画矩形很容易实现，如何在其中添加文字呢？
------解决方案--------------------
用VML吧，操作代码用javascriopt，或者用applet
------解决方案--------------------
Servlet 中画三角形,以下为doget方法
图象编码用到com.sun.image.codec.jpeg.*;包
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.reset();
response.setContentType( "image/jpeg ");
int width=400,height=300;
BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
Graphics g =image.getGraphics();
g.setColor(Color.black);
g.drawRect(0,0,width,height);
g.setColor(Color.red);
g.drawString( "it is a string ",width-10,height+10);
ServletOutputStream out1 = response.getOutputStream();
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out1);
encoder.encode(image);
out1.close();
}
------解决方案--------------------
<%@ page language= "java " contentType= "text/html; charset=GBK "
pageEncoding= "GBK "%>
<%@ page import= "java.awt.*,java.awt.image.*,java.util.*,javax.imageio.* " %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN ">
<html>
<head>
<meta http-equiv= "Content-Type " content= "text/html; charset=GB18030 ">
<title> Insert title here </title>
</head>
<body>
<%!
Color getRandColor(int fc,int bc){//给定范围获得随机颜色
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);
}
%>
<%
//设置页面不缓存
response.setHeader( "Pragma ", "No-cache ");
response.setHeader( "Cache-Control ", "no-cache ");
response.setDateHeader( "Expires ", 0);
// 在内存中创建图象
int width=60, height=20;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
// 获取图形上下文
Graphics g = image.getGraphics();
//生成随机类
Random random = new Random();
// 设定背景色
g.setColor(getRandColor(200,250));
g.fillRect(0, 0, width, height);
//设定字体
g.setFont(new Font( "Times New Roman ",Font.PLAIN,18));
//画边框
//g.setColor(new Color());
//g.drawRect(0,0,width-1,height-1);
// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
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);
}
// 取随机产生的认证码(4位数字)
String sRand= " ";
for (int i=0;i <4;i++){
String rand=String.valueOf(random.nextInt(10));
sRand+=rand;
// 将认证码显示到图象中
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
g.drawString(rand,13*i+6,16);
}
// 将认证码存入SESSION
session.setAttribute( "rand ",sRand);
// 图象生效
g.dispose();
// 输出图象到页面
ServletOutputStream sos=response.getOutputStream();
ImageIO.write(image, "JPEG ", sos);