验证码图片生成步骤
创建BufferedImage对象。获取BufferedImage的画笔，即调用getGraphics()方法获取Graphics对象。调用Graphics对象的setColor()方法和fillRect()方法设置图片背景颜色。调用Graphics对象的setColor()方法和drawLine()方法设置图片干扰线。调用BufferedImaged对象的setRGB()方法设置图片的噪点。调用Graphics对象的setColor()方法、setFont()方法和drawString()方法设置图片验证码。因为验证码的图片的宽度和高度要根据网站的风格来确定的，所以字体的大小需要根据图片的宽度和高度来确定，用到了小小的技巧。
package util;import java.awt.Color;import java.awt.Font;import java.awt.Graphics;import java.awt.Image;import java.awt.image.BufferedImage;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.util.Random;import javax.imageio.ImageIO;public class Verification {private static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";/*** 生成一个宽为width， 高为height， 验证码为code的图片* @param width 图片的宽* @param height 图片的高* @param code 验证码字符串* @return 返回图片验证码*/public static BufferedImage getImage(int width, int height, String code){return getImage(width, height, code, 20);}/*** 生成一个宽为width， 高为height， 验证码为code的图片，图片中干扰线的条数为lineCnt* @param width 图片的宽* @param height 图片的高* @param code 验证码字符串* @param lineCnt 干扰线的条数，建议为10条左右，可根据结果适当调整* @return 返回图片验证码*/public static BufferedImage getImage(int width, int height, String code, int lineCnt){return createImage(width, height, code, lineCnt, 0.01);}/*** 生成一个宽为width， 高为height， 验证码为code的图片，图片中干扰线的条数为lineCnt* 噪声比为noiseRate，即图片中噪音像素点的百分比* @param width 图片的宽* @param height 图片的高* @param code 验证码字符串* @param lineCnt 干扰线的条数，建议为10条左右，可根据结果适当调整* @param noiseRate 图片中噪音像素点占总像素的百分比* @return 返回图片验证码*/public static BufferedImage getImage(int width, int height, String code, int lineCnt, double noiseRate){return createImage(width, height, code, lineCnt, noiseRate);}/*** * 生成一个宽为width， 高为height， 验证码为code的图片，图片中干扰线的条数为lineCnt* 噪声比为noiseRate，即图片中噪音像素点的百分比* @param width 图片的宽* @param height 图片的高* @param code 验证码字符串* @param lineCnt 干扰线的条数，建议为10条左右，可根据结果适当调整* @param noiseRate 图片中噪音像素点占总像素的百分比* @return 返回图片验证码*/private static BufferedImage createImage(int width, int height, String code, int lineCnt, double noiseRate){int fontWidth = ((int)(width * 0.8)) / code.length();int fontHeight = (int)(height * 0.7);//为了在任意的width和height下都能生成良好的验证码，//字体的大小为fontWdith何fontHeight中的小者，int fontSize = Math.min(fontWidth, fontHeight);//drawString时要用到int paddingX = (int) (width * 0.1);int paddingY = height - (height - fontSize) / 2;//创建图像BufferedImage buffimg = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);//获得画笔Graphics g = buffimg.getGraphics();//设置画笔的颜色g.setColor(getRandColor(200, 255));//然后填充一个矩形，即设置背景色g.fillRect(0, 0, width, height);// 设置干扰线for (int i = 0; i < lineCnt; i++) {//随机获取干扰线的起点和终点int xs = (int)(Math.random() * width);int ys = (int)(Math.random() * height);int xe = (int)(Math.random() * width);int ye = (int)(Math.random() * height);g.setColor(getRandColor(1, 255));g.drawLine(xs, ys, xe, ye);}// 添加噪点int area = (int) (noiseRate * width * height);for(int i=0; i<area; ++i){int x = (int)(Math.random() * width);int y = (int)(Math.random() * height);buffimg.setRGB(x, y, (int)(Math.random() * 255));}//设置字体Font font = new Font("Ravie", Font.PLAIN, fontSize);g.setFont(font);for(int i=0; i<code.length(); ++i){String ch = code.substring(i, i+1);g.setColor(getRandColor(1, 199));g.drawString(ch, paddingX + fontWidth * i, paddingY);}return buffimg;}/*** 获取随机的颜色，r,g,b的取值在L到R之间* @param L 左区间* @param R 右区间* @return 返回随机颜色值*/private static Color getRandColor(int L, int R){if(L > 255)L = 255;if(R > 255)R = 255;if(L < 0)L = 0;if(R < 0)R = 0;int interval = R - L; int r = L + (int)(Math.random() * interval);int g = L + (int)(Math.random() * interval);int b = L + (int)(Math.random() * interval);return new Color(r, g, b);}/*** 随机生成若干个由大小写字母和数字组成的字符串* @param len 随机生成len个字符* @return 返回随机生成的若干个由大小写字母和数字组成的字符串*/public static String getRandCode(int len){String code = "";for(int i=0; i<len; ++i){int index = (int)(Math.random() * ALPHABET.length());code = code + ALPHABET.charAt(index);}return code;}/*** 将图片转为byte数组* @param image 图片* @return 返回byte数组* @throws IOException*/public static byte[] getByteArray(BufferedImage image) throws IOException{ByteArrayOutputStream baos = new ByteArrayOutputStream();ImageIO.write(image, "png", baos);return baos.toByteArray();//ByteArrayOutputStream 不需要close }}
使用验证码图片
在verificationCode.java这个servlet中调用上面的类生成验证码图片，然后将图片返回给客户端。
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {HttpSession session = request.getSession();//随机生成字符串，并写入sessionString code = Verification.getRandCode(4);session.setAttribute("verification", code);BufferedImage image = util.Verification.getImage(100,30, code, 5);response.setContentType("image/png");OutputStream out = response.getOutputStream();out.write(util.Verification.getByteArray(image));out.flush();out.close();}
在index.jsp中设置验证码，用户点击验证码时，调用js代码请求服务器得到新的验证码。因为上面的那个生成验证码的servlet会被浏览器缓存，所以js代码中需要给该servlet一个随机的参数，这样浏览器就会向服务器发请求得到新的验证码，而不是去缓存中读取。
<%@page import="util.Verification"%><%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title><script type="text/javascript">function refreshcode(){document.getElementById("verification").src= "/verificationCode/verificationCode?hehe="+Math.random();}</script></head><body><form action="<%=request.getContextPath()+"/checkVerification" %>" method="post">验证码:<input type="text" name="submitVerification"><img id="verification" alt="" title="看不清点击刷新验证码" src="<%=request.getContextPath()+"/verificationCode" %>"οnclick="refreshcode()"><br><input type="submit" name="submit" value="提交"></form></body></html>
最后是在checkVerification.java这个servlet中判断用户输入的验证码是否正确，为了方便用户，验证码一般都设置成大小写不敏感，所以要先转化为小写字母再比对。
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {HttpSession session = request.getSession();String verification = (String)session.getAttribute("verification");String submitVerification = request.getParameter("submitVerification");PrintWriter out = response.getWriter();if(verification!=null && submitVerification!=null){if(verification.toLowerCase().equals(submitVerification.toLowerCase())){out.println("yes!!!");}else{out.println("no!!!");}}else{out.println("no!!!");}session.removeAttribute("verification");//防止用户重复提交表单}/*** @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)*/protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stub doGet(request, response);}
最后运行的效果图如下
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