<%@ page contenttype="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
<%!
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(255,255,255));
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
imageio.write(image, "jpeg", response.getoutputstream());
%>
