jsp驗證碼的常式

<%@ page contentType="image/jpeg" import="java.awt.*,
java.awt.image.*,java.util.*,javax.imageio.*" %>
<%
// 在記憶體中建立圖象
int width=60, height=20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);

// 擷取圖形上下文
Graphics g = image.getGraphics();

// 設定背景色
g.setColor(new Color(0xDCDCDC));
g.fillRect(0, 0, width, height);

//畫邊框
g.setColor(Color.black);
g.drawRect(0,0,width-1,height-1);

// 取隨機產生的認證碼(4位元字)
//String rand = request.getParameter("rand");
Random r = new Random();
String rand = (1000+r.nextInt(9999)) + "";

// 將認證碼存入SESSION
session.setAttribute("rand",rand);

// 將認證碼顯示到圖象中
g.setColor(Color.black);
Integer tempNumber = new Integer(rand);
String numberStr = tempNumber.toString();

g.setFont(new Font("Atlantic Inline",Font.PLAIN,18));
String Str = numberStr.substring(0,1);
g.drawString(Str,8,17);

Str = numberStr.substring(1,2);
g.drawString(Str,20,15);
Str = numberStr.substring(2,3);
g.drawString(Str,35,18);

Str = numberStr.substring(3,4);
g.drawString(Str,45,15);

// 隨機產生88個幹擾點，使圖象中的認證碼不易被其它程式探測到
Random random = new Random();
for (int i=0;i<20;i++)
{
int x = random.nextInt(width);
int y = random.nextInt(height);
g.drawOval(x,y,0,0);
}

// 圖象生效
g.dispose();

// 輸出圖象到頁面
ImageIO.write(image, "JPEG", response.getOutputStream());
%>