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");   //設置頁面不緩存   response.setHeader("Pragma", "No-cache");   response.setHeader("Cache-Control", "no-cache");    response.setDateHeader("Expires", 0);   //在內存中創建圖像   int width = 90;   int height = 35;   BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);   //獲取圖形上下文   Graphics g = image.getGraphics();   //隨機類   Random random = new Random();   //設定背景   g.setColor(getRandColor(200, 250));   g.fillRect(0, 0, width, height);   //設定字體   g.setFont(new Font("Times New Roman",Font.PLAIN,30));   //隨機產生干擾線   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);    }   //隨機產生4位驗證碼   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;i<4;i++){    String str = codes[random.nextInt(codes.length)];    code += str;    // 將認證碼顯示到圖象中    g.setColor(new Color(50 + random.nextInt(110), 20 + random.nextInt(110), 30 + random.nextInt(110)));    //調用函數出來的顏色相同，可能是因為種子太接近，所以只能直接生成     g.drawString(str, 18 * i +13, 27); //文字間距*i+距離左邊距，上邊距   }   HttpSession session=request.getSession();   // 將認證碼存入SESSION    session.setAttribute("code", code);   // 圖象生效    g.dispose();    // 輸出圖象到頁面    ImageIO.write(image, "JPEG", response.getOutputStream());   //加上下面代碼,運行時才不會出現java.lang.IllegalStateException: getOutputStream() has already been called ..........等異常   response.getOutputStream().flush();   response.getOutputStream().close();   response.flushBuffer();  }  //獲取隨機顏色  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();   //從session獲取驗證碼   HttpSession session=request.getSession();   String code=session.getAttribute("code").toString();   System.out.println(code);   //獲取用戶輸入驗證碼   String input=request.getParameter("code");   System.out.println(input);   if(code.equalsIgnoreCase(input)){    //轉發數據    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('輸入正確');    }    function showResult2(){    alert('輸入錯誤');    }   </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>驗證碼演示   <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，換一個</a>   <input type="submit" value="提交">   </form>  </body> </html>