Step 1: Create a Servlet File
// Random Number
Public class generatecode extends httpservlet {
Private Static final long serialversionuid = 5039671097977591965l;
Protected void doget (httpservletrequest req, httpservletresponse resp)
Throws servletexception, ioexception {
Processrequest (req, resp );
}
Protected void dopost (httpservletrequest req, httpservletresponse resp)
Throws servletexception, ioexception {
Processrequest (req, resp );
}
Public void processrequest (httpservletrequest request,
Httpservletresponse response) throws ioexception {
Response. setcontenttype ("11.gif"); // set an image
Response. setheader ("Pragma", "No-Cache ");
Response. setheader ("cache-control", "No-Cache ");
Response. setdateheader ("expires", 0 );
Httpsession session = request. getsession ();
Int width = 80, Height = 20;
Bufferedimage image = new bufferedimage (width, height,
Bufferedimage. type_int_rgb );
Graphics G = image. getgraphics ();
Random random = new random ();
G. setcolor (getrandcolor (200,250 ));
G. fillrect (0, 0, width, height );
G. setfont (new font ("Times New Roman", Font. Plain, 18 ));
G. setcolor (getrandcolor (160,200 ));
For (INT I = 0; I <155; I ++ ){
Int x = random. nextint (width );
Int y = random. nextint (height );
Int XL = random. nextint (12 );
Int yl = random. nextint (12 );
G. drawline (X, Y, x + XL, Y + yl );
}
String srand = "";
For (INT I = 0; I <6; I ++ ){
String Rand = string. valueof (random. nextint (10 ));
Srand + = rand;
G. setcolor (new color (20 + random. nextint (110), 20 + random
. Nextint (110), 20 + random. nextint (110 )));
G. drawstring (RAND, 13 * I + 6, 16 );
}
Session. setattribute ("RAND", srand );
G. Dispose ();
Servletoutputstream responseoutputstream = response. getoutputstream ();
ImageIO. Write (image, "Jpeg", responseoutputstream );
Responseoutputstream. Flush ();
Responseoutputstream. Close ();
}
Color getrandcolor (int fc, int BC ){
Random random = new random ();
If (FC> 255)
Fc = 255;
If (BC> 255)
BC = 255;
Int r = FC + random. nextint (BC-Fc );
Int G = FC + random. nextint (BC-Fc );
Int B = FC + random. nextint (BC-Fc );
Return new color (R, G, B );
}
}
Step 2 set web. xml
<Servlet>
<Servlet-Name> showimgcode </servlet-Name>
<Servlet-class> generatecode </servlet-class>
</Servlet>
<Servlet-mapping>
<Servlet-Name> showimgcode </servlet-Name>
<URL-pattern>/11.gif</url-pattern>
</Servlet-mapping>
Step 3: Create the corresponding JSP
Index. jsp
<% @ Page contenttype = "text/html; charset = gb2312" %>
<! Doctype HTML public "-// W3C // dtd html 4.01 transitional // en">
<HTML>
<Head>
<Title> certificate code input page </title>
<Meta http-equiv = "Content-Type" content = "text/html; charset = gb2312">
<Meta HTTP-EQUIV = "Pragma" content = "no-Cache">
<Meta HTTP-EQUIV = "cache-control" content = "no-Cache">
<Meta HTTP-EQUIV = "expires" content = "0">
<Script language = "JavaScript">
Function myrefresh ()
{
Window. Location. Reload ();
}
</SCRIPT>
</Head>
<Body>
<Form method = post action = "check. jsp">
<Table>
<Tr>
<TD align = left>
The verification code generated by the system:
</TD>
<TD>
<Input type = "button" value = "cannot see clearly. Change" onclick = "myrefresh ()">
</TD>
</Tr>
<Tr>
<TD align = left>
Enter the above verification code:
</TD>
<TD>
<Input type = text name = Rand maxlength = 6 value = "">
</TD>
</Tr>
<Tr>
<TD colspan = 2 align = center>
<Input type = submit value = "Submit detection">
</TD>
</Tr>
</Table>
</Form>
</Body>
</Html>
Check. jsp
