The method of Jsp+servlet programming to implement verification code _jsp programming

The example of this article describes the method of Jsp+servlet programming to implement the verification code. Share to everyone for your reference, specific as follows:

Here are two classes, one for the authentication code implementation, and one for the background servlet to verify that the input is correct:

Codeutil.java--------Verification Code is specifically implemented:

Package util; 
Import Java.awt.Color; 
Import Java.awt.Font; 
Import Java.awt.Graphics; 
Import Java.awt.image.BufferedImage; 
Import java.io.IOException; 
Import Java.io.OutputStream; 
Import Java.io.PrintWriter; 
Import Java.util.Random; 
Import Javax.imageio.ImageIO; 
Import javax.servlet.ServletException; 
Import Javax.servlet.http.HttpServlet; 
Import Javax.servlet.http.HttpServletRequest; 
Import Javax.servlet.http.HttpServletResponse; 
Import javax.servlet.http.HttpSession; 
Import Javax.servlet.jsp.PageContext; 
Import javax.servlet.jsp.tagext.BodyContent; 
Import Com.sun.image.codec.jpeg.JPEGCodec; 
Import Com.sun.image.codec.jpeg.JPEGImageDecoder; 
Import Com.sun.image.codec.jpeg.JPEGImageEncoder; public class Codeutil extends HttpServlet {public void service (HttpServletRequest request, httpservletresponse response 
  ) throws Servletexception, IOException {//system.out.println ("hahaha"); 
  Response.setcontenttype ("Image/jpeg"); Set page does not cache Response.setheader ("PragMa "," No-cache ");  
  Response.setheader ("Cache-control", "No-cache"); 
  Response.setdateheader ("Expires", 0); 
  Create an image in memory int width = 90; 
  int height = 35; 
  BufferedImage image = new BufferedImage (WIDTH,HEIGHT,BUFFEREDIMAGE.TYPE_INT_RGB); 
  Gets the graphics context Graphics g = image.getgraphics (); 
  Random class Random Random = new Random (); 
  Set Background G.setcolor (Getrandcolor (200, 250)); 
  G.fillrect (0, 0, width, height); 
  Set font g.setfont (new Font ("Times New Roman", font.plain,30);  
  Randomly generated disturbing line G.setcolor (Getrandcolor (160, 200));  
   for (int i = 0; i < 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); ///Randomly generate 4-bit captcha string[] codes = {"0", "1", "2", "3", "4", "5", "" 6 "," 7 "," 8 "," 9 "," 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", "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 "}; 
  String code = ""; 
   for (int i=0;i<4;i++) {String str = codes[random.nextint (codes.length)]; 
   Code + + str; 
   Display the authentication code to the image G.setcolor (new Color (+ Random.nextint (), + random.nextint (110)); Call functions come out of the same color, probably because the seeds are too close, so only directly generated g.drawstring (str, * i +13, 27); 
  Text spacing *i+ distance from left margin, top margin} HttpSession session=request.getsession (); 
  The authentication code is stored in the session session.setattribute ("code", code);  
  Image entry into force g.dispose (); 
  Output image to page imageio.write (image, "JPEG", Response.getoutputstream ()); Add the following code, the runtime will not appear Java.lang.IllegalStateException:getOutputStream () has already been called ... 
  such as abnormal response.getoutputstream (). Flush (); 
  Response.getoutputstream (). Close (); 
 Response.flushbuffer (); 
  //Get random color private 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); 

 } 
}

Checkcodeutil.java-----------User Input validation

Package util; 
Import java.io.IOException; 
Import Java.io.PrintWriter; 
Import javax.servlet.ServletException; 
Import Javax.servlet.http.HttpServlet; 
Import Javax.servlet.http.HttpServletRequest; 
Import Javax.servlet.http.HttpServletResponse; 
Import javax.servlet.http.HttpSession; public class Checkcodeutil extends HttpServlet {public void service (HttpServletRequest request, HttpServletResponse Res 
  Ponse) throws Servletexception, IOException {request.setcharacterencoding ("utf-8"); 
  Response.setcontenttype ("Text/html;charset=utf-8"); 
  PrintWriter out = Response.getwriter (); 
  Obtain the verification code from session HttpSession session=request.getsession (); 
  String Code=session.getattribute ("code"). toString (); 
  SYSTEM.OUT.PRINTLN (code); 
  Gets the user input verification code String input=request.getparameter ("code"); 
  SYSTEM.OUT.PRINTLN (input); 
   if (code.equalsignorecase (input)) {//Forwarding data Request.setattribute ("Result", "true"); Request.getrequestdispatcher ("test/regist.jsp"). Forward (Request, response); 
  Response.sendredirect (Request.getcontextpath () + "/regist/regist.jsp"); 
   }else{Request.setattribute ("Result", "false"); 
  Request.getrequestdispatcher ("test/regist.jsp"). Forward (request, response); 

 } 
 } 
}

To test the page effect:

To test the page code:

<%@ page session= "true" pageencoding= "Utf-8 contenttype=" text/html; Charset=utf-8 "%> <! DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en" "Http://www.w3.org/TR/html4/loose.dtd" >  

I hope this article will help you with JSP programming.