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

public class RadomCodeServlet extends HttpServlet
{

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

?public void doPost(HttpServletRequest request, HttpServletResponse response)
???throws ServletException, IOException {
??//設置頁面不緩存
??response.setHeader("Pragma","No-cache");
??response.setHeader("Cache-Control","no-cache");
??response.setDateHeader("Expires", 0);
??//在內存中創建圖象
??int width=60, height=20;
??BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

??//獲取圖形上下文
??Graphics g = image.getGraphics();

??//生成隨機類
??Random random = new Random();

??//設定背景色
??g.setColor(getRandColor(200,250));
??g.fillRect(0, 0, width, height);

??//設定字體
??g.setFont(new Font("Times New Roman",Font.PLAIN,18));
??
??//隨機產生155條干擾線，使圖象中的認證碼不易被其它程序探測到
??g.setColor(getRandColor(160,200));
??for (int i=0;i<155;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);
??}
??
??//取隨機產生的認證碼(4位數字)
??String sRand="";
??for (int i=0;i<4;i++)
??{
????? String rand=String.valueOf(random.nextInt(10));
????? sRand+=rand;
????? // 將認證碼顯示到圖象中
????? g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+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(rand,13*i+6,16);
??}

??//將認證碼存入SESSION
??request.getSession().setAttribute("rand",sRand);

??//圖象生效
??g.dispose();

??//輸出圖象到頁面
??ImageIO.write(image, "JPEG", response.getOutputStream());??
?}
?
?//給定范圍獲得隨機顏色
?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);
??? }
?調用:
?<td height="25">
????????????<div align="right">
?????????????<font color="#000000">驗證碼：</font>
????????????</div>
???????????</td>
???????????<td align="left">
????????????<input type="text" name="randCode" size=10></input>
????????????<img style="cursor:hand" name="validatecode"
?????????????src=" servlet/RadomCodeServlet" height="17" align="middle"
?????????????onclick="document.validatecode.src=' servlet/RadomCodeServlet'">
???????????</td>