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Java实现验证码

    博客分类：
  • Java
JavaServletJavaScriptCSSCache 
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编写一个Servlet

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class CheckCodeServlet extends HttpServlet {
    private static int WIDTH = 60;
    private static int HEIGHT = 20;

    public char[] generateCheckCode() {
        // 定义验证码的字符表
        String chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        char[] rands = new char[4];
        for (int i = 0; i < 4; i++) {
            int rand = (int) (Math.random() * 36);
            rands[i] = chars.charAt(rand);
        }
        return rands;
    }

    public void drawRands(Graphics g, char[] rands) {
        g.setColor(Color.BLACK);
        g.setFont(new Font(null, Font.ITALIC | Font.BOLD, 18));
        // 在不同的高度上输出验证码的每个字符
        g.drawString("" + rands[0], 1, 17);
        g.drawString("" + rands[1], 16, 15);
        g.drawString("" + rands[2], 31, 18);
        g.drawString("" + rands[3], 46, 16);
    }

    public void drawBackground(Graphics g) {
        // 画背景
        g.setColor(new Color(0xDCDCDC));
        g.fillRect(0, 0, WIDTH, HEIGHT);
        // 随机产生120个干扰点
        for (int i = 0; i < 120; i++) {
            int x = (int) (Math.random() * WIDTH);
            int y = (int) (Math.random() * HEIGHT);
            int red = (int) (Math.random() * 255);
            int green = (int) (Math.random() * 255);
            int blue = (int) (Math.random() * 255);
            g.setColor(new Color(red, green, blue));
            g.drawOval(x, y, 1, 0);
        }
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        HttpSession session = request.getSession();
        response.setContentType("image/jpeg");
        ServletOutputStream sos = response.getOutputStream();

        // 设置浏览器不缓存此图片
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);

        // 创建内存图像并获得其图形上下文
        BufferedImage image = new BufferedImage(WIDTH, HEIGHT,
                BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();

        // 产生随机的验证码
        char[] rands = generateCheckCode();

        // 产生图像
        drawBackground(g);
        drawRands(g, rands);

        // 结束图像的绘制过程,完成图像
        g.dispose();

        // 将图像输出到客户端
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ImageIO.write(image, "JPEG", bos);
        byte[] buf = bos.toByteArray();
        response.setContentLength(buf.length);
        sos.write(buf);
        bos.close();
        sos.close();

        // 将当前验证码存入到session中
        session.setAttribute("checkCode", new String(rands));
        System.out.println(session.getAttribute("checkCode"));
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

 编写一个html页面

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>test.html</title>
	
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="this is my page">
    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
    
    <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->
	<script type="text/javascript">
		function ajaxMethod(cid){
			document.getElementById(cid).setAttribute("src",null);
			//加上随机数的目的是为了每次都改变url 让浏览器不要加载缓存
			var svalue = "/JsParserXML/servlet/CheckCodeServlet?id=" + Math.random();
			document.getElementById(cid).setAttribute("src",svalue);				
		}
		function colorblue(id){
			document.getElementById(id).color="blue";
		}
		function colorblack(id){
			document.getElementById(id).color="black";
		}
	</script>
  </head>
  
  <body>
		<font size="2">验证码 :</font> 
		<img id="checkCodeImage" src="/JsParserXML/servlet/CheckCodeServlet" style="cursor:pointer" onclick="javascript:ajaxMethod('checkCodeImage');"/>
		<a style="cursor:pointer" onclick="javascript:ajaxMethod('checkCodeImage');"><font id="fontId" size="2"><u onmouseover="colorblue('fontId');" onmouseout="colorblack('fontId');">看不清换一个</u></font></a>
  </body>
</html>
 
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