JSP 动态验证码。

//validationCode类。

package com.validationCode; 

import java.awt.Color; 
import java.awt.Font; 
import java.awt.Graphics; 
import java.awt.image.BufferedImage; 
import java.io.ByteArrayOutputStream; 
import java.io.IOException; 
import java.util.Random; 

import javax.imageio.ImageIO; 
import javax.servlet.ServletException; 
import javax.servlet.ServletOutputStream; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
import javax.servlet.http.HttpSession; 

public class ValidateCodeServlet extends HttpServlet { 
private static final long serialVersionUID = 1L; 

private static int WIDTH = 65;//设置图片的宽度 

private static int HEIGHT = 22;//设置图片的高度 

public void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException { 
HttpSession session = request.getSession(); 
response.setContentType("image/jpeg"); 
ServletOutputStream sos = response.getOutputStream(); 

response.setHeader("Pragma", "No-cache"); 
response.setHeader("Cache-Control", "no-cache"); 
response.setDateHeader("Expires", 0); 

BufferedImage image = new BufferedImage(WIDTH, HEIGHT, 
BufferedImage.TYPE_INT_RGB); 
Graphics g = image.getGraphics(); 

char[] rands = generateCheckCode(); 
drawBackground(g); 
drawRands(g, rands); 
g.dispose(); 

ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
ImageIO.write(image, "JPEG", bos); 
byte[] buf = bos.toByteArray(); 
response.setContentLength(buf.length); 
sos.write(buf); 
bos.close(); 
sos.close(); 
session.setAttribute("randomCode", new String(rands)); 
} 

private void drawBackground(Graphics g) { 
g.setColor(new Color(0xDCDCDC)); 
g.fillRect(0, 0, WIDTH, HEIGHT); 
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); 
} 
} 

private void drawRands(Graphics g, char[] rands) { 
// g.setColor(Color.BLUE); 
Random random = new Random(); 
int red = random.nextInt(110); 
int green = random.nextInt(50); 
int blue = random.nextInt(50); 
g.setColor(new Color(red, green, blue)); 
g.setFont(new Font(null, Font.ITALIC | Font.BOLD, 18)); 
g.drawString("" + rands[0], 1, 17); 
g.drawString("" + rands[1], 16, 15); 
g.drawString("" + rands[2], 31, 18); 
g.drawString("" + rands[3], 46, 16); 
} 

private char[] generateCheckCode() { 
String chars = "13456789ABCDEFGHIJKLMNPQRSTUVWXY"; 
char[] rands = new char[4]; 
for (int i = 0; i < 4; i++) { 
int rand = (int) (Math.random() * 32); 
rands[i] = chars.charAt(rand); 
} 
return rands; 
} 

public void doPost(HttpServletRequest request, HttpServletResponse response) 
throws ServletException, IOException { 
this.doGet(request, response); 
} 
}

//在servlet中判断输入验证码是否正确

 

validate=request.getParameter("random");
HttpSession session = request.getSession();
String randomCode = (String)session.getAttribute("randomCode");

if(validate.equalsIgnoreCase(randomCode)){
//如果正确就。。。。。
}
else{
request.getSession().setAttribute("errorMessage",
"验证码不匹配，请重新输入验证码!");
}

//jsp页面

<script  language="javascript">

function changeCode() 
{ 
document.getElementById('rc').src="imgcode?t="+new Date().getTime();

}

</script>

<div>
<img src="imgcode" id="rc"/> 
<input type="text" name="random" maxlength="4"/> 
<a href="javascript:changeCode();">看不清？单击换一张图片</a> 
</div>

//web.xml

 

<servlet> 
<servlet-name>ValidateCodeServlet</servlet-name> 
<servlet-class>com.validationCode.ValidateCodeServlet</servlet-class> 
</servlet> 
<servlet-mapping> 
<servlet-name>ValidateCodeServlet</servlet-name> 
<url-pattern>/imgcode</url-pattern> 
</servlet-mapping>