jsp+servlet實現驗證碼

創建servlet

CodeServlet：
package com.lxs.servlet;
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.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;

public class CodeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String codes="abcdefghijklmnopqrstuvwxyzABCDEFJHIJKLMNOPQRSTUVWXYZ0123456789";
        BufferedImage img=new BufferedImage(80,30,BufferedImage.TYPE_3BYTE_BGR);
        Graphics g=img.getGraphics();
        //填充圖片
        g.setColor(new Color(255,255,255));
        g.fillRect(0, 0, 80, 30);
        //畫入五個隨機數
        Random rm=new Random();
        StringBuffer sb=new StringBuffer();
        for(int i=0;i<5;i++){
            int index=rm.nextInt(codes.length());
            char code=codes.charAt(index);
            g.setColor(new Color(rm.nextInt(256),rm.nextInt(256),rm.nextInt(256)));
            g.setFont(new Font("宋體", Font.BOLD, 25));
            g.drawString(code+"", 2+15*i, 22);
            sb.append(code);
        }

        //畫干擾線
        for(int i=0;i<10;i++){
            g.setColor(new Color(rm.nextInt(256),rm.nextInt(256),rm.nextInt(256)));
            g.drawLine(rm.nextInt(100), rm.nextInt(50), rm.nextInt(100), rm.nextInt(50));
        }

        //將驗證碼圖片回寫給瀏覽器
        response.setContentType("image/jpeg;charset=utf-8");
        OutputStream out=response.getOutputStream();
        ImageIO.write(img, "jpeg", out);

        //將隨機字符串保存在session中
        request.getSession().setAttribute("code", sb.toString());
    }

}

web-xml

 <servlet-name>CodeServlet</servlet-name>
    <servlet-class>com.yinhe.web.servlet.CodeServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>CodeServlet</servlet-name>
    <url-pattern>/checkCode</url-pattern>
  </servlet-mapping>
前臺頁面
  <script type="text/javascript">
  function loadImage(){                 document.getElementById("randImage").src = "${pageContext.request.contextPath}/image.jsp?"+Math.random(); //Math.random()方法非常重要，它使每次的請求都不同以便重新發送。如果每次的請求都一樣，那麼不會重新生成頁面   
      }
     </script>

<img src="checkCode" alt="" id="codeImg"
style="width: 80px; height: 30px; border: 1px solid black;" />
<a href="javascript:;" onclick="document.getElementById('codeImg').src = 'checkCode?'+(new Date()).getTime()">換一張</a>
<span id="codemsg" style="color: red; font-size: 20px;"></span>