jsp页面验证码完整实例

package .servlet;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import .sun.image.codec.jpeg.JPEGCodec;
import .sun.image.codec.jpeg.JPEGImageEncoder;

public class IdentityServlet extends HttpServlet {

  public static final char[] chars={'2','3','4','5','6','7','8','9','A'};//自定义验证码池
  public static Random random=new Random();　　//随机数
  
  public static String getRandomString(){　　//获取6位随机数，放在图片里
    StringBuffer buffer=new StringBuffer();
    for(int i=0;i<6;i++){
      buffer.append(chars[random.nextInt(chars.length)]);
    }
    return buffer.toString();
  }
  
  public static Color getRandomColor(){　　//获取随机的颜色
    return new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255));
  }
  
  public static Color getReverseColor(Color c){　　//返回某颜色的反色
    return new Color(255 - c.getRed(), 255 - c.getGreen(), 255 - c.getBlue());
  }
  
  /
    Constructor of the object.
   /
  public IdentityServlet() {
    super();
  }

  /
    Destruction of the servlet. <br>
   /
  public void destroy() {
    super.destroy(); // Just puts "destroy" string in log
    // Put your code here
  }

  /
    The doGet method of the servlet. <br>
   
    This method is called when a form has its tag value method equals to get.
    
    @param request the request send by the client to the server
    @param response the response send by the server to the client
    @throws ServletException if an error ourred
    @throws IOException if an error ourred
   /
  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {

    response.setContentType("image/jpeg");　　//设置输出类型
    
    String randomString = getRandomString();　　//随机字符串
    request.getSession(true).setAttribute("randomString", randomString);//放到session里
    
    int width=100;　　//图片宽度
    int height=30;　　//图片高度
    
    Color color=getRandomColor();　　//随机颜色，用于背景色
    Color reverse=getReverseColor(color);//反色，用于前景色
    //创建一个彩色图片
    BufferedImage bi=new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    Graphics2D g=bi.createGraphics();　　//绘图对象
    g.setFont(new Font(Font.SANS_SERIF,Font.BOLD,16));//设置字体
    g.setColor(color);//设置颜色
    g.fillRect(0, 0, width, height);//绘制背景
    g.setColor(reverse);
    g.drawString(randomString, 18, 20);//绘制随机字符
    for(int i=0,n=random.nextInt(100);i<n;i++){　　//画最多100个噪音点
      g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);
    }
    ServletOutputStream out= response.getOutputStream();//转成JPEG格式
    JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);//编码器
    encoder.encode(bi);　　//对图片进行编码
    out.flush();　　//输出到客户端
  }

  /
    The doPost method of the servlet. <br>
   
    This method is called when a form has its tag value method equals to post.
    
    @param request the request send by the client to the server
    @param response the response send by the server to the client
    @throws ServletException if an error ourred
    @throws IOException if an error ourred
   /
  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {

    doGet(request, response);
  }

  /
    Initialization of the servlet. <br>
   
    @throws ServletException if an error ours
   /
  public void init() throws ServletException {
    // Put your code here
  }

}

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" 
  xmlns="http://java.sun./xml/ns/javaee" 
  xmlns:xsi="http://.w3./2001/XMLSchema-instance" 
  xsi:schemaLocation="http://java.sun./xml/ns/javaee 
  http://java.sun./xml/ns/javaee/web-app_3_0.xsd">
 <display-name></display-name>
 <servlet>
  <servlet-name>IdentityServlet</servlet-name>
  <servlet-class>.servlet.IdentityServlet</servlet-class>
 </servlet>

 <servlet-mapping>
  <servlet-name>IdentityServlet</servlet-name>
  <url-pattern>/servlet/IdentityServlet</url-pattern>
 </servlet-mapping>  
 <wele-file-list>
  <wele-file>index.jsp</wele-file>
 </wele-file-list>
</web-app>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://.w3./TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
function reloadImage(){
  document.getElementById('btn').disabled=true;
  document.getElementById('identity').src='servlet/IdentityServlet?ts='+new Date().getTime();
}
</script>
</head>

<body>

<img src="servlet/IdentityServlet" id="identity" onload="btn.disabled=false;" />
<input type=button value="换个图片" onclick="reloadImage()" id="btn">
</body>
</html>