servlet 产生验证码
在网上每次注册或者登录的时候都要求用户输入验证码，今天我们来做一个吧。
private static final long serialVersionUID = 1L;
//用数组CHARs数组来保存所有能够产生的字符
public static final char[] CHARs={
'2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','J','K','L','M','N','P','Q','R','S','T','U','V','W','X','Y','Z'
};
public static Random random=new Random();
//下面是产生六个随机数
public static String getRandomString(){
StringBuffer buffer=new StringBuffer();
for(int i=0;i<6;i++){
buffer.append(CHARs[random.nextInt(CHARs.length)]);
}
return buffer.toString();
}
//用三个随机数来分别产生ＲＧＢ的数值
public static Color getRandomColor(){
return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255));
}
//产生反色的颜色
public static Color getgetReverseColor(Color c){
return new Color(255-c.getRed(),255-c.getGreen(),255-c.getBlue());
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("image/jpeg");//生成时的图像格式
String randomString=getRandomString();//获取随机数
request.getSession(true).setAttribute("randomString", randomString);
//生成的验证码图像的大小
int width=100;
int height=30;
Color color=getRandomColor();
Color reverse=getgetReverseColor(color);
BufferedImage bi=new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g=bi.createGraphics();
g.setFont(new Font(Font.SANS_SERIF,Font.BOLD,16));
g.setColor(color);
g.fillRect(0, 0, width, height);
g.setColor(reverse);
g.drawString(randomString, 18, 20);
//用来产生污点来防止被破解
for(int i=0,n=random.nextInt(100);i<n;i++){
g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);
}
ServletOutputStream out=response.getOutputStream();
JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);
encoder.encode(bi);
out.flush();
}
用一个HTML来测试结果
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
function reloadImage(){
document.getElementById('identity').src='servlet/IdentityServlet?ts='+new Date().getTime();
}
</script>
<img src="servlet/IdentityServlet" id="identity"/>
<input type="button" value="换个图片" onclick="reloadImage()" id="btn">
</head>
<body>
</body>
</html>
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