jsp：
<html:html lang="true">
<head>
<html:base />
<title> Ajax.jsp </title>
<script type="text/javascript">
var xmlHttp;
function createXMLHttpRequest() {
if (window.ActiveXObject) {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}
else if (window.XMLHttpRequest) {
xmlHttp = new XMLHttpRequest();
}
}
function startRequest() {
createXMLHttpRequest();
var url = " <%=request.getContextPath()%> /ajax.do?method=showTable";
xmlHttp.onreadystatechange = handleStateChange;
xmlHttp.open("POST", url, true);
xmlHttp.send(null);
}
function handleStateChange() {
if(xmlHttp.readyState == 4) {
if(xmlHttp.status == 200) {
showTable();
setInterval("startRequest();",2000);
}
}
}
function showTable(){
var xmlDoc=xmlHttp.responseXML;
var students=xmlDoc.getElementsByTagName("student");
var result=" <table border=1> <tr> <th> ID </th> <th> USERNAME </th> <th> PASSWORD </th> </tr > ";
for(var i=0;i <students.length;i++){
result +=" <tr> ";
var student=students
;
result
+=" <td> "+student.getElementsByTagName("id")[0].firstChild.nodeValue+" </td> ";
result
+=" <td> "+student.getElementsByTagName("username")[0].firstChild.nodeValue+" </td> ";
result
+=" <td> "+student.getElementsByTagName("password")[0].firstChild.nodeValue+" </td> ";
result +=" </tr> ";
}
result +=" </table> ";
document.getElementById('result').innerHTML=result; }
</script>
</head>
<body>
<html:form action="employee" method="post" focus="login">
<input type="button" value="Click" onClick="startRequest();" />
<div id="result"> </div>
</html:form>
</body>
</html:html>
ajax.do:
private static final Logger log=Logger.getLogger(AjaxAction.class);
public ActionForward showTable(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response) {
try{
System.out.println("end");
UserInfoBO bo=new UserInfoBO();
List list=bo.init();
response.setContentType("text/xml");
PrintWriter out=response.getWriter();
out.print(parasToXml(list));
}catch(Exception e){
log.error("显示表格错误"+e);
}
return null;
}
public String parasToXml(List list){
StringBuffer sb=new StringBuffer();
sb.append(" <?xml version=\"1.0\" encoding=\"GBK\" ?> ");
sb.append(" <sutdents> ");
for(int i=0;i <list.size();i++){
UserInfo info=(UserInfo)list.get(i);
sb.append(" <student> ");
sb.append(" <id> "+info.getId()+" </id> ");
sb.append(" <username> "+info.getUsername()+" </username> ");
sb.append(" <password> "+info.getPassword()+" </password> ");
sb.append(" </student> ");
}
sb.append(" </sutdents> ");
return sb.toString();
}
在showTable方法里面有一行System.out.println("end");
运行的时候在控制台上输出end的次数依次为1,1,2,4,6,10。。。
这里我就不是很明白，应该每次输出end的次数为2次，
第一次执行showTable时输出，第二次是执行 setInterval("startRequest();",2000);输出的
大概运行了20分站把，也没有报错，控制台也没有输出"end",相当与挺了
请问为什么会这样？
