图形验证码的生成

/*
 * 功能说明：生成验证码图片，将验证码保存进session里
 * 参数说明：
 *         count:验证码的字符个数
 *         width:验证码图片宽度
 *         height:验证码图片高度
 *         type:类型 0-纯数字 1-纯大写字母 2-数字和大学字母混合
 */
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.imageio.ImageIO;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ValidationCodeServlet extends HttpServlet {
   
	private static final long serialVersionUID = 6777280022666782466L;

	private final int TYPE_NUMBER = 0;

    private final int TYPE_LETTER = 1;

    private final int TYPE_MULTIPLE = 2;

    private int width;

    private int height;

    private int count;

    private int type;

    private String validate_code;

    private Random random;

    private Font font;

    private int line;

    @Override
    public void init(ServletConfig config) throws ServletException {
	super.init(config);
	width = 56;
	height = 22;
	count = 4;
	type = TYPE_NUMBER;
	random = new Random();
	line = 200;
    }

    @Override
    protected void doGet(HttpServletRequest request,
	    HttpServletResponse response) throws ServletException, IOException {
	response.setHeader("Pragma", "No-cache");
	response.setHeader("Cache-Control", "no-cache");
	response.setDateHeader("Expires", 0);
	response.setContentType("image.jpeg");

	String reqCount = request.getParameter("count");
	String reqWidth = request.getParameter("width");
	String reqHeight = request.getParameter("height");
	String reqType = request.getParameter("type");

	if (reqCount != null && reqCount != "")
	    this.count = Integer.parseInt(reqCount);
	if (reqWidth != null && reqWidth != "")
	    this.width = Integer.parseInt(reqWidth);
	if (reqHeight != null && reqHeight != "")
	    this.height = Integer.parseInt(reqHeight);
	if (reqType != null && reqType != "")
	    this.type = Integer.parseInt(reqType);

	font = new Font("Courier New", Font.BOLD, width / count);

	BufferedImage image = new BufferedImage(width, height,
		BufferedImage.TYPE_INT_RGB);

	Graphics g = image.getGraphics();

	g.setColor(getRandColor(200, 250));
	g.fillRect(0, 0, width, height);

	g.setColor(getRandColor(160, 200));
	for (int i = 0; i < line; i++) {
	    int x = random.nextInt(width);
	    int y = random.nextInt(height);
	    int xl = random.nextInt(12);
	    int yl = random.nextInt(12);
	    g.drawLine(x, y, x + xl, y + yl);
	}

	g.setFont(font);
	validate_code = getValidateCode(count, type);
	request.getSession().setAttribute("validate_code", validate_code);
	for (int i = 0; i < count; i++) {
	    g.setColor(new Color(20 + random.nextInt(110), 20 + random
		    .nextInt(110), 20 + random.nextInt(110)));
	    int x = (width / count) * i;
	    int y = ((height + font.getSize()) / 2) - 5;
	    g.drawString(String.valueOf(validate_code.charAt(i)), x, y);
	}

	g.dispose();
	ImageIO.write(image, "JPEG", response.getOutputStream());
    }

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

    private Color getRandColor(int from, int to) {
	Random random = new Random();
	if (to > 255)
	    from = 255;
	if (to > 255)
	    to = 255;
	int rang = Math.abs(to - from);
	int r = from + random.nextInt(rang);
	int g = from + random.nextInt(rang);
	int b = from + random.nextInt(rang);
	return new Color(r, g, b);
    }

    private String getValidateCode(int size, int type) {
	StringBuffer validate_code = new StringBuffer();
	for (int i = 0; i < size; i++) {
	    validate_code.append(getOneChar(type));
	}
	return validate_code.toString();
    }

    private String getOneChar(int type) {
	String result = null;
	switch (type) {
	case TYPE_NUMBER:
	    result = String.valueOf(random.nextInt(10));
	    break;

	case TYPE_LETTER:
	    result = String.valueOf((char) (random.nextInt(26) + 65));
	    break;

	case TYPE_MULTIPLE:
	    if (random.nextBoolean()) {
		result = String.valueOf(random.nextInt(10));
	    } else {
		result = String.valueOf((char) (random.nextInt(26) + 65));
	    }
	    break;
	default:
	    result = null;
	    break;
	}
	if (result == null)
	    throw new NullPointerException("获取验证码出错");
	return result;
    }
}