AJAX用户名异步校验

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<tr>   <th><span class="requiredField">*</span>用户名:</th>   <td><input type="text" id="username" name="username"class="text" maxlength="20" onblur="checkUsername()">   <span id="usernameSpan"></span>   </td></tr>

//AJAX用户名异步校验function checkUsername(){//获得文本框值:var username = document.getElementById("username").value;//1,创建异步交互对象var xhr = createXmlHttp();//2,设置监听xhr.onreadystatechange = function(){if(xhr.readyState == 4){if(xhr.status == 200){document.getElementById("usernameSpan").innerHTML = xhr.responseText;}}}//3,打开链接xhr.open("GET","${pageContext.request.contextPath}/user_findByName.action?time="+new Date().getTime()+"&username="+username,true)//4,发送xhr.send(null);}function createXmlHttp(){var xmlHttp;try{xmlHttp = new XMLHttpRequest();}catch(e){try{xmlHttp = new ActiveXobject("Msxm12.XMLHTTP");}catch(e){try{xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");}catch(e){}}}return xmlHttp;}

/** * Ajax进行异步校验用户名的执行方法 *  * @throws IOException */public String findByName() throws IOException {// 调用Service进行查询:User user = userService.findByUsername(model.getUsername());// 获得response对象,向页面输出HttpServletResponse response = ServletActionContext.getResponse();// response.setCharacterEncoding("text/html;charset=UTF-8");//错误response.setContentType("text/html;charset=UTF-8");// 判断if (user != null) {// 查询到该用户:用户名已经存在response.getWriter().println("<font color='red'>用户名已经存在</font>");} else {// 没查询到该用户:用户名可以使用response.getWriter().println("<font color='green'>用户名可以使用</font>");}return NONE;

UserDao

public User findByUsername(String username) {List<User> list = getSession().createQuery(//"from User u where u.username = ?")//.setParameter(0, username)//.list();if (list != null && list.size() > 0) {return list.get(0);}return null;}

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