<% @ Page contenttype = "text/html; charset = gb2312" Language = "Java"
Errorpage = "" %>
<HTML>
<Head>
<Title> verification page </title>
<Meta http-equiv = "Content-Type" content = "text/html; charset = gb2312">
<Meta HTTP-EQUIV = "Pragma" content = "no-Cache">
<Meta HTTP-EQUIV = "cache-control" content = "no-Cache">
<Meta HTTP-EQUIV = "expires" content = "0">
</Head>
<Body>
<%
String Rand = (string) Session. getattribute ("RAND ");
String input = request. getparameter ("RAND ");
%>
The verification code generated by the system is:
<% = Rand %> <br>
The verification code you entered is:
<% = Input %> <br>
<Br>
<%
If (RAND. Equals (input )){
%>
<Font color = green> the input is the same and the authentication is successful! </Font>
<%
} Else {
%>
<Font color = red> If the input is different, authentication fails! </Font>
<%
}
%>
</Body>
</Html>
============================
Verification code for long-lived characters and Data
Public class CharactorCode extends HttpServlet {
Private static final long serialVersionUID = 4347521091342882490L;
Private Font mFont = new Font ("Arial Black", Font. PLAIN, 16 );
Public void init () throws ServletException {
Super. init ();
}
Color getRandColor (int fc, int bc ){
Random random = new Random ();
If (fc> 255)
Fc = 255;
If (bc> 255)
Bc = 255;
Int r = fc + random. nextInt (bc-fc );
Int g = fc + random. nextInt (bc-fc );
Int B = FC + random. nextint (BC-Fc );
Return new color (R, G, B );
}
Public void Service (httpservletrequest request, httpservletresponse response)
Throws servletexception, ioexception {
Response. setheader ("Pragma", "No-Cache ");
Response. setheader ("cache-control", "No-Cache ");
Response. setdateheader ("expires", 0 );
Response. setcontenttype ("11.gif ");
Int width = 100, Height = 18;
Bufferedimage image = new bufferedimage (width, height,
Bufferedimage. type_int_rgb );
Graphics G = image. getgraphics ();
Random random = new random ();
G. setcolor (getrandcolor (200,250 ));
G. fillrect (1, 1, width-1, height-1 );
G. setcolor (new color (102,102,102 ));
G. drawrect (0, 0, width-1, height-1 );
G. setfont (mfont );
G. setcolor (getrandcolor (160,200 ));
For (INT I = 0; I <155; I ++ ){
Int x = random. nextint (width-1 );
Int y = random. nextint (height-1 );
Int XL = random. nextint (6) + 1;
Int yl = random. nextint (12) + 1;
G. drawline (X, Y, x + XL, Y + yl );
}
For (INT I = 0; I <70; I ++ ){
Int x = random. nextint (width-1 );
Int y = random. nextint (height-1 );
Int XL = random. nextint (12) + 1;
Int yl = random. nextint (6) + 1;
G. drawline (X, Y, X-XL, Y-yl );
}
String srand = "";
For (INT I = 0; I <6; I ++ ){
String TMP = getrandomchar ();
Srand + = TMP;
G. setcolor (new color (20 + random. nextint (110), 20 + random
. Nextint (110), 20 + random. nextint (110 )));
G. drawstring (TMP, 15 * I + 10, 15 );
}
Httpsession session = request. getsession (true );
Session. setattribute ("RAND", srand );
G. Dispose ();
ImageIO. Write (image, "Jpeg", response. getoutputstream ());
}
Private string getrandomchar (){
Int Rand = (INT) math. Round (math. Random () * 2 );
Long itmp = 0;
Char CTMP = '/u0000 ';
Switch (RAND ){
Case 1:
Itmp = math. Round (math. Random () * 25 + 65 );
CTMP = (char) itmp;
Return string. valueof (CTMP );
Case 2:
Itmp = math. Round (math. Random () * 25 + 97 );
CTMP = (char) itmp;
Return string. valueof (CTMP );
Default:
Itmp = math. Round (math. Random () * 9 );
Return string. valueof (itmp );
}
}
}
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