JSP实现验证码

<%@ page language="java" import="java.util.*" pageEncoding="GBK"%>
<%@ page import="java.awt.*,com.sun.image.codec.jpeg.*,java.awt.image.*" %>
<%@ page import="java.io.OutputStream" %>
<%
	final int W = 60;
	final int H = 25;
	final String[] CTable = ("1 2 3 4 5 6 7 8 9 " 
		+ "A B C D E F G H I J K L M N O P Q R S T U V W X Y Z").split(" ");
	
	BufferedImage img = new BufferedImage(W, H, BufferedImage.TYPE_INT_RGB);
	Graphics g = img.getGraphics();
	
	// 画背景
	g.setColor(Color.PINK);
	g.fillRect(0, 0, img.getWidth(), img.getHeight());
	
	// 画干扰线
	g.setColor(Color.GRAY);
	for (int i = 0; i < 20; i++) {
		g.drawLine(new Random().nextInt(W), new Random().nextInt(H), 
				new Random().nextInt(W), new Random().nextInt(H));
	}
	
	// 随机生成四个数
	g.setColor(Color.BLUE);
	g.setFont(new Font("Courier New", Font.BOLD, 16));
	for (int i = 0; i < 4; i++) {
		g.drawString(CTable[new Random().nextInt(35)], 6 + i * 13, 17);
	}
	
	// 向客户端输出
	response.setContentType("image/jpeg");
	OutputStream os = response.getOutputStream();
	try {
		JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(os);
		encoder.encode(img);
	}
	catch (Exception ex)  {
		// do nothing
	}
	finally {
		if (os != null) {
			os.close();
		}
	}
	out.clear();
	out = pageContext.pushBody();
%>