Java Generate Verification Code

In order to prevent malicious users, or use the software to submit some content, you have to use a verification code to block, although this will affect the user experience, but in order to avoid some problems many sites have used a verification code; this afternoon reference to the document to get a verification code, here to share; This is a Web project, first of all, a page, Here is just a display verification code page index.jsp, using the default generated on it, the form did not commit, as follows

<%@ page language= "java" import= "java.util.*" pageencoding= "UTF-8"%><! DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en" >function  Refresh (obj) {        = " Imageservlet? " +math.random ();    }     </script>  
Here is the background code, here is a servlet, don't forget to configure the request URL in Web. xml
 PackageCom.wf.web;Importjava.io.IOException;Importjavax.servlet.ServletException;ImportJavax.servlet.http.HttpServlet;Importjavax.servlet.http.HttpServletRequest;ImportJavax.servlet.http.HttpServletResponse; Public classImageservletextendsHttpServlet {Private Static Final LongSerialversionuid = 1L;  Public voiddoget (httpservletrequest request, httpservletresponse response)throwsservletexception, IOException {response.setcontenttype ("Image/jpeg");//set the appropriate type to tell the browser what the output is for the pictureResponse.setheader ("Pragma", "No-cache");//Set the response header information to tell the browser not to cache this contentResponse.setheader ("Cache-control", "No-cache"); Response.setdateheader ("Expire", 0); Randomvalidatecode Randomvalidatecode=NewRandomvalidatecode (); Try{randomvalidatecode.getrandcode (request, response);//Output Image Method}Catch(Exception e) {e.printstacktrace (); }    }     Public voidDoPost (httpservletrequest request, httpservletresponse response)throwsservletexception, IOException {doget (request, response); }}
This class is a method of generating a verification code, as follows
 PackageCom.wf.web;ImportJava.awt.Color;ImportJava.awt.Font;ImportJava.awt.Graphics;ImportJava.awt.image.BufferedImage;ImportJava.util.Random;ImportJavax.imageio.ImageIO;Importjavax.servlet.http.HttpServletRequest;ImportJavax.servlet.http.HttpServletResponse;Importjavax.servlet.http.HttpSession; Public classRandomvalidatecode { Public Static FinalString Randomcodekey = "Randomvalidatecodekey";//The key that was placed in the session    PrivateRandom random =NewRandom (); PrivateString randstring = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";//randomly generated string        Private intwidth = 80;//Picture Width    Private intHeight = 26;//Picture High    Private intLinesize = 40;//number of interference lines    Private intStringnum = 4;//randomly generated number of characters    /** Get Fonts*/    PrivateFont GetFont () {return NewFont ("Fixedsys", font.center_baseline,18); }    /** Get Color*/    PrivateColor Getrandcolor (intFcintBC) {        if(FC > 255) FC= 255; if(BC > 255) BC= 255; intr = FC + Random.nextint (bc-fc-16); intg = FC + Random.nextint (bc-fc-14); intB = fc + Random.nextint (bc-fc-18); return NewColor (R,G,B); }    /*** Generate random images*/     Public voidGetrandcode (httpservletrequest request, httpservletresponse response) {HttpSession session=request.getsession (); //The BufferedImage class is an image class with a buffer, and the image class is the class used to describe the image informationBufferedImage image =NewBufferedImage (WIDTH,HEIGHT,BUFFEREDIMAGE.TYPE_INT_BGR); Graphics g= Image.getgraphics ();//The Graphics object that produces the image object, which can be used for various drawing operations on the imageG.fillrect (0, 0, width, height); G.setfont (NewFont ("Times New Roman", font.roman_baseline,18)); G.setcolor (Getrandcolor (110, 133)); //Draw Interference Lines         for(inti=0;i<=linesize;i++) {drowline (g); }        //Draw Random charactersString randomstring = "";  for(inti=1;i<=stringnum;i++) {RandomString=drowstring (g,randomstring,i);        } session.removeattribute (Randomcodekey);        Session.setattribute (Randomcodekey, randomstring);        System.out.println (RandomString);        G.dispose (); Try{imageio.write (image,"JPEG", Response.getoutputstream ());//output the In-memory picture to the client in a flowing form}Catch(Exception e) {e.printstacktrace (); }    }    /** Draw a string*/    PrivateString drowstring (Graphics g,string randomstring,inti)        {G.setfont (GetFont ()); G.setcolor (NewColor (Random.nextint (101), Random.nextint (111), Random.nextint (121))); String Rand=string.valueof (getrandomstring (Random.nextint (Randstring.length ())); RandomString+=Rand; G.translate (Random.nextint (3), Random.nextint (3)); g.DrawString (Rand,13*i, 16); returnRandomString; }    /** Draw Interference lines*/    Private voidDrowline (Graphics g) {intx =random.nextint (width); inty =random.nextint (height); intXL = Random.nextint (13); intYL = Random.nextint (15); G.drawline (x, y, x+XL, y+yl); }    /** get random characters*/     PublicString getrandomstring (intnum) {        returnstring.valueof (Randstring.charat (num)); }}
Web. xml file
<?XML version= "1.0" encoding= "UTF-8"?><Web-appversion= "2.5"xmlns= "Http://java.sun.com/xml/ns/javaee"Xmlns:xsi= "Http://www.w3.org/2001/XMLSchema-instance"xsi:schemalocation= "Http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">  <servlet>    <Servlet-name>Imageservlet</Servlet-name>    <Servlet-class>Com.wf.web.ImageServlet</Servlet-class>  </servlet>  <servlet-mapping>    <Servlet-name>Imageservlet</Servlet-name>    <Url-pattern>/imageservlet</Url-pattern>  </servlet-mapping>  <welcome-file-list>    <Welcome-file>index.jsp</Welcome-file>  </welcome-file-list></Web-app>
That's all, the verification code is stored in the session, or the cookie is OK, but must be clear in time
Java Generate Verification Code