Many systems now register, log in or publish information modules are added to the random code function, is to avoid automatic registration program or the use of automatic publishing programs.
The verification code is actually randomly select some characters to display in the form of a picture on the page, if you want to submit the operation of the same time you need to submit the characters on the picture at the same time, if the submitted characters and server session Save the difference, the submission information is considered invalid. In order to avoid automated program analysis and resolution of pictures, usually randomly generated in the picture some interference lines or distorted characters to increase the difficulty.
we can use the servlet to implement the random authentication code.
Copy Code code as follows:
Package com.servlet;
Import Java.awt.Color;
Import Java.awt.Font;
Import Java.awt.Graphics2D;
Import Java.awt.image.BufferedImage;
Import Java.util.Random;
Import Javax.imageio.ImageIO;
Import javax.servlet.ServletException;
Import Javax.servlet.ServletOutputStream;
Import Javax.servlet.http.HttpServlet;
Import Javax.servlet.http.HttpServletRequest;
Import Javax.servlet.http.HttpServletResponse;
Import javax.servlet.http.HttpSession;
/**
* Generate random verification code
* @author Bitiliu
*
*/
public class Validatecodeservlet extends HttpServlet
{
Private static final long serialversionuid = 1L;
The width of the verification code picture.
private int width=60;
The height of the verification code picture.
private int height=20;
Number of verification code characters
private int codecount=4;
private int x=0;
Font height
private int fontheight;
private int Codey;
Char[] codesequence = {' 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 ', ' 0 ', ' 1 ', ' 2 ', ' 3 ', ' 4 ', ' 5 ', ' 6 ', ' 7 ', ' 8 ', ' 9 '};
/**
* Initialize validation picture properties
*/
public void Init () throws Servletexception
{
Get the initial information from the Web.xml
Width
String strwidth=this.getinitparameter ("width");
Height
String strheight=this.getinitparameter ("height");
Number of characters
String strcodecount=this.getinitparameter ("Codecount");
Converts the configured information to a numeric value
Try
{
if (Strwidth!=null && strwidth.length ()! =0)
{
Width=integer.parseint (Strwidth);
}
if (Strheight!=null && strheight.length ()! =0)
{
Height=integer.parseint (Strheight);
}
if (Strcodecount!=null && strcodecount.length ()! =0)
{
Codecount=integer.parseint (Strcodecount);
}
}
catch (NumberFormatException e)
{}
x=width/(codecount+1);
Fontheight=height-2;
codey=height-4;
}
protected void Service (HttpServletRequest req, HttpServletResponse resp)
Throws Servletexception, Java.io.IOException {
Define Image Buffer
BufferedImage buffimg = new BufferedImage (
width, height,bufferedimage.type_int_rgb);
Graphics2D g = buffimg.creategraphics ();
Create a random number generator class
Random Random = new Random ();
To fill an image with white
G.setcolor (Color.White);
G.fillrect (0, 0, width, height);
To create a font, the size of the font should be based on the height of the picture.
Font font = new Font ("Fixedsys", Font.plain, Fontheight);
Sets the font.
G.setfont (font);
Draw a border.
G.setcolor (Color.Black);
G.drawrect (0, 0, width-1, height-1);
Randomly generated 160 lines of interference, so that the image of the authentication code is not easily detected by other programs.
G.setcolor (Color.Black);
for (int i = 0; I < 160; 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);
}
Randomcode is used to save randomly generated CAPTCHA code so that the user can authenticate after logging in.
StringBuffer Randomcode = new StringBuffer ();
int red = 0, green = 0, blue = 0;
A validation code that randomly generates CODECOUNT numbers.
for (int i = 0; i < Codecount; i++) {
The number of validated codes generated randomly.
String Strrand = string.valueof (Codesequence[random.nextint (36)]);
Produces a random color component to construct a color value, so that the color values of each digit of the output will be different.
Red = random.nextint (255);
Green = Random.nextint (255);
Blue = Random.nextint (255);
Draws the validation code into the image with a randomly generated color.
G.setcolor (New Color (red, green, blue));
g.DrawString (Strrand, (i + 1) * x, Codey);
The resulting four random numbers are grouped together.
Randomcode.append (Strrand);
}
Saves a four-bit number of Authenticode to the session.
HttpSession session = Req.getsession ();
Session.setattribute ("Validatecode", randomcode.tostring ());
Disables image caching.
Resp.setheader ("Pragma", "No-cache");
Resp.setheader ("Cache-control", "No-cache");
Resp.setdateheader ("Expires", 0);
Resp.setcontenttype ("Image/jpeg");
Outputs the image to the servlet output stream.
Servletoutputstream SOS = Resp.getoutputstream ();
Imageio.write (buffimg, "JPEG", SOS);
Sos.close ();
}
}
need to declare servlet in Web.xml
Copy Code code as follows:
<servlet>
<servlet-name>ValidateCodeServlet</servlet-name>
<servlet-class>com.servlet.ValidateCodeServlet</servlet-class>
<init-param>
<param-name>width</param-name>
<param-value>200</param-value>
</init-param>
<init-param>
<param-name>height</param-name>
<param-value>80</param-value>
</init-param>
<init-param>
<param-name>codeCount</param-name>
<param-value>5</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>ValidateCodeServlet</servlet-name>
<url-pattern>/validateCodeServlet</url-pattern>
</servlet-mapping>
