package util; 
import java.awt.Color; 
import java.awt.Font; 
import java.awt.Graphics; 
import java.awt.image.BufferedImage; 
import java.io.IOException; 
import java.io.OutputStream; 
import java.io.PrintWriter; 
import java.util.Random; 
import javax.imageio.ImageIO; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
import javax.servlet.http.HttpSession; 
import javax.servlet.jsp.PageContext; 
import javax.servlet.jsp.tagext.BodyContent; 
import com.sun.image.codec.jpeg.JPEGCodec; 
import com.sun.image.codec.jpeg.JPEGImageDecoder; 
import com.sun.image.codec.jpeg.JPEGImageEncoder; 
public class CodeUtil extends HttpServlet { 
 public void service(HttpServletRequest request, HttpServletResponse response) 
   throws ServletException, IOException { 
  //System.out.println("哈哈哈"); 
  response.setContentType("image/jpeg"); 
  //设置页面不缓存 
  response.setHeader("Pragma", "No-cache"); 
  response.setHeader("Cache-Control", "no-cache");  
  response.setDateHeader("Expires", 0); 
  //在内存中创建图像 
  int width = 90; 
  int height = 35; 
  BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB); 
  //获取图形上下文 
  Graphics g = image.getGraphics(); 
  //随机类 
  Random random = new Random(); 
  //设定背景 
  g.setColor(getRandColor(200, 250)); 
  g.fillRect(0, 0, width, height); 
  //设定字体 
  g.setFont(new Font("Times New Roman",Font.PLAIN,30)); 
  //随机产生干扰线 
  g.setColor(getRandColor(160, 200));  
  for (int i = 0; i  100; 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);  
  } 
  //随机产生4位验证码 
  String[] codes = {"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z","a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"}; 
  String code = ""; 
  for(int i=0;i4;i++){ 
   String str = codes[random.nextInt(codes.length)]; 
   code += str; 
   // 将认证码显示到图象中 
   g.setColor(new Color(50 + random.nextInt(110), 20 + random.nextInt(110), 30 + 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(str, 18 * i +13, 27); //文字间距*i+距离左边距，上边距 
  } 
  HttpSession session=request.getSession(); 
  // 将认证码存入SESSION  
  session.setAttribute("code", code); 
  // 图象生效  
  g.dispose();  
  // 输出图象到页面  
  ImageIO.write(image, "JPEG", response.getOutputStream()); 
  //加上下面代码,运行时才不会出现java.lang.IllegalStateException: getOutputStream() has already been called ..........等异常 
  response.getOutputStream().flush(); 
  response.getOutputStream().close(); 
  response.flushBuffer(); 
 } 
 //获取随机颜色 
 private Color getRandColor(int fc,int bc){ 
  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); 
  } 
} 

package util; 
import java.io.IOException; 
import java.io.PrintWriter; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
import javax.servlet.http.HttpSession; 
public class CheckCodeUtil extends HttpServlet { 
 public void service(HttpServletRequest request, HttpServletResponse response) 
   throws ServletException, IOException { 
  request.setCharacterEncoding("utf-8"); 
  response.setContentType("text/html;charset=utf-8"); 
  PrintWriter out = response.getWriter(); 
  //从session获取验证码 
  HttpSession session=request.getSession(); 
  String code=session.getAttribute("code").toString(); 
  System.out.println(code); 
  //获取用户输入验证码 
  String input=request.getParameter("code"); 
  System.out.println(input); 
  if(code.equalsIgnoreCase(input)){ 
   //转发数据 
   request.setAttribute("result", "true"); 
   request.getRequestDispatcher("test/regist.jsp").forward(request, response); 
//   response.sendRedirect(request.getContextPath()+"/regist/regist.jsp"); 
  }else{ 
   request.setAttribute("result", "false"); 
   request.getRequestDispatcher("test/regist.jsp").forward(request, response); 
  } 
 } 
} 

%@ page session="true" pageEncoding="utf-8" contentType="text/html; charset=utf-8"%> 
!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 
html> 
 head> 
  meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 
  title>Insert title here/title> 
  script> 
   function showResult1(){ 
   alert('输入正确'); 
   } 
   function showResult2(){ 
   alert('输入错误'); 
   } 
  /script> 
 /head> 
 % 
  response.setContentType("text/html;charset=utf-8"); 
  request.setCharacterEncoding("utf-8"); 
  String path=request.getContextPath(); 
  if(request.getAttribute("result")!=null){ 
  String result=request.getAttribute("result").toString(); 
  out.print(result); 
  if(result.equals("true")){ 
   out.print("true"); 
   out.print("script>showResult1();script>"); 
  }else{ 
   out.print("script>showResult2();script>"); 
  } 
  } 
 %> 
  body> 
  br>验证码演示 
  form action="%=path %>/checkCodeUtil" method="post"> 
  input type="text" size="10" name="code"/> 
  img src="%=path %>/codeUtil" id="img"/> 
  a href="javascript:;" onclick="document. 
   getElementById('img').src='%=path %>/codeUtil?'+new Date().getTime();">看不清，换一个/a> 
  input type="submit" value="提交"> 
  /form> 
 /body> 
/html>