java实现验证码

第一步：在web.xml中配置servlet

<servlet>
    <servlet-name>ImageServlet</servlet-name>
    <servlet-class>org.servlet.ImageServlet</servlet-class>
</servlet>
<servlet-mapping>
	<servlet-name>ImageServlet</servlet-name>
	<url-pattern>/ImageServlet</url-pattern>
</servlet-mapping>

第二步：ImageServlet实现

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.farm.web.tool.RandomValidateCode;

public class ImageServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("image/jpeg");// 设置相应类型,告诉浏览器输出的内容为图片
		response.setHeader("Pragma", "No-cache");// 设置响应头信息，告诉浏览器不要缓存此内容
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expire", 0);
		RandomValidateCode randomValidateCode = new RandomValidateCode();
		try {
			randomValidateCode.getRandcode(request, response);// 输出图片方法
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doGet(request, response);
	}

}

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

import javax.imageio.ImageIO;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class RandomValidateCode {

	public static String validateCode = null;
	public static final String RANDOMCODEKEY = "RANDOMVALIDATECODEKEY";// 放到session中的key
	private Random random = new Random();
	private String randString = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";// 随机产生的字符串

	private int width = 80;// 图片宽
	private int height = 26;// 图片高
	private int lineSize = 40;// 干扰线数量
	private int stringNum = 4;// 随机产生字符数量

	/*
	 * 获得字体
	 */
	private Font getFont() {
		return new Font("Fixedsys", Font.CENTER_BASELINE, 18);
	}

	/*
	 * 获得颜色
	 */
	private Color getRandColor(int fc, int bc) {
		if (fc > 255)
			fc = 255;
		if (bc > 255)
			bc = 255;
		int r = fc + random.nextInt(bc - fc - 16);
		int g = fc + random.nextInt(bc - fc - 14);
		int b = fc + random.nextInt(bc - fc - 18);
		return new Color(r, g, b);
	}

	/**
	 * 生成随机图片
	 */
	public void getRandcode(HttpServletRequest request,
			HttpServletResponse response) {
		HttpSession session = request.getSession();
		// BufferedImage类是具有缓冲区的Image类,Image类是用于描述图像信息的类
		BufferedImage image = new BufferedImage(width, height,
				BufferedImage.TYPE_INT_BGR);
		Graphics g = image.getGraphics();// 产生Image对象的Graphics对象,改对象可以在图像上进行各种绘制操作
		g.fillRect(0, 0, width, height);
		g.setFont(new Font("Times New Roman", Font.ROMAN_BASELINE, 18));
		g.setColor(getRandColor(110, 133));
		// 绘制干扰线
		for (int i = 0; i <= lineSize; i++) {
			drowLine(g);
		}
		// 绘制随机字符
		String randomString = "";
		for (int i = 1; i <= stringNum; i++) {
			randomString = drowString(g, randomString, i);
		}
		session.removeAttribute(RANDOMCODEKEY);
		session.setAttribute(RANDOMCODEKEY, randomString);
		validateCode = randomString.toUpperCase();
		g.dispose();
		try {
			ImageIO.write(image, "JPEG", response.getOutputStream());// 将内存中的图片通过流动形式输出到客户端
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	/*
	 * 绘制字符串
	 */
	private String drowString(Graphics g, String randomString, int i) {
		g.setFont(getFont());
		g.setColor(new Color(random.nextInt(101), random.nextInt(111), random
				.nextInt(121)));
		String rand = String.valueOf(getRandomString(random.nextInt(randString
				.length())));
		randomString += rand;
		g.translate(random.nextInt(3), random.nextInt(3));
		g.drawString(rand, 13 * i, 16);
		return randomString;
	}

	/*
	 * 绘制干扰线
	 */
	private void drowLine(Graphics g) {
		int x = random.nextInt(width);
		int y = random.nextInt(height);
		int xl = random.nextInt(13);
		int yl = random.nextInt(15);
		g.drawLine(x, y, x + xl, y + yl);
	}

	/*
	 * 获取随机的字符
	 */
	public String getRandomString(int num) {
		return String.valueOf(randString.charAt(num));
	}
}

第三步：jsp展现

<tr>
	<td>
		<div align="right">
			验证码：
		</div>
	</td>
	<td>
		<input style="width: 65px" id="validatecode" name="validatecode" type="text" />
	</td>
	<td>
		<img title="看不清楚,换一张？" style="cursor: pointer;"
			onclick="javascript:refresh(this);"
			src="<PF:basePath/>/ImageServlet">
	</td>
</tr>

src路径根据情况修改

function refresh(obj) {
	obj.src = "<PF:basePath/>/ImageServlet?"+Math.random();  
}

第四步：Action验证

if(RandomValidateCode.validateCode!=null&&validatecode.trim().toUpperCase().equals(RandomValidateCode.validateCode)){
	System.out.println("验证码正确");
}