Ajax used to determine whether a user exists

The Ajax (JavaScript) function of the registration page is used to determine whether a user exists, so that the page Passes parameters from the background without refreshing the page. <SCRIPT type = "text/JavaScript">
VaR http_request = false;
VaR is_open = false;

Function callserver (){

VaR user = Document. getelementbyid ("username"). value;
If (user = NULL) | (user = "") return false;

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
VaR url = "http: // localhost: 8086/bayestore/ajax. jsp? Username = "+ user;
Http_request.open ("get", URL, false );
Http_request.send (null );


}

// 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.
Document. getelementbyid ("checkuser"). value = http_request.responsetext;
Alert (http_request.responsetext );
} Else {// The page is abnormal.
Alert ("the page you requested has an exception. ");
}
}
}
</SCRIPT>

Register the JSP form tag on the page

<Form action = "register. Do" name = "userregister" method = "Post">

<Table width = 750 border = 0 cellpadding = 3 cellspacing = 0 bgcolor = "# f3f9ff">

<Tbody>
<Tr>
<TD colspan = 5 Height = 5> </TD> </tr>
<Tr>
<TD width = 60 Height = 25>
<Div align = right> * </div> </TD>
<TD width = 92 Height = 25> User name: </TD>
<TD width = 172 Height = 25> <input type = "text" name = "username"> </TD>
<TD width = 101 Height = 25> <Div align = center> <input type = "image" src = "image/buy_yanzheng.jpg" name = "checkuser" id = "checkuser" onclick = "callserver (); return false; "> </div> </TD>
<TD width = 297 Height = 25> (verify whether your user name is occupied) </TD> </tr>
<Tr>
<TD Height = 25>
<Div align = right> * </div> </TD>
<TD Height = 25> password: </TD>
<TD colspan = 3 Height = 25> <input type = "password" name = "password"> & nbsp; (set a password of more than 6 characters) </TD> </tr>
<Tr>
<TD Height = 25>
<Div align = right> * </div> </TD>
<TD Height = 25> Confirm Password: </TD>
<TD colspan = 3 Height = 25> <input type = "password" name = "repassword"> & nbsp; (enter the password again) </TD> </tr>
<Tr>
<TD Height = 25>
<Div align = right> * </div> </TD>
<TD Height = 25> User name: </TD>
<TD colspan = 3 Height = 25> <input type = "text" name = "zsname"> & nbsp; (Please leave your real name so that we can contact you, delivery for you !) </TD> </tr>
<Tr>
<TD Height = 25>
<Div align = right> * </div> </TD>
<TD Height = 25> sex: </TD>
<TD colspan = 3 Height = 25> <select class = buy_box name = usersex>
<Option selected> </option> <option value = male> male </option>
<Option value = female> female </option> </SELECT> </TD> </tr>
<Tr style = "line-Height: 30px">
<TD Height = 25>
<Div align = right> * </div> </TD>
<TD Height = 25> contact number: </TD>
<TD colspan = 3 Height = 25> <input type = "text" name = "telephone"> (enter the area code and phone number) </TD>
</Tr>
<Tr>
<TD Height = 25>
<Div align = right> * </div> </TD>
<TD Height = 25> Email: </TD>
<TD colspan = 3 Height = 25> <input type = "text" name = "email"> (enter an email address) </TD> </tr>
<Tr>
<TD Height = 25>
<Div align = right> * </div> </TD>
<TD Height = 25> Mailing address: </TD>
<TD colspan = 3 Height = 25> <textarea name = "Address" rows = 3 Cols = 60> </textarea> </BR> (enter the correct mailing address, in order to accurately and timely deliver the goods you ordered) </TD> </tr>
<Tr>
<TD Height = 25>
<Div align = right> * </div> </TD>
<TD Height = 25> zip code: </TD>
<TD colspan = 3 Height = 25> <input type = "text" name = "zipcode" size = "2" maxlength = "6"> (Please enter a 6-digit ZIP code) </TD> </tr>
<Tr>
<TD Height = 25> <Div align = right> * </div> </TD>
<TD Height = 25> credit card number: </TD>
<TD colspan = 3 Height = 25> <input type = "text" name = "idcard">
(Enter a 16-digit credit card number) </TD>
</Tr>
<Tr>
<TD Height = 25> & nbsp; </TD>
<TD Height = 25> & nbsp; </TD>
<TD colspan = 3 Height = 25> & nbsp; </TD> </tr>
<Tr>
<TD colspan = 2> </TD> </tr>
<Tr>
<TD Height = 46> & nbsp; </TD>
<TD colspan = 4> <br> </TD>
</Tr>
<Tr>
<TD Height = 46>
</TD>
<TD colspan = 4>
<HR Align = left width = 600 size = 1>

<Div align = center>
<Input type = "Submit" name = "Submit" value = "register" onclick = "checkuserreg ('add'); Return false;"/>
<Input type = "reset" name = "reset" value = "Refill">
<Input name = "action" type = "hidden" value = ""/>
</Div> </TD> </tr>
</Table> </form>

Ajax is sent to the processing and response page:

<% @ Page Language = "Java" Import = "Java. util. *" pageencoding = "UTF-8" %>
<% @ Page import = "com. Bay. Bean. *" %>
<%
String username = request. getparameter ("username ");
User user = new user ();
User. setusercode (username );
If (user. ischeckreg ())
{Out. Write ("congratulations, this user can register and use ");
} Else {out. Write ("sorry, this user name already exists, re-enter ");}
%>