java web开发之servlet图形验证码功能的实现

package com.phome.util;import java.awt.Color;import java.awt.Font;import java.awt.Graphics2D;import java.awt.image.BufferedImage;import java.io.IOException;import java.util.Random;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.sun.image.codec.jpeg.JPEGCodec;import com.sun.image.codec.jpeg.JPEGImageEncoder;public class VerifyImgServlet extends HttpServlet {  private static final long serialVersionUID = 1L; // 设置随机字符字典。其中不包含0,o,1,I等难以辨认的字符 public static final char[] CHARS = { '2', '3', '4', '5', '6', '7', '8',   '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M',   'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a',   'b', 'c', 'd', 'e', 'f', 'g', 'h', 'j', 'k', 'l', 'm', 'n', 'p',   'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z' }; public static Random random = new Random(); // 随机数对象 public static String getRandomString() {  StringBuffer buffer = new StringBuffer(); // 字符串缓存  for (int i = 0; i < 6; i++) // 六次循环获取字符  {   buffer.append(CHARS[random.nextInt(CHARS.length)]); // 每次随机取一个字符  }  return buffer.toString(); } public static Color getRandomColor() {  return new Color(random.nextInt(255), random.nextInt(255),    random.nextInt(255)); } public static Color getReverseColor(Color c) {  return new Color(255 - c.getRed(), 255 - c.getGreen(),    255 - c.getBlue()); } public void doGet(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  response.setContentType("image/jpeg"); // 设置输出类型 不可省略  String randomString = getRandomString(); // 调用生成随机字符串方法获取并接受随机字符串  request.getSession(true).setAttribute("randomString", randomString); // 将字符串存储到Session中  int width = 100; // 图片宽度  int height = 30; // 图片高度  Color color = getRandomColor(); // 获取随机颜色 用于背景色  Color reverse = getReverseColor(color); // 反色 用于前景色  BufferedImage bi = new BufferedImage(width, height,    BufferedImage.TYPE_INT_RGB); // 创建一个彩色图片  Graphics2D g = bi.createGraphics(); // 获取绘图对象  g.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 16)); // 设置字体  g.setColor(color); // 设置颜色  g.fillRect(0, 0, width, height); // 绘制背景  g.setColor(reverse); // 设置颜色  g.drawString(randomString, 18, 20); // 绘制随机字符  for (int i = 0, n = random.nextInt(100); i < n; i++) // 画最多一百个噪音点  {   g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1); // 随机噪音点  }  ServletOutputStream out = response.getOutputStream(); // 好像是获取输出流  JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out); // 编码器  encoder.encode(bi); // 对图片进行编码  out.flush(); // 输出到客户端 } public void doPost(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  this.doGet(request, response); }}