A simple example of implementing JSP verification code _JSP programming

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<%@ page language= "java" pageencoding= "GBK"%>
<%@ page contenttype= image/jpeg "import=" java.awt.*,
java.awt.image.*,java.util.*,javax.imageio.*%>
<%!
Color getrandcolor (int fc,int BC) {///given range get random color
        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 Page not cached
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);

Get Graphics context
Graphics g = image.getgraphics ();

Generate Random Class
Random Random = new Random ();

Set Background color
G.setcolor (Getrandcolor (200,250));
G.fillrect (0, 0, width, height);

Set 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);

Randomly generated 155 lines of interference, so that the image of the authentication code is not easily 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);
}

Take a randomly generated authentication 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 in the image
G.setcolor (New Color (20+random.nextint), 20+random.nextint (a), 20+random.nextint (110));
The call function comes out with the same color, possibly because the seed is too close, so it can only be generated directly
g.DrawString (rand,13*i+6,16);
}

Save authentication Code in session
Session.setattribute ("Rand", SRand);

Image entry into force
G.dispose ();

Output image to Page
Imageio.write (Image, "JPEG", Response.getoutputstream ());
Out.clear ();

%>

Page reference:

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<TD width= "valign=" bottom "><div align=" left "></div></td>

Js:

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This.src= ' index/image.jsp? ' +math.random ();

Login time to obtain the code:

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String randb = (string) request.getsession (). getattribute ("Rand");