Session instance: one-time verification code

 

The cookie function is not disabled.

URL rewriting

When a request is submitted for the first time, when the request message does not contain the cookie of the session, the URL rewriting technology is used to generate a response.

When you submit a request later, the request message will contain the session cookie.

The cookie function is not disabled: All response messages generated are rewritten using URLs.

 

Session instance: one-time verification code

Loginform.html

Checkcodeservlet: generate a verification code in the Session Object

Loginformservlet: Check whether the entered verification code is consistent with the verification code displayed in the image.

Implementation Code:

Checkcodeservlet

Private Static final long serialversionuid = 1l;

Private Static int width = 60;

Private Static int Height = 20; // The image height is 20 pixels.

Doget Method

Response. setcontenttype ("image/JPEG"); // type of the response content

 

Servletoutputstream out = response. getoutputstream ();

 

Httpsession session = request. getsession (); // obtain the session object

 

// The Verification Code image cannot be cached on the client

Response. setheader ("Pragma", "No-Cache ");

Response. setheader ("cache-controll", "No-Cache ");

Response. setintheader ("expires", 0); // set the expiration time

 

// Drawing -- opening a buffer in the memory ---- background

Bufferedimage Bi = new bufferedimage (width, height,

Bufferedimage. type_int_rgb); // specifies the width and height of the image.

Graphics G = Bi. getgraphics (); // obtain the paint brush by calling the method of drawing paper.

 

Drawbackground (g );

 

// Generate a random Verification Code

Char [] rands = generatecheckcode (); // a four-digit verification code is randomly generated.

 

// Output, painted on paper

Drawrands (G, rands );

 

Bytearrayoutputstream Bos = new bytearrayoutputstream ();

ImageIO. Write (Bi, "Jpeg", Bos); // format of jepg Conversion

// Define a byte array

Byte [] Buf = Bos. tobytearray (); // converts the content in the Bi object to a byte array

Out. Write (BUF );

 

// Set the length of the response content

Response. setcontentlength (BUF. Length );

 

Session. setattribute ("checkcode", new string (rands ));

 

Out. Flush ();

Out. Close ();

}

Drawrands Method

Private void drawrands (Graphics g, char [] rands ){

// Paint brush color

G. setcolor (color. Black );

// Font of the output character, which is bold and skewed. The font size is 18.

G. setfont (new font (null, Font. italic | font. Bold, 18 ));

// Output characters

G. drawstring ("" + rands [0], 1, 15); // contains 1st characters

G. drawstring ("" + rands [1], 16, 14); // contains 2nd characters

G. drawstring ("" + rands [2], 31, 18); // contains 3rd characters

G. drawstring ("" + rands [3], 46, 12); // contains 4th characters

System. Out. println ("================ ");

System. Out. println (new string (rands ));

}

Generatecheckcode Method

Private char [] generatecheckcode (){

String chars = "0123456789 abcdefghijklmnopqrstuvwxyz"; // put all possible characters in an array

// Define an array for storing random numbers

Char rands [] = new char [4];

For (INT I = 0; I <4; I ++ ){

Int random = (INT) (math. Random () * 36); // randomly generates subscript in Chars

Rands [I] = chars. charat (random );

}

Return rands;

}

Drawbackground Method

Private void drawbackground (Graphics g ){

// Draw the background

G. setcolor (new color (0 xdcdcdc ));

G. fillrect (0, 0, width, height); // filled rectangle, top left corner and bottom right corner vertex coordinates

 

// Draw interference lines

For (INT I = 0; I <120; I ++ ){

// Randomly generate data, coordinates in the upper left corner

Int x = (INT) (math. Random () * width );

Int y = (INT) (math. Random () * Height );

 

// The elliptical color is random.

Int Red = (INT) (math. Random () * 255 );

Int Green = (INT) (math. Random () * 255 );

Int Blue = (INT) (math. Random () * 255 );

G. setcolor (new color (red, green, blue ));

 

G. drawoval (X, Y, 1, 0); // randomly generates elliptical lines, not filled

}

}

Loginformservlet

Httpsession session = request. getsession ();

String code = request. getparameter ("checkcode ");

String value = session. getattribute ("checkcode"). tostring ();

If(Value. Equals (CODE )){

Out. println ("correct Verification Code ");

}Else{

Out. println ("<font color = Red> Incorrect verification code </font> ");

}

Loginform.html

<H3> logon page with verification code

<Form method ="Post"Action ="Loginformservlet"Name ="Form1">

Username: <input type ="Text"Name ="Username"/></BR>

Password & nbsp; Code: <input type ="Password"Name ="Password"/></BR>

Verification Code: <input type ="Text"Name ="Checkcode"/>

<IMG src ="Servlet/checkcode"/></BR>

<Input type ="Submit"Value ="Submit"/>

</Form>