Servlet实现验证码功能

package com.servlet;

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

public class Image extends HttpServlet {

	public void destroy() {

	}

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

		this.doPost(request, response);
	}

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

		// 设置编码格式
		response.setContentType("image/jpeg");

		// 创建图片的大小
		int width = 85;
		int height = 20;

		// 创建一个img对象
		BufferedImage img = new BufferedImage(width, height,
				BufferedImage.TYPE_INT_RGB);

		Random ran = new Random();

		// 得到画笔
		Graphics g = img.getGraphics();
		// 设置画笔的样式
		Color c = g.getColor();
		Font f = g.getFont();

		g.setColor(Color.pink);// 设置背景色
		g.fillRect(0, 0, width, height); // 填充背景色

		// 文字的操作
		StringBuffer sb = new StringBuffer();

		g.setFont(new Font("黑体", Font.BOLD, 16));

		for (int i = 0; i < 4; i++) {

			g.setColor(new Color(ran.nextInt(100), ran.nextInt(100), ran
					.nextInt(100)));

			String num = String.valueOf(ran.nextInt(10));

			g.drawString(num, i * 20 + 10, 15);

			sb.append(num);
		}

		// 恢复默认的画笔
		g.setColor(c);
		g.setFont(f);

		// 给服务器保存验证码字符串
		request.getSession().setAttribute("yan", sb);

		// 缓存清空
		response.setHeader("Pragma", "no-store"); // 本地机是否产生缓存文件
		response.setDateHeader("expires", 0); // 生效时间
		response.setHeader("Pragma", "no-cache"); // 清空

		// 输出图片
		ImageIO.write(img, "jpeg", response.getOutputStream());
	}

}