绘制验证码的主要步骤：
1，设置宽度高度，验证码个数，干扰线个数，可选字符，背景颜色，字体格式
2，画干扰线，随机生成颜色，字体，字符
3，设置缓冲区，得到画笔，设置边框，读写数据，存储图片。
1,Servlet方法：
CheckCodeServlet类：
package org.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.OutputStream;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.http.HttpSession;
import sun.java2d.loops.DrawLine;
/**
* 输出随机的验证码
*/
@WebServlet({ "/CheckCode", "/checkCode.jpg" })
public class CheckCodeServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/* 宽度 */
private final int WIDTH = 200;
/* 高度 */
private final int HEIGHT = 40;
/* 生成验证码的个数 */
private final int COUNT = 4;
/* 干扰线条数 */
private final int LINE_ROW = 6;
/* 输出的基本码表，如果使用中文，则使用utf-8的码表，类似 ue234 ，而且应该使用常用字，避免出现偏僻字 */
private final char[] BASECODE = { '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', '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', '0', '1', '2', '3', '4', '5', '6', '7',
'8', '9' };
// 写出数据
private void write(HttpServletRequest request, HttpServletResponse response)
throws IOException {
HttpSession session = request.getSession();
BufferedImage image = new BufferedImage(WIDTH, HEIGHT,
BufferedImage.TYPE_INT_RGB);
Graphics graphics = image.getGraphics();
setBackground(graphics);
drawBorder(graphics);
drawDot(graphics);
drawLine(graphics);
drawString(graphics, session);
// 写出数据流
ImageIO.write(image, "jpg", response.getOutputStream());
}
// 写字
private void drawString(Graphics graphics, HttpSession session) {
StringBuffer sb = new StringBuffer();
Random random = new Random();
graphics.setFont(new Font("宋体", Font.BOLD, 18));
graphics.setColor(Color.BLACK);
for (int i = 0; i < COUNT; i++) {
String ch = String
.valueOf(BASECODE[random.nextInt(BASECODE.length)]);
sb.append(ch);
// 设置位置
int x = i * 20 + random.nextInt(12) + 10;
int y = random.nextInt(HEIGHT / 3) + 12;
// 旋转字体
double theta = Math.PI / 180 * random.nextInt(20);
// rotate(graphics, theta);
graphics.drawString(ch, x, y);
// 恢复。。
// rotate(graphics, -theta);
}
session.setAttribute("checkCode", sb.toString());
System.out.println(" 验证码：" + sb.toString());
}
// 旋转
private void rotate(Graphics graphics, double theta) {
((Graphics2D) graphics).rotate(theta);
}
// 画随机线条
private void drawLine(Graphics graphics) {
Random random = new Random();
for (int i = 0; i < LINE_ROW; i++) {
int x1 = random.nextInt(WIDTH);
int y1 = random.nextInt(HEIGHT);
int x2 = random.nextInt(WIDTH);
int y2 = random.nextInt(HEIGHT);
setRandomColor(graphics);
graphics.drawLine(x1, y1, x2, y2);
}
}
// 画斑点
private void drawDot(Graphics graphics) {
Random random = new Random();
graphics.setColor(Color.red);
for (int i = 0; i < WIDTH; i++) {
int x = i;
int y = random.nextInt(HEIGHT);
int r = random.nextInt(2);
// graphics.fillOval(x, y, r, r);
graphics.drawOval(x, y, r, r);
}
}
// 画边框
private void drawBorder(Graphics graphics) {
graphics.setColor(Color.BLACK);
graphics.drawRect(1, 1, WIDTH - 2, HEIGHT - 2);
}
// 设置背景
private void setBackground(Graphics graphics) {
graphics.setColor(Color.WHITE);
graphics.fillRect(0, 0, WIDTH, HEIGHT);// 填充背景色
}
// 设置随机的画笔颜色
private void setRandomColor(Graphics g) {
Random random = new Random();
g.setColor(new Color(random.nextInt(255), random.nextInt(255), random
.nextInt(255)));
}
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
// 输出图片流的头信息
response.setContentType("image/jpeg");
response.setHeader("Expires", "-1");
response.setHeader("Cache-Control", "no-cache");
// 写出数据
write(request, response);
}
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
}
2,XML文件配置：
将CheckCodeServlet写入配置。
3，jsp文件显示验证码：
<%@ page language="java" import="java.util.*" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<script type="text/javascript">
function flushCheckCode(obj) {
obj.src = (obj.src + '?' + new Date())
}
</script>
</head>
<body>
<form action="LoginServlet" method="post" align="center">
<table align="center">
<caption><p class="text1">用户登陆</p></caption>
<tr>
<td>
用户名：
</td>
<td>
<input name="username" type="text" placeholder="Userneme">
</td>
</tr>
<tr>
<td>
密 码:
</td>
<td>
<input name="password" type="password" placeholder="Password">
</td>
</tr>
<tr>
<td>
验证码：
</td>
<td>
<input type="text" name="checkCode" placeholder="CheckCode"/>
</td>
</tr>
</table>
<tr>
<td>
<img src="checkCode.jpg" onclick=flushCheckCode(this) alt="点击刷新验证码" />
</td>
</tr>
<br/>
<input name="submit" type="submit" class="button" value="登陆"/></br>
<p class="text2"><a href="register.jsp">没有账号？来注册一个吧！</a></font></p>
</form>
</body>
</html>