JSP instance: Java implementation Random authentication code function Example

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 of automatic recognition.

Here, we use the servlet to implement the random authentication code.

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; /** * Generates a random verification code * @author Bitiliu * * */public class Validatecodeservlet extends HttpServlet {private static final lo
 
 ng 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 authentication 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 Verify picture properties/public void init () throws Servletexception {//Get initial information/width String s from web.xml
  Trwidth=this.getinitparameter ("width");
  Height String strheight=this.getinitparameter ("height"); 
  
  Number of characters String strcodecount=this.getinitparameter ("Codecount");
   Converts the configured information to a numeric 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);
  The catch (NumberFormatException e) {} x=width/(codecount+1);
  Fontheight=height-2;
  
 codey=height-4; } protected void Service (HttpServletRequest req, HttpServletResponse resp) throws Servletexception, Java.io.IO Exception {//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 ();
  Fill the image with a 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 a randomly generated authentication 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++) {//Get a randomly generated captcha number.
   String Strrand = string.valueof (Codesequence[random.nextint (36)]); Produces a random color component to construct a color value so that the outputThe color values for each digit are 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);
  ///Save the four-digit CAPTCHA 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

<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>

Pages that need to be referenced can be written like this:

<ccid_file values= "Validatecodeservlet" width= "100/"/>

After a user submits, the authentication code entered by the user can be compared to the string saved in the session to achieve the validation effect.