Image Verification Code overview and implementation steps, verification code overview steps

Image Verification Code overview and implementation steps, verification code overview steps

I. Image Verification Code Overview:
Many websites have this implementation.

Purpose:
To improve system security
With the verification code, we can ask the user to enter the user name, password, and other information, at the same time enter the text on the image, the user submits

The system will first extract the generated verification code from the session and compare it with the verification code entered by the user.

Equivalent, indicating that the user logs on from the logon interface. Otherwise, the user is invalid.


The verification code is used to ensure that the system can be used only after successful logon, so that users can directly access the address bar.

Enter the page to access

That is to say, to use the verification code, the user must first log on to


Ii. Verification Implementation Method
Two key classes are used, which are related to the output of images.


BufferedImage im = new BufferedImage (60, 20, BufferedImage. TYPE_INT_RGB );
// The first parameter im represents an image object
// JPG indicates the image output type
// Response. getOutputStream () represents the output stream of a response, that is, you access this servlet.

Servlet will show you an image
ImageIO. write (im, "JPG", response. getOutputStream ());



3. Implementation steps
1. Use BufferedImage to generate an image, then use ImageIO output, and specify it as JPG
BufferedImage im = new BufferedImage (60, 20, BufferedImage. TYPE_INT_RGB );
// The first parameter im represents an image object
// JPG indicates the image output type
// Response. getOutputStream () represents the output stream of a response, that is, you access this servlet.

Servlet will show you an image
ImageIO. write (im, "JPG", response. getOutputStream ());



2. Get the image Drawing Object
Graphics g = im. getGraphics ();

3. Fill in the drawing Area
Random rm = new Random ();
Color c = new Color (rm. nextInt (255), rm. nextInt (255), rm. nextInt (255 ));
G. setColor (c );
// Fill in the color of the entire image
G. fillRect (0, 0, 60, 20 );



4. Output numbers to the image
G. setColor (new Color (rm. nextInt (255), rm. nextInt (255), rm. nextInt (255 )));
G. setFont (new Font (" 文 ", Font. BOLD | Font. ITALIC, 28 ));
G. drawString ("8", 1, 18 );

5. Random 4-digit number

// Four digits are randomly generated.
For (int I = 0; I <4; I ++ ){
G. setColor (new Color (rm. nextInt (255), rm. nextInt (255), rm. nextInt (255 )));
G. setFont (new Font ("Gungsuh", Font. BOLD | Font. ITALIC, 22 ));
G. drawString ("" + rm. nextInt (10), (I * 15) + 2, 18 );
}


6. randomly generate Chinese Characters
String str = "the chest is thunderous and faces such as Pinghu can worship the generals ";
For (int I = 0; I <4; I ++ ){
G. setColor (new Color (rm. nextInt (255), rm. nextInt (255), rm. nextInt (255 )));
G. setFont (new Font ("Gungsuh", Font. BOLD | Font. ITALIC, 15 ));
G. drawString ("" + str. charAt (rm. nextInt (str. length (), (I * 15) + 2, 18 );
}


7. How to introduce the verification code on the page:


8. Save the number for Logon comparison
// Save the four digits to the session for comparison when the user logs on
Request. getSession (). setAttribute ("piccode", sbf. toString ());


9. logon Verification
First, verify that the user exists in the Database. If yes, verify that the entered verification code is consistent.
After the verification is successful, you need to forward it to the relevant operation page.

Code example:

Boolean B _exist = login. validate (username, passwd );
// If this user exists
If (B _exist ){
String pic = "" + request. getSession (). getAttribute ("piccode ");
// Compare the verification code
If (! Pic. equals ("") & pic. equals (code )){
// Store user information into the session for other purposes
Request. getSession (). setAttribute ("username", username );

Response. sendRedirect ("index. jsp ");
}
}
Iv. References:
Http://blog.163.com/jackie_howe/blog/static/199491347201272410322219/