The following two pages describe an Ajax call, including how to create an XMLHTTPRequest object, how to send requests to the server, and how to receive server responses and asynchronous calls. This is a good example of getting started with Ajax.
The first page:
<% @ Page contenttype = "text/html; charset = gb2312" %>
<HTML>
<Head>
<Meta http-equiv = "Content-Type" content = "text/html; charset = gb2312">
<Title> Ajax Entry Example </title>
<Script language = "JavaScript">
VaR http_request = false;
Function send_request (URL, poststr) {// initialize, specify the processing function, and send the request Function
Http_request = false;
// Start initializing the XMLHTTPRequest object
If (window. XMLHttpRequest) {// Mozilla Browser
Http_request = new XMLHttpRequest ();
If (http_request.overridemimetype) {// sets the mime category
Http_request.overridemimetype ('text/xml ');
}
}
Else if (window. activexobject) {// IE browser
Try {
Http_request = new activexobject ("msxml2.xmlhttp ");
} Catch (e ){
Try {
Http_request = new activexobject ("Microsoft. XMLHTTP ");
} Catch (e ){}
}
}
If (! Http_request) {// exception. An error occurred while creating the object instance.
Window. Alert ("the XMLHTTPRequest object instance cannot be created .");
Return false;
}
Http_request.onreadystatechange = processrequest;
// Determine the request sending method and URL and whether to execute the following code synchronously
Http_request.open ("Post", URL, true );
Http_request.setrequestheader ("Content-Type", "application/X-WWW-form-urlencoded ");
Http_request.send (poststr );
}
// Function for processing the returned information
Function processrequest (){
If (http_request.readystate = 4) {// judge the object status
If (http_request.status = 200) {// The information has been returned successfully. Start to process the information.
Alert (http_request.responsetext );
} Else {// The page is abnormal.
Alert ("the page you requested has an exception. ");
}
}
}
Function form_submit (){
VaR F = Document. form1;
VaR username = f. username. value;
VaR Password = f. Password. value;
VaR poststr = "";
If (username = ""){
Window. Alert ("the user name cannot be blank. ");
F. username. Focus ();
Return false;
}
If (Password = ""){
Window. Alert ("the password cannot be blank. ");
F. Password. Focus ();
Return false;
}
Poststr = "username =" + encodeuri (F. username. Value) + "& Password =" + F. Password. value;
Send_request ('form _ HANDLE. jsp ', poststr );
Return false;
}
</SCRIPT>
</Head>
<Body>
<Form name = "form1" method = "Post" Action = "" onsubmit = "Return form_submit ()">
<Table width = "300" border = "0" cellspacing = "4" cellpadding = "0" style = "font-size: 12pt;">
<Tr>
<TD width = "74" Height = "25"> User name: </TD>
<TD width = "220" Height = "25"> <input name = "username" type = "text" id = "username" size = "20"> </TD>
</Tr>
<Tr>
<TD Height = "25"> password: </TD>
<TD Height = "25"> <input name = "password" type = "password" id = "password" size = "20"> </TD>
</Tr>
<Tr align = "center">
<TD Height = "25" colspan = "2"> <input type = "Submit" name = "Submit" value = "Submit"> </TD>
</Tr>
</Table>
</Form>
</Body>
</Html>
Second page, request processing page:
<% @ Page contenttype = "text/html; charset = gb2312" Language = "Java" errorpage = "" %>
<%
String username = new string (request. getparameter ("username"). getbytes ("ISO-8859-1"), "utf8 ");
String Password = new string (request. getparameter ("password"). getbytes ("ISO-8859-1"), "utf8 ");
System. Out. println ("username:" + username );
System. Out. println ("Password:" + password );
Out. println ("the username and password are:" + username + "[" + password + "]");
%>
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