Servlet生成验证码

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 com.sun.image.codec.jpeg.*;

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

/**
 * Servlet implementation class IdentityServlet
 */
public class IdentityServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public IdentityServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.setContentType("image/jpeg");
        String randomString = getRandomString();
        request.getSession(true).setAttribute("randomString", randomString);// put
                                                                            // into
                                                                            // session
        int width = 100;
        int height = 30;
        Color color = getRandomColor();// 随即颜色用于背景色
        Color reverse = getReverseColor(color);// 反色,用于前景色
        BufferedImage bi = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_BGR);// 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);
        g.fillRect(0, 0, width, height);// 绘制背景
        g.setColor(reverse);
        g.drawString(randomString, 18, 20);// 绘制随即字符
        for (int i = 0, n = random.nextInt(100); i < n; i++) {// 绘制最多100个噪点
            g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);
        }
        ServletOutputStream out = response.getOutputStream();
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);// 编码器
        encoder.encode(bi);// 对图片进行编码
        out.flush();
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

    public static final char[] CHARS = { '2', '3', '4', '5', '6', '7', '8',
            '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
            'M', 'N', 'R', 'P', 'Q', 'S', 'T', 'Y' };

    public static Random random = new Random();

    public static String getRandomString() { // get 6 random numbers
        StringBuffer buffer = new StringBuffer();
        for (int i = 0; i < 6; i++) {
            buffer.append(CHARS[random.nextInt(CHARS.length)]);
        }
        return buffer.toString();
    }

    public static Color getRandomColor() { // get random color
        return new Color(random.nextInt(255), random.nextInt(255),
                random.nextInt(255));
    }

    public static Color getReverseColor(Color c) { // get reverse color
        return new Color(255 - c.getRed(), 255 - c.getGreen(),
                255 - c.getBlue());
    }

}

# jdk1.6不推荐使用JPEGImageEncoder，使用时编译不了

      这个是eclipse的设置问题，它默认把这些受访问限制的API设成了ERROR，只要把Windows-Preferences-Java-Complicer-Errors/Warnings里面的Deprecated and restricted API中的Forbidden references(access rules)选为Warning就可以编译通过了。