生成一次验证码

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生成一次验证码

做JavaWeb有一项技能是必须掌握的，那就是生成一次验证码，在一点程序上防止恶意登陆和注册等。

这里只写服务端代码，而且生成的验证码简单，较易被机器识别。

下面是例子程序：

package com.heima;import java.awt.Color;import java.awt.Font;import java.awt.Graphics2D;import java.awt.image.BufferedImage;import java.io.IOException;import java.io.OutputStream;import java.util.Random;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.sun.image.codec.jpeg.JPEGCodec;import com.sun.image.codec.jpeg.JPEGImageEncoder;public class IdentifyingCode extends HttpServlet {private static final long serialVersionUID = 3281595309084322989L;private static final char[] CHARS = {'2', '3', '4', '5', '6', '7', '8', '9','A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};//生成的随机字符串，不包含0O1I等难以分辨的字符//生成随机数工具private static Random ran = new Random();//得到随机的字符串，将来显示到图片上private static String getRandomString() {StringBuilder builder = new StringBuilder();for (int i = 0; i < 4; i++) {builder.append(CHARS[ran.nextInt(CHARS.length)]);}return builder.toString();}//得到随机的颜色，用来当作生成图片的背景色private static Color getRandomColor() {return new Color(ran.nextInt(255), ran.nextInt(255), ran.nextInt(255));}//取背景色的反色，用来作为字体的颜色，背景与字体对比比较明显private static Color getReverseColor(Color c) {return new Color(255-c.getRed(), 255-c.getGreen(), 255-c.getBlue());}public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//设置文件类型response.setContentType("image/jpeg");//将得到的随机字符串放入session中，等待验证String ranString = getRandomString();request.getSession().setAttribute("identifyingCode", ranString);int width = 100;//生成图片的宽int height = 30;//生成图片的高Color c = getRandomColor();Color cr = getReverseColor(c);//图片BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);Graphics2D graphics = image.createGraphics();graphics.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 30));graphics.setColor(c);graphics.fillRect(0, 0, width, height);graphics.setColor(cr);graphics.drawString(ranString, 8, 26);//随机画50到100个干扰点for (int i=0,n=ran.nextInt(50)+50; i < n; i++) {graphics.drawRect(ran.nextInt(width), ran.nextInt(height), 1, 1);}//随机画5到20条与字体相同颜色的干扰线for (int i=0,n=ran.nextInt(15)+5; i < n; i++) {int x1 = ran.nextInt(width);int x2 = ran.nextInt(width);int y1 = ran.nextInt(height);int y2 = ran.nextInt(height);graphics.drawLine(x1, y1, x2, y2);}OutputStream out = response.getOutputStream();JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);encoder.encode(image);out.flush();}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {this.doGet(request, response);}}

使用时只需将图片的src属性指向这个servlet，就可以得到一个一次的随机验证码，只要在提交表单的时候从session中取出identifyingCode进行验证即可。

<script type="text/javascript">function change(){var img = document.getElementById("checkcode");img.src="/day09/checkCode?time="+new Date().getTime();}</script>

在调用servlet时加入时间戳，强制刷新图片，这样的效果看起来好像还可以，可以满足一般性需要

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