对于一些恶意强暴破解密码的行为（即通过硬性尝试用户名密码进行破解），可以采用验证码对其进行抵御，对于一些程序可以识别验证码，则需要对验证码形式进行多样化设计。
用户登录时设置验证码代码实现：
页面
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<script type=
"text/javascript"
>
function _change() {
var imgEle = document.getElementById(
"img"
);
imgEle.src =
"${pageContext.request.contextPath }/user_getVerify.action?a="
+
new
Date().getTime();
}
</script>
<BODY>
<FORM id=form1 name=form1 action=
"${pageContext.request.contextPath }/user_login.action"
method=
"post"
>
<TR>
<TD style=
"HEIGHT: 28px"
>验证码：</TD>
<TD style=
"HEIGHT: 28px"
>
<input type=
"text"
name=
"verifyCode"
size=
"1"
/>
<img id=
"img"
src=
"${pageContext.request.contextPath }/user_getVerify.action"
>
<br/>
<a href=
"javascript:_change()"
>换一张</a>
</TD>
<a href=
"#"
></a>
<TD style=
"HEIGHT: 28px"
><SPAN id=RequiredFieldValidator4
style=
"FONT-WEIGHT: bold; VISIBILITY: hidden; COLOR: white"
>请输入验证码</SPAN></TD></TR>
<TR>
</FORM></BODY>
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2.action操作
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//获得验证码
public
void
getVerify()
throws
IOException{
HttpServletRequest request=ServletActionContext.getRequest();
HttpServletResponse response=ServletActionContext.getResponse();
VerifyCode vc=
new
VerifyCode();
BufferedImage image=vc.getImage();
//获得图片
request.getSession().setAttribute(
"session_vcode"
,vc.getText());
//将验证码内容放在域对象里面
VerifyCode.output(image, response.getOutputStream());
}
public
String login(){
HttpServletRequest request=ServletActionContext.getRequest();
String sessionCode = (String) request.getSession().getAttribute(
"session_vcode"
);
String paramCode = request.getParameter(
"verifyCode"
);
if
(!paramCode.equalsIgnoreCase(sessionCode)){
request.setAttribute(
"msg"
,
"验证码错误！"
);
return
"login"
;
}
User userExit=userService.login(user);
if
(userExit!=
null
){
if
(!userExit.isState())
{
request.setAttribute(
"msg"
,
"您尚未激活，请到邮箱"
+userExit.getEmail()+
"激活！"
);
return
"loginerror"
;
}
request=ServletActionContext.getRequest();
request.getSession().setAttribute(
"user"
, userExit);
return
"loginsuccess"
;
}
else
{
return
"login"
;
}
}
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3.验证码代码实现
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import
java.awt.BasicStroke;
import
java.awt.Color;
import
java.awt.Font;
import
java.awt.Graphics2D;
import
java.awt.image.BufferedImage;
import
java.io.IOException;
import
java.io.OutputStream;
import
java.util.Random;
import
javax.imageio.ImageIO;
public
class
VerifyCode {
private
int
w =
70
;
private
int
h =
35
;
private
Random r =
new
Random();
// {"宋体", "华文楷体", "黑体", "华文新魏", "华文隶书", "微软雅黑", "楷体_GB2312"}
private
String[] fontNames = {
"宋体"
,
"华文楷体"
,
"黑体"
,
"微软雅黑"
,
"楷体_GB2312"
};
// 可选字符
private
String codes =
"23456789abcdefghjkmnopqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ"
;
// 背景色
private
Color bgColor =
new
Color(
255
,
255
,
255
);
// 验证码上的文本
private
String text ;
// 生成随机的颜色
private
Color randomColor () {
int
red = r.nextInt(
150
);
int
green = r.nextInt(
150
);
int
blue = r.nextInt(
150
);
return
new
Color(red, green, blue);
}
// 生成随机的字体
private
Font randomFont () {
int
index = r.nextInt(fontNames.length);
String fontName = fontNames[index];
//生成随机的字体名称
int
style = r.nextInt(
4
);
//生成随机的样式, 0(无样式), 1(粗体), 2(斜体), 3(粗体+斜体)
int
size = r.nextInt(
5
) +
24
;
//生成随机字号, 24 ~ 28
return
new
Font(fontName, style, size);
}
// 画干扰线
private
void
drawLine (BufferedImage image) {
int
num =
3
;
//一共画3条
Graphics2D g2 = (Graphics2D)image.getGraphics();
for
(
int
i =
0
; i < num; i++) {
//生成两个点的坐标，即4个值
int
x1 = r.nextInt(w);
int
y1 = r.nextInt(h);
int
x2 = r.nextInt(w);
int
y2 = r.nextInt(h);
g2.setStroke(
new
BasicStroke(
1
.5F));
g2.setColor(Color.BLUE);
//干扰线是蓝色
g2.drawLine(x1, y1, x2, y2);
//画线
}
}
// 随机生成一个字符
private
char
randomChar () {
int
index = r.nextInt(codes.length());
return
codes.charAt(index);
}
// 创建BufferedImage
private
BufferedImage createImage () {
BufferedImage image =
new
BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
Graphics2D g2 = (Graphics2D)image.getGraphics();
g2.setColor(
this
.bgColor);
g2.fillRect(
0
,
0
, w, h);
return
image;
}
// 调用这个方法得到验证码
public
BufferedImage getImage () {
BufferedImage image = createImage();
//创建图片缓冲区
Graphics2D g2 = (Graphics2D)image.getGraphics();
//得到绘制环境
StringBuilder sb =
new
StringBuilder();
//用来装载生成的验证码文本
// 向图片中画4个字符
for
(
int
i =
0
; i <
4
; i++) {
//循环四次，每次生成一个字符
String s = randomChar() +
""
;
//随机生成一个字母
sb.append(s);
//把字母添加到sb中
float
x = i *
1
.0F * w /
4
;
//设置当前字符的x轴坐标
g2.setFont(randomFont());
//设置随机字体
g2.setColor(randomColor());
//设置随机颜色
g2.drawString(s, x, h-
5
);
//画图
}
this
.text = sb.toString();
//把生成的字符串赋给了this.text
drawLine(image);
//添加干扰线
return
image;
}
// 返回验证码图片上的文本
public
String getText () {
return
text;
}
// 保存图片到指定的输出流
public
static
void
output (BufferedImage image, OutputStream out)
throws
IOException {
ImageIO.write(image,
"JPEG"
, out);
}
}
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4.效果
本文转自 叫我北北 51CTO博客，原文链接:http://blog.51cto.com/qinbin/1928345
