java 后台实现一验证码功能传递前台

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验证码的4种效果：

第一种：数字和英文的组成

第二种:全英文

第三种：全数字

第四种：计算

首先创建一个LoginVerification.java的类，

  public class LoginVerification  extends HttpServlet {   Random random = new Random(); //设置验证码的文本 String sRand="";        int width=200, height=40;      BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);     Graphics g;      private static final String CONTENT_TYPE = "text/html; charset=utf-8";         public void init() throws ServletException         {             super.init();         }        //设置随机的背景颜色    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);         }         public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException         {             response.setHeader("Pragma","No-cache");             response.setHeader("Cache-Control","no-cache");             response.setDateHeader("Expires", 0);             //设置类型        response.setContentType("image/jpeg");             //设置字体的大小           Font mFont = new Font("Times New Roman",Font.PLAIN,28);                       g = image.getGraphics();        g.setColor(getRandColor(200,250));             g.fillRect(0, 0, width, height);             g.setColor(new Color(102,102,102));             g.drawRect(0, 0, width-1, height-1);             g.setFont(mFont);                 //设置颜色        g.setColor(getRandColor(160,200));            for (int i=0;i<155;i++)             {                 int x = random.nextInt(width - 1);                 int y = random.nextInt(height - 1);                 int xl = random.nextInt(6) + 1;                 int yl = random.nextInt(12) + 1;                 g.drawLine(x,y,x + xl,y + yl);             }             for (int i = 0;i < 70;i++)             {                 int x = random.nextInt(width - 1);                 int y = random.nextInt(height - 1);                 int xl = random.nextInt(12) + 1;                 int yl = random.nextInt(6) + 1;                 g.drawLine(x,y,x - xl,y - yl);             }            //设置验证码的类型        four();        HttpSession session = request.getSession(true);          //设置session使其进行效验        session.setAttribute("validate",sRand);             g.dispose();             ImageIO.write(image, "JPEG", response.getOutputStream());         }        // 英文字符加数字的验证码      public void one(){         String[] letter = { "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" };           for (int i = 0; i < 4; i++) {               String tempRand = "";               if (random.nextBoolean()) {                   tempRand = String.valueOf(random.nextInt(10));               } else {                   tempRand = letter[random.nextInt(25)];                  /* if (random.nextBoolean()) {// 随机将该字母变成小写                       tempRand = tempRand.toLowerCase();                   }  */             }               sRand += tempRand;               g.setColor(new Color(20 + random.nextInt(10), 20 + random                       .nextInt(110), 20 + random.nextInt(110)));               g.drawString(tempRand,20 * i + 20, 30);           }      }        //英文    public void two(){    for (int i=0;i<5;i++)             {                 int itmp = random.nextInt(26) + 65;                 char ctmp = (char)itmp;                 sRand += String.valueOf(ctmp);                 g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));             g.drawString(String.valueOf(ctmp),20*i+10,30);             }        }    //4个数    public void three(){     for (int i = 0; i < 4; i++) {               String rand = String.valueOf(random.nextInt(10));               sRand += rand;               // 将认证码显示到图象中               g.setColor(new Color(20 + random.nextInt(110), 20 + random                       .nextInt(110), 20 + random.nextInt(110)));               // 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成              g.drawString(rand,20*i+10,30);           }     }    //中文 肆+？=24    public void four(){   String[] cn = { "壹", "贰", "叁", "肆", "伍", "陆", "柒", "捌", "玖", "拾" };          int x = random.nextInt(10) + 1;          int y = random.nextInt(30);          sRand = String.valueOf(y);        g.setFont(new Font("楷体", Font.PLAIN, 25));// 设定字体          g.setColor(new Color(20 + random.nextInt(10), 20 + random.nextInt(110),                  20 + random.nextInt(110)));          g.drawString(cn[x - 1], 1 * 1 + 6, 30);          g.drawString("+", 33, 30);          g.drawString("？", 50, 30);          g.drawString("=", 62, 30);          g.drawString(String.valueOf(x + y), 75, 30);    }}

在前台写入图片：

 <img id="codevalidate" src="login/AuthImageServlet" width="200" height="30" style="margin-left: 10px" onclick="changeUrl()">      function changeUrl() { var imgNode = document.getElementById("codevalidate");                    imgNode.src = "login/AuthImageServlet?t=" + Math.random();  // 防止浏览器缓存的问题         }

其次在web.xml文件中添加以下片段

<servlet>    <servlet-name>AuthImageServlet</servlet-name>    <servlet-class>com.jyft.common.LoginVerification</servlet-class>    <load-on-startup>1</load-on-startup>  </servlet>  <servlet-mapping>    <servlet-name>AuthImageServlet</servlet-name>    <url-pattern>/login/AuthImageServlet</url-pattern>  </servlet-mapping>

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