File that generates the verification code image ----- image. jsp
<% @ Page contenttype = "image/JPEG" Import = "Java. AWT. *, Java. AWT. image. *, Java. util. *, javax. imageIO. * "%>
<%!
Color getrandcolor (int fc, int BC) {// obtain a random color from a given range
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 );
}
%>
<%
// Set the page not to cache
Response. setheader ("Pragma", "No-Cache ");
Response. setheader ("cache-control", "No-Cache ");
Response. setdateheader ("expires", 0 );
// Create an image in memory
Int width = 60, Height = 20;
Bufferedimage image = new bufferedimage (width, height, bufferedimage. type_int_rgb );
// Obtain the image Context
Graphics G = image. getgraphics ();
// Generate a random class
Random random = new random ();
// Set the background color
G. setcolor (getrandcolor (200,250 ));
G. fillrect (0, 0, width, height );
// Set the font
G. setfont (new font ("Times New Roman", Font. Plain, 18 ));
// Draw a border
// G. setcolor (new color ());
// G. drawrect (0, 0, width-1, height-1 );
// Generates 155 random interference lines, making the authentication code in the image hard to be detected by other programs.
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 );
}
// Obtain the random ID code (4 digits)
String srand = "";
For (INT I = 0; I <4; I ++ ){
String Rand = string. valueof (random. nextint (10 ));
Srand + = rand;
// Display the authentication code to the image
G. setcolor (new color (20 + random. nextint (110), 20 + random. nextint (110), 20 + random. nextint (110); // The color from the call function is the same, probably because the seed is too close, so it can only be generated directly.
G. drawstring (RAND, 13 * I + 6, 16 );
}
// Save the authentication code to the session
Session. setattribute ("RAND", srand );
// The image takes effect
G. Dispose ();
// Output the image to the page
ImageIO. Write (image, "Jpeg", response. getoutputstream ());
%>
--------------- File --------- A. 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">
</Head>
<Body>
<Form method = post action = "check. jsp">
<Table>
<Tr>
<TD align = left> the verification code generated by the system: </TD>
<TD> </TD>
</Tr>
<Tr>
<TD align = left> enter the above verification code: </TD>
<TD> <input type = text name = Rand maxlength = 4 value = ""> </TD>
</Tr>
<Tr>
<TD colspan = 2 align = center> <input type = submit value = "Submit detection"> </TD>
</Tr>
</Form>
</Body>
</Html>
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