Ajax verifies that the user name is registered

Ajax verifies that the user name is registered

var xmlHttp;
function Createxmlhttprequest () {//Create XMLHTTP Request object
if (window. ActiveXObject) {
Xmlhttp=new ActiveXObject ("Microsoft.XMLHTTP");
}else if (window. XMLHttpRequest) {
Xmlhttp=new XMLHttpRequest ();
}
}
Xmlhttp.onreadystatechange= Treatment Method
XmlHttp: This is the XMLHttpRequest object name
Processing method: This is a custom JavaScript method name
function Startrequest (userName) {//Send page request
Createxmlhttprequest ();
Xmlhttp.onreadystatechange=handlestatechange; Specify a method for handling server responses
Xmlhttp.open ("GET", "regsiterservlet?username=" +username,true);
Xmlhttp.send (NULL);
}
<script type= "Text/javascript" >
var xmlHttp;
function Createxmlhttprequest () {//Create XMLHTTP Request object
if (window. ActiveXObject) {
Xmlhttp=new ActiveXObject ("Microsoft.XMLHTTP");
}else if (window. XMLHttpRequest) {
Xmlhttp=new XMLHttpRequest ();
}
}
function Handlestatechange () {//Processing answer data
if (xmlhttp.readystate==4) {
if (xmlhttp.status==200) {
document.getElementById (' text '). Innerhtml=xmlhttp.responsetext;
}
}
}
function Startrequest (userName) {//Send page request
Createxmlhttprequest ();
Xmlhttp.onreadystatechange=handlestatechange;
Xmlhttp.open ("GET", "regsiterservlet?username=" +username,true);
Xmlhttp.send (NULL);
}
</script>
protected void ProcessRequest (HttpServletRequest request, httpservletresponse response)
Throws Servletexception, IOException {
Response.setcontenttype ("Text/html;charset=utf-8");
PrintWriter out = Response.getwriter (); Gets the character output stream of the reply object
try {
Userdao dao = new Userdao (); Create a Database action class
String userName = Request.getparameter ("UserName"); Gets the user name parameter of the request object
if (username==null| | Username.isempty ()) {
Back to prompt information
Out.print ("<font color= ' red ' > must enter user name </font>");
Return
}
Boolean hasuser = Dao.hasuser (userName); Determine if the database exists with the specified user name
if (hasuser) {//If there is a duplicate name
Return registered information
Out.print ("<font color= ' Red ' > The user name has been registered </font>");
} else {//otherwise
Prompt user to register
Out.print ("<font color= ' green ' > This user name can be used </font>");
}
} catch (Exception ex) {
Logger.getlogger (RegisterServlet.class.getName ()). log (Level.severe, NULL, ex);
} finally {
Out.close ();
}
}
public boolean hasuser (String userName) {
Boolean hasuser = false; Declares a check variable, false means no duplicate user
Connection conn = Getconn (); Connecting to a database
IF (conn! = null) {
Defining SQL query statements
String sql = "SELECT COUNT (*) from Tb_checkuser where username=?";
try {
PreparedStatement PS = conn.preparestatement (SQL);
Ps.setstring (1, userName); Set parameters for a query statement
ResultSet rs = Ps.executequery (); Execute SQL query
if (Rs.next ()) {
int count = Rs.getint (1); Get the number of users with the same name
if (Count > 0) {//If the number of users with the same name is greater than 0
Hasuser = true; Set check variable to true to represent user name
}
}
Rs.close (); Whether the resource
Ps.close ();
Conn.close ();
} catch (SQLException ex) {
Logger.getlogger (UserDao.class.getName ()). log (Level.severe, NULL, ex);
}
}
return hasuser;
}

Ajax verifies that the user name is registered