HTML registration verification code

Java code:

Public class captcharender implements serializable {

Private Static final long serialversionuid =-916701543933591834l;
Private Static final int width = 62, Height = 20;
Private Static final string [] strarr = {"3", "4", "5", "6", "7", "8", "9 ", "A", "B", "C", "D", "E", "F", "g", "H", "J", "K ", "M", "n", "P", "Q", "r", "S", "T", "U", "V", "W ", "X", "Y "};

Private string randomcodekey;

Public captcharender (string randomcodekey ){
If (stringkit. isblank (randomcodekey ))
Throw new illegalargumentexception ("randomcodekey can not be blank ");
This. randomcodekey = randomcodekey;
}

Public void render (){
Bufferedimage image = new bufferedimage (width, height, bufferedimage. type_int_rgb );
String vcode = drawgraphic (image );
Vcode = encrypt (vcode );
Cookie = new cookie (randomcodekey, vcode );
Cookie. setmaxage (-1 );
Cookie. setpath ("/");
Response. addcookie (cookie );
Response. setheader ("Pragma", "No-Cache ");
Response. setheader ("cache-control", "No-Cache ");
Response. setdateheader ("expires", 0 );
Response. setcontenttype ("image/JPEG ");

Servletoutputstream SOS = NULL;
Try {
SOS = response. getoutputstream ();
ImageIO. Write (image, "Jpeg", SOS );
} Catch (exception e ){
Throw new runtimeexception (E );
}
Finally {
If (SOS! = NULL)
Try {SOS. Close ();} catch (ioexception e) {e. printstacktrace ();}
}
}

Private string drawgraphic (bufferedimage image ){
// Obtain the image Context
Graphics G = image. creategraphics ();
// 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 ));

// 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 (strarr [random. nextint (strarr. Length)]);
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 of the called function is the same. It may be because the seed is too close and can only be directly generated.
G. drawstring (RAND, 13 * I + 6, 16 );
}

// The image takes effect
G. Dispose ();
Return srand;
}

/*
* Obtain random colors in a given range
*/
Private 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 );
}

Private Static final string encrypt (string srcstr ){
Try {
String result = "";
Messagedigest MD = messagedigest. getinstance ("MD5 ");
Byte [] bytes = md. Digest (srcstr. getbytes ("UTF-8 "));
For (byte B: bytes ){
String hex = integer. tohexstring (B & 0xff). touppercase ();
Result + = (Hex. Length () = 1 )? "0": "") + hex;
}
Return result;
} Catch (exception e ){
Throw new runtimeexception (E );
}
}

}

HTML code:

<Input type = "text" maxlength = "6" id = "random_code" name = "random_code" style = "width: 80px;">

<A href = "#" onclick = "changeimg ();"> <SPAN class = "login_style"> can't see it clearly? </Span> </a>

JS call:

Function changeimg ()
{
$ ("# Image"). ATTR ("src", '/IMG? S = '+ math. Random ());
}

Note:

There is a Temporary Folder temp in teomcat, and the verification code on the page is always X. Later, I checked the data room and couldn't find this because the temp temporary file was deleted.