快乐编程

一般分为如下几个步骤（顺序可变）：

获取验证码
    前端：
    1.验证码在浏览器里，是一个img标签，将img的src设置为url请求即可
    后台：
    2.设置验证码中可能出现的字符
    3.画图片
        3.1创建BufferedImage对象
        3.2生成graphics对象
        3.3背景色
        3.4边框
        3.5干扰线
        3.6设置字体，画验证码
    4.设置response相关参数
    5.存session
    6.将图像输出到浏览器

检验验证码
    7.获取session中存储的字符串，进行验证
    8.如正确，将session中的存储清除

下面给出一个版本，可以点击下载

[java]
package org.fyc.test;

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

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

/**
*
* @author fyc 20110518
*
*/
public class CheckCodeGenerator {

private static final CheckCodeGenerator generator = new CheckCodeGenerator();

private final String ATTRIBUTE_NAME = "checkCode";
// 图片的宽度
private final int WIDTH = 15;
// 图片的高度
private final int HEIGHT = 22;
// 字符串长度
private final int CODE_LENGTH = 4;
// 随机字符串范围
private final String RAND_RANGE = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+ "1234567890";
private final char[] CHARS = RAND_RANGE.toCharArray();

private Random random = new Random();

private CheckCodeGenerator() {
//
}

public static CheckCodeGenerator getInstance() {
return generator;
}

/**
* 生成随机字符串
*
* @return 随机字符串
*/
private String getRandString() {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < CODE_LENGTH; i++)
sb.append(CHARS[random.nextInt(CHARS.length)]);
return sb.toString();
}

/**
* 生成随机颜色
*
* @param ll
* 产生颜色值下限(lower limit)
* @param ul
* 产生颜色值上限(upper limit)
* @return 生成的随机颜色对象
*/
private Color getRandColor(int ll, int ul) {
if (ll > 255)
ll = 255;
if (ll < 1)
ll = 1;
if (ul > 255)
ul = 255;
if (ul < 1)
ul = 1;
if (ul == ll)
ul = ll + 1;
int r = random.nextInt(ul – ll) + ll;
int g = random.nextInt(ul – ll) + ll;
int b = random.nextInt(ul – ll) + ll;
Color color = new Color(r, g, b);
return color;
}

/**
* 生成指定字符串的图像数据
*
* @param checkCode
* 即将被打印的随机字符串
* @return 生成的图像数据
* */
private BufferedImage getImage(String checkCode) {

BufferedImage image = new BufferedImage(WIDTH * CODE_LENGTH, HEIGHT,
BufferedImage.TYPE_INT_RGB);

// 获取图形上下文
Graphics graphics = image.getGraphics();

// 设置背景色
graphics.setColor(getRandColor(150, 230));
// 填充背景色
graphics.fillRect(0, 0, WIDTH * 4, HEIGHT);

// 设置边框颜色
graphics.setColor(new Color(245, 245, 245));
// 画边框
for (int i = 0; i < 2; i++)
graphics.drawRect(i, i, WIDTH * CODE_LENGTH – i * 2 – 1, HEIGHT – i
* 2 – 1);

// 设置随机干扰线条颜色
graphics.setColor(getRandColor(130, 160));
// 产生50条干扰线条
for (int i = 0; i < 50; i++) {
int x1 = random.nextInt(WIDTH * CODE_LENGTH – 4) + 2;
int y1 = random.nextInt(HEIGHT – 4) + 2;
int x2 = random.nextInt(WIDTH * CODE_LENGTH – 2 – x1) + x1;
int y2 = y1;
graphics.drawLine(x1, y1, x2, y2);
}

// 设置字体
graphics.setFont(new Font("Times New Roman", Font.PLAIN, 18));
// 画字符串
for (int i = 0; i < this.CODE_LENGTH; i++) {
String temp = checkCode.substring(i, i + 1);
graphics.setColor(getRandColor(10, 40));
graphics.drawString(temp, 13 * i + 6, 16);
}

// 图像生效
graphics.dispose();

return image;
}

/**
* 将验证码的图像输出
*
* @param request
* 用户的请求对象
* @param response
* 用户的响应对象
* */
public static void printImage(HttpServletRequest request,
HttpServletResponse response) {

// 将ContentType设为"image/jpeg"，让浏览器识别图像格式。
response.setContentType("image/jpeg");
// 设置页面不缓存
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 2000);

// 获得随机验证码
String checkCode = generator.getRandString();
// 获得验证码的图像数据
BufferedImage bi = generator.getImage(checkCode);
// 把验证码存入session
request.getSession().setAttribute(generator.ATTRIBUTE_NAME, checkCode);
try {
// 获得Servlet输出流
ServletOutputStream outStream = response.getOutputStream();
// 创建可用来将图像数据编码为JPEG数据流的编码器
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(outStream);
// 将图像数据进行编码
encoder.encode(bi);
// 强行将缓冲区的内容输入到页面
outStream.flush();
// 关闭输出流
outStream.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}

/**
* 检查输入的验证码是否正确
*
* @param request
* @return 验证结果
* */
public static String verify(HttpServletRequest request,
HttpServletResponse response) {
if (((String) request.getParameter(generator.ATTRIBUTE_NAME))
.equalsIgnoreCase((String) request.getSession().getAttribute(
generator.ATTRIBUTE_NAME))) {
request.getSession().removeAttribute(generator.ATTRIBUTE_NAME);
try {
response.getWriter().write("success");
} catch (IOException e) {
e.printStackTrace();
}
return "success";
} else {
try {
response.getWriter().write("error");
} catch (IOException e) {
e.printStackTrace();
}
return "error";
}
}
}

[/java]