ＪＳＰ產生驗證碼

 <%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
<%!
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);
        }
%>
<%
//設定頁面不緩衝
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);

// 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();

//產生隨機類
Random random = new Random();

// 設定背景色
g.setColor(getRandColor(200,250));
g.fillRect(0, 0, width, height);

//設定字型
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155條幹擾線，使圖象中的認證碼不易被其它程式探測到
g.setColor(getRandColor(160,200));
for (int i=0;i<155;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位元字)
String sRand="";
for (int i=0;i<4;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，可能是因為種子太接近，所以只能直接產生
    g.drawString(rand,13*i+6,16);
}

// 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());


%> 


在linux不顯示，可以按以下方法修改

1.將jdk升級為jdk1.4，然後在java命令後加上運行參數 
–Djava.awt.headless=true.
tomcat是修改catalina.sh.
例子:
    "$_RUNJAVA" $JAVA_OPTS $CATALINA_OPTS /
      -Djava.endorsed.dirs="$JAVA_ENDORSED_DIRS" -classpath "$CLASSPATH" /
      -Dcatalina.base="$CATALINA_BASE" /
      -Dcatalina.home="$CATALINA_HOME" /
      -Djava.io.tmpdir="$CATALINA_TMPDIR" /
       -Djava.awt.headless=true /
      org.apache.catalina.startup.Bootstrap "$@" start /
      >> "$CATALINA_BASE"/logs/catalina.out 2>&1 &

2.使用第三方工具包。如pja包，下載地址  http://www.eteks.com/pja/en/#Download