Code accumulation-Generate CAPTCHA servlet

 Packageweb;ImportJava.awt.Color;ImportJava.awt.Font;ImportJava.awt.Graphics2D;ImportJava.awt.image.BufferedImage;Importjava.io.IOException;ImportJava.util.Random;ImportJavax.imageio.ImageIO;Importjavax.servlet.ServletException;ImportJavax.servlet.ServletOutputStream;ImportJavax.servlet.http.HttpServlet;Importjavax.servlet.http.HttpServletRequest;ImportJavax.servlet.http.HttpServletResponse;Importjavax.servlet.http.HttpSession; Public classCheckcodeextendsHttpServlet {Private Static Final LongSerialversionuid = -5051097528828603895l; /*** The name of the verification code session. */    Private Static FinalString session_att_name = "Validatecode"; /*** Verify the width of the code picture. */    Private intwidth = 100; /*** Verify the height of the code picture. */    Private intHeight = 30; /*** Number of verification code characters*/    Private intCodecount = 4; /*** Font height*/    Private intFontheight; /*** The x-axis value of the first character, because the subsequent character coordinates increment sequentially, so their x-axis value is a multiple of Codex*/    Private intCodeX; /*** Codey, verify the y-axis value of the character, because parallel so the value is the same*/    Private intCodey; /*** Codesequence Indicates the sequence value that the character is allowed to appear*/    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 voidInit ()throwsservletexception {//getting initial information from Web. XML//widthString Strwidth = This. Getinitparameter ("width"); //HeightString strheight = This. Getinitparameter ("height"); //Number of charactersString Strcodecount = This. Getinitparameter ("Codecount"); //convert 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) {e.printstacktrace (); }        //width-4 Remove the left and right positions, so that the verification code more concentrated display, reduce the more concentrated. //codecount+1//equal to the width of the display, including the left and right sides of the spaceCodeX = (width-4)/(codecount+1); //height-10 Centralized display verification codeFontheight = height-10; Codey= Height-7; }     Public voidService (HttpServletRequest request, httpservletresponse response)throwsservletexception, IOException {//defining the image bufferBufferedImage buffimg =Newbufferedimage (width, height, bufferedimage.type_int_rgb); Graphics2D GD=Buffimg.creategraphics (); //Create a random number generator classRandom random =NewRandom (); //fill the image with whiteGd.setcolor (Color.light_gray); Gd.fillrect (0, 0, width, height); //To create a font, the size of the font should depend on the height of the image. Font font =NewFont ("Fixedsys", Font.plain, fontheight); //sets the font. Gd.setfont (font); //draw a border. Gd.setcolor (Color.Black); Gd.drawrect (0, 0, width-1, height-1); //randomly generates 160 lines of interference so that the authentication code in the image is not easily detected by other programs. Gd.setcolor (Color.gray);  for(inti = 0; I < 16; i++) {            intx =random.nextint (width); inty =random.nextint (height); intXL = Random.nextint (12); intYL = Random.nextint (12); Gd.drawline (x, y, x+ XL, Y +yl); }        //The Randomcode is used to save randomly generated verification codes so that users can log in and authenticate. StringBuffer Randomcode =NewStringBuffer (); intRed = 0, green = 0, blue = 0; //random generation of Codecount number verification code.          for(inti = 0; i < Codecount; i++) {            //get a randomly generated captcha number. String Strrand = string.valueof (Codesequence[random.nextint (36)]); //generates a random color component to construct a color value so that the output will have a different color value for each digit. Red = Random.nextint (255); Green= Random.nextint (255); Blue= Random.nextint (255); //draws the verification code into the image with a randomly generated color. Gd.setcolor (NewColor (Red,green,blue)); Gd.drawstring (Strrand, (i+ 1) *CodeX, Codey); //The resulting four random numbers are grouped together. randomcode.append (Strrand); }        //Save the four-digit verification code to the session. HttpSession session =request.getsession ();        Session.setattribute (Session_att_name, randomcode.tostring ()); //suppresses image caching. Response.setheader ("Pragma", "No-cache"); Response.setheader ("Cache-control", "No-cache"); Response.setdateheader ("Expires", 0); Response.setcontenttype ("Image/jpeg"); //output the image to the servlet output stream. Servletoutputstream SOS =Response.getoutputstream (); Imageio.write (buffimg,"JPEG", SOS);    Sos.close (); }          Public StaticString Getvalidatecode (httpservletrequest request) {HttpSession session=request.getsession (); Object obj=Session.getattribute (session_att_name); if(obj!=NULL){                returnobj.tostring (); }            return""; }         Public Static voidRemovevalidatecode (HttpServletRequest request) {HttpSession session=request.getsession ();        Session.removeattribute (Session_att_name); }}

Code accumulation-Generate CAPTCHA servlet