该JSP可以生成验证码。以后用到的时候就方便了。

<%@ page language="java" pageEncoding="UTF-8"%>

<%@ page contentType="image/jpeg"  import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>

<%!

    public Color getColor(){

        Random random = new Random();

        int r = random.nextInt(256);//0-255

        int g = random.nextInt(256);

        int b = random.nextInt(256);

        return new Color(r,g,b);

    }

    public String getNum(){

        String str = "";

        Random random = new Random();

        for(int i=0;i<4;i++){

            str += random.nextInt(10);//0-9

        }

        return str;

    }

%>

<%

    response.setHeader("pragma", "mo-cache");

    response.setHeader("cache-control", "no-cache");

    response.setDateHeader("expires", 0);

    BufferedImage image = new BufferedImage(80,30,BufferedImage.TYPE_INT_RGB);

    Graphics g = image.getGraphics();

    g.setColor(new Color(200,200,200));

    g.fillRect(0,0,80,30);

    for (int i = 0; i < 30; i++) {

        Random random = new Random();

        int x = random.nextInt(80);

        int y = random.nextInt(30);

        int xl = random.nextInt(x+10);

        int yl = random.nextInt(y+10);

        g.setColor(getColor());

        g.drawLine(x, y, x + xl, y + yl);

    }

    g.setFont(new Font("serif", Font.BOLD,16));

    g.setColor(Color.BLACK);

    String checkNum = getNum();//"2525"

    StringBuffer sb = new StringBuffer();

    for(int i=0;i<checkNum.length();i++){

        sb.append(checkNum.charAt(i)+" ");//"2 5 2 5"

    }

    g.drawString(sb.toString(),15,20);

    session.setAttribute("CHECKNUM",checkNum);//2525

    ImageIO.write(image,"jpeg",response.getOutputStream());

    out.clear();

    out = pageContext.pushBody();

%>