Java 验证码不显示图片

jiangeb 2009-02-18 11:10:46

大家好，我用了一个网上的产生登录验证码的类。已经部署好了，但是运行的时候图片没有产生，是一个红叉。我把这个类贴出来，大家帮看看，浪费大家时间了，谢谢！

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

import java.awt.*;

import java.awt.image.*;

import javax.imageio.ImageIO;

public class CheckCodeServlet extends HttpServlet

{

private static int WIDTH = 60;

private static int HEIGHT = 20;

public void doGet(HttpServletRequest request,HttpServletResponse response)

throws ServletException,IOException

{

HttpSession session = request.getSession();

response.setContentType("image/jpeg");

ServletOutputStream sos = response.getOutputStream();

// 设置浏览器不要缓存此图片

response.setHeader("Pragma","No-cache");

response.setHeader("Cache-Control","no-cache");

response.setDateHeader("Expires", 0);

// 创建内存图象并获得其图形上下文

BufferedImage image =

new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);

Graphics g = image.getGraphics();

// 产生随机的认证码

char [] rands = generateCheckCode();

// 产生图像

drawBackground(g);

drawRands(g,rands);

// 结束图像的绘制过程，完成图像

g.dispose();

// 将图像输出到客户端

ByteArrayOutputStream bos = new ByteArrayOutputStream();

ImageIO.write(image, "JPEG", bos);

byte [] buf = bos.toByteArray();

response.setContentLength(buf.length);

// 下面的语句也可写成： bos.writeTo(sos);

sos.write(buf);

bos.close();

sos.close();

// 将当前验证码存入到 Session 中

session.setAttribute("check_code",new String(rands));

// 直接使用下面的代码将有问题， Session 对象必须在提交响应前获得

//request.getSession().setAttribute("check_code",new String(rands));

}

private char [] generateCheckCode()

{

// 定义验证码的字符表

String chars = "0123456789abcdefghijklmnopqrstuvwxyz";

char [] rands = new char[4];

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

{

int rand = (int)(Math.random() * 36);

rands[i] = chars.charAt(rand);

}

return rands;

}

private void drawRands(Graphics g , char [] rands)

{

g.setColor(Color.BLACK);

g.setFont(new Font(null,Font.ITALIC|Font.BOLD,18));

// 在不同的高度上输出验证码的每个字符

g.drawString("" + rands[0],1,17);

g.drawString("" + rands[1],16,15);

g.drawString("" + rands[2],31,18);

g.drawString("" + rands[3],46,16);

System.out.println(rands);

}

private void drawBackground(Graphics g)

{

// 画背景

g.setColor(new Color(0xDCDCDC));

g.fillRect(0, 0, WIDTH, HEIGHT);

// 随机产生 120 个干扰点

for(int i=0; i<120; i++)

{

int x = (int)(Math.random() * WIDTH);

int y = (int)(Math.random() * HEIGHT);

int red = (int)(Math.random() * 255);

int green = (int)(Math.random() * 255);

int blue = (int)(Math.random() * 255);

g.setColor(new Color(red,green,blue));

g.drawOval(x,y,1,0);

}

}

}

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