Servlet获取简单验证码

 package com.helloweenvsfei.servlet;

 import java.awt.Color;
 import java.awt.Font;
 import java.awt.Graphics2D;
 import java.awt.image.BufferedImage;
 import java.io.IOException;
 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 com.sun.image.codec.jpeg.JPEGCodec;
 import com.sun.image.codec.jpeg.JPEGImageEncoder;

 public class IdentityServlet extends HttpServlet{
     public static final char[] CHARS={
         '2', '3', '4', '5', '6', '7', '8',
         '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M',
         'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'
     };
     public static Random random =new Random();

     public static String getRandomString(){
         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() {
         return new Color(random.nextInt(255), random.nextInt(255), random
                 .nextInt(255));
     }

     public static Color getReverseColor(Color c) {
         return new Color(255 - c.getRed(), 255 - c.getGreen(), 255 - c
                 .getBlue());
     }
     public void doGet(HttpServletRequest request,HttpServletