Java Verification Code

Recently, a verification code is used in a J2EE system. The following is a good method to write the verification code as a servlet.

Import javax. servlet .*;
Import javax. servlet. http .*;
Import java. Io .*;
Import java. AWT .*;
Import java. AWT. image .*;
Import java. util .*;
Import javax. ImageIO .*;

/**
* @ Author yeeku. H. Lee kongyeeku@163.com
* @ Version 1.0
* <Br> copyright (C), 2005-2008, yeeku. H. Lee
* <Br> this program is protected by copyright laws.
* <Br> program name:
* <Br> date:
*/
Public class authimg extends httpservlet
{
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 ("image/JPEG ");

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 );
}
}
}
Here, the interference line is added and the verification code is saved using session,
On the login JSP page, Set
The Verification Code cannot be viewed clearly? <A href = "#" onclick = "Refresh ()"> click here to refresh </a>
Then write the refesh () function as follows:
<SCRIPT>
Function refresh ()
{
Document. getelementbyid ("authimg"). src = 'authimg? Now = '+ new date ();
}
</SCRIPT>
Adding now at the end prevents browser caching.

Finally, configure the servlet in Web. xml.

<Servlet>
<Servlet-Name> IMG </servlet-Name>
<Servlet-class> org. yeeku. Web. authimg </servlet-class>
</Servlet>

<Servlet-mapping>
<Servlet-Name> IMG </servlet-Name>
<URL-pattern>/authimg </url-pattern>
</Servlet-mapping>