纯JAVA技术验证码生成器（服务器端servlet实现）

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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;
/**
* @(#)VerifyCodeServlet.java Dec 9, 2007 8:14:14 PM
*
* @author Yuan
* 验证码生成器，使用此类需要将表单里的验证码输入框的name属性设为"verifycode"
*/
public class VerifyCodeGenerator {

private static final VerifyCodeGenerator generator = new VerifyCodeGenerator();

private final String ATTRIBUTE_NAME = "verifycode";
//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"
+ "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+ "1234567890"
+ "@#quot;;

private final char[] CHARS = RAND_RANGE.toCharArray();

private Random random = new Random();

private VerifyCodeGenerator(){
//
}

public static VerifyCodeGenerator 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 verifyCode 即将被打印的随机字符串
* @return 生成的图像数据
* */
private BufferedImage getImage(String verifyCode){

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(1,50));
//填充背景色
graphics.fillRect(0, 0, WIDTH * 4, HEIGHT);

//设置边框颜色
graphics.setColor(new Color(0,255,0));
//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(50,100));
//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 = verifyCode.substring(i, i+1);
graphics.setColor(getRandColor(100,255));
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 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 verifyCode = this.getRandString();
String str = "ssss";
for(int i=0; i<10; i++)
str = str + str;
//获得验证码的图像数据
BufferedImage bi = this.getImage(verifyCode);
//把验证码存入session
request.getSession().setAttribute(ATTRIBUTE_NAME, verifyCode);
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，若用户输入的验证码与生成的验证码相符则返回true，否则返回false。
* @param request 用户的请求对象
* @return 验证结果
* */
public boolean check(HttpServletRequest request){
if (((String)request.getParameter(ATTRIBUTE_NAME))
.equalsIgnoreCase((String)request.getSession().getAttribute(ATTRIBUTE_NAME))){
request.getSession().removeAttribute(ATTRIBUTE_NAME);
return true;
}
return false;
}
}<wbr></wbr><wbr></wbr>
/**此代码为深秋小雨所编写，来自J道**/

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摘自【http://www.blogjava.net/wuxingjia/archive/2008/04/05/190893.html】

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