Ajax实现动态刷新页面（get）

function getXmlHttpRequest() {
var xhr;

try {
// Firefox, Opera 8.0+, Safari
xhr = new XMLHttpRequest();
} catch (e) {

// Internet Explorer
try {
xhr = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {

try {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e) {
alert("您的浏览器不支持AJAX！");
return false;
}
}
}
return xhr;
}

<script type="text/javascript">
window.onload = function () {
document.getElementById("name_r").onblur = function () {
var name = document.getElementById("name_r").value;

//                发出异步请求
var xhr = getXmlHttpRequest();
xhr.onreadystatechange = function () {
if (xhr.readyState == 4) {
if (xhr.status == 200) {
//获取响应正文
document.getElementById("msg").innerHTML = xhr.responseText;
}
}
}
var url = "/servlet/CheckServlet?name_r=" + name + "&time=" + new Date().getTime();
xhr.open("GET", url, true);
xhr.send(null);
}
}
</script>

request.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=utf-8");
BusinessService s = new BusinessServiceImpl();
String username =  request.getParameter("name_r");
if (username!=null){
PrintWriter pw = null;
try {
pw = response.getWriter();
} catch (IOException e) {
e.printStackTrace();
}
List<Author> authors =  s.listAuthors();
List names = new ArrayList();
for (Author authors1:authors){
names.add(authors1.getUsername());
}
if (names.contains(username)){
pw.write("<font color='red'>用户名呢已经存在</font>");
}else {
pw.write("<font color='green'>用户名可以使用</font>");
}
}