input type="submit" onclick="check(document.getElementById('name').value)"><br> <div id="hip"></div> </body></html>
给出一个登陆的Servlet
public class LoginServlet extends HttpServlet{public void destroy(){super.destroy(); // Just puts "destroy" string in log// Put your code here}public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException{response.setContentType("text/html");PrintWriter out = response.getWriter();out.flush();out.close();}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException{response.setContentType("text/html");PrintWriter out = response.getWriter();String name=request.getParameter("name");System.out.println("name===>"+name);if(name.equals("gavin")){out.print("OK");}else{out.print("NO");}out.flush();out.close();}public void init() throws ServletException{// Put your code here}}上面的代码中，如果在文本框中输入“gavin”，那么用户名可以使用，如果输入其他，则不能使用，非常简单，仅仅为了练习使用Ajax而已