jsp驗證碼

<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*,java.awt.geom.AffineTransform" %>
<%!
Color getRandColor(int fc,int bc){//給定範圍獲得隨機顏色
        Random random = new Random();
        if(fc>255) fc=255;
        if(bc>255) bc=255;
        int r=fc+random.nextInt(bc-fc);
        int g=fc+random.nextInt(bc-fc);
        int b=fc+random.nextInt(bc-fc);
        return new Color(r,g,b);
        }
%>
<%
//設置頁面不緩存
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);
// 在內存中創建圖象
int width=80, height=30;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
// 獲取圖形上下文
//Graphics g = image.getGraphics();
Graphics2D g = image.createGraphics();
//生成隨機類
Random random = new Random();
// 設定背景色
g.setColor(getRandColor(200,250));
g.fillRect(0, 0, width, height);
//設定字體
g.setFont(new Font("Times New Roman",Font.PLAIN,18));
//畫邊框
//g.setColor(new Color());
//g.drawRect(0,0,width-1,height-1);

// 隨機產生188條幹擾線，使圖象中的認證碼不易被其它程序探測到
g.setColor(getRandColor(160,200));
for (int i=0;i<188;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);
}
// 取隨機產生的認證碼(4-6位數字)
int rdm = (int)(Math.random()*3+4);

String sRand="";
for (int i=0;i<rdm;i++){
    String rand=String.valueOf(random.nextInt(10));
    sRand+=rand;
    // 將認證碼顯示到圖象中
    g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//調用函數出來的顏色相同，可能是因爲種子太接近，所以只能直接生成
    
    /*
     *圖片旋轉
     */
    
    AffineTransform at = new AffineTransform();
    int number = random.nextInt(3)-1;
    double role = number*random.nextDouble()*(Math.PI/2);
    at.setToRotation(role,10*i,16);
    
    g.setTransform(at);
    /*
     *圖片旋轉
     */
    g.drawString(rand,10*i,16);
}
// 將認證碼存入SESSION
session.setAttribute("rand",sRand);

// 圖象生效
g.dispose();
// 輸出圖象到頁面
ImageIO.write(image, "JPEG", response.getOutputStream());

%>