JSP verification code page notes

First, I searched the code for JSP verification code generation on the Internet, as shown below:

Package com. servlet;

Import java. AWT. color;
Import java. AWT. Font;
Import java. AWT. graphics;
Import java. AWT. image. bufferedimage;
Import java. Io. ioexception;
Import java. Io. printwriter;
Import java. util. arrays;
Import java. util. collections;
Import java. util. List;
Import java. util. Random;

Import javax. ImageIO. ImageIO;
Import javax. servlet. servletexception;
Import javax. servlet. http. httpservlet;
Import javax. servlet. http. httpservletrequest;
Import javax. servlet. http. httpservletresponse;
Import javax. servlet. http. httpsession;

Public class validatecodeservlet extends httpservlet {

/**
*
*/
Private Static final long serialversionuid = 4008416931787800531l;

/**
* Constructor of the object.
*/
Public validatecodeservlet (){
Super ();
}

/**
* Destruction of the servlet. <br>
*/
Public void destroy (){
Super. Destroy (); // just puts "Destroy" string in log
}

/**
* The doget method of the servlet. <br>
*
* This method is called when a form has its tag Value Method equals to get.
*
* @ Param request
* The request send by the client to the server
* @ Param response
* The response send by the server to the client
* @ Throws servletexception
* If an error occurred
* @ Throws ioexception
* If an error occurred
*/
Public void doget (httpservletrequest request, httpservletresponse response)
Throws servletexception, ioexception {

// 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 painting object
Graphics G = image. getgraphics ();
// Set the background color
G. setcolor (getrandcolor (225,250 ));
G. fillrect (0, 0, width, height );
// Set the font
G. setfont (new font ("Times New Roman", Font. Bold, 20 ));

// Generates 155 random interference lines, making the authentication code in the image hard to be detected by other programs.
Random random = new random ();
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 = generateword ();
Byte [] cs = srand. getbytes ();
For (INT I = 0; I <4; I ++ ){
String A = new string (CS, I, 1 );
// String Rand = string. valueof (random. nextint (10 ));
String Rand =;
// 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, so it can only be generated directly.
G. drawstring (RAND, 13 * I + 6, 16 );
}

// Save the authentication code to the session
Httpsession session = request. getsession ();
Session. setattribute ("valicode", srand );

// The image takes effect
G. Dispose ();

// Output the image to the page
ImageIO. Write (image, "Jpeg", response. getoutputstream ());

}

/**
* The dopost method of the servlet. <br>
*
* This method is called when a form has its tag Value Method equals to post.
*
* @ Param request the request send by the client to the server
* @ Param response the response send by the server to the client
* @ Throws servletexception if an error occurred
* @ Throws ioexception if an error occurred
*/
Public void dopost (httpservletrequest request, httpservletresponse response)
Throws servletexception, ioexception {
Doget (request, response );
}

/**
* Obtain random colors in a given range
* @ Param FC
* @ Param BC
* @ Return
*/
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 string generateword (){
String [] beforeshuffle = new string [] {"1", "2", "3", "4", "5", "6", "7 ",
"8", "9", "A", "B", "C", "D", "E", "F", "g", "H ", "I", "J ",
"K", "L", "M", "n", "O", "P", "Q", "r", "S", "T ", "U", "V ",
"W", "X", "Y", "Z "};
List list = arrays. aslist (beforeshuffle );
Collections. Shuffle (list );
Stringbuilder sb = new stringbuilder ();
For (INT I = 0; I <list. Size (); I ++ ){
SB. append (list. Get (I ));
}
String aftershuffle = sb. tostring ();
String result = aftershuffle. substring (5, 9 );
Return result;
}
}

I processed it myself and used to generate random numbers. Here I use a list set.

Then reference this servlet on the JSP page, as shown below:

/validatecodeservlet" Flush = "true" onclick = "reloadimage ()" style = "vertical-align: bottom; cursor: Pointer "> </img>

Note: cursor: pointer is a hand-changing method, and reloadimage () is a js method.

Function reloadimage (){
Document. getelementbyid ('servletimg '). src = "<% = PATH %>/validatecodeservlet ";
}

Set the same address again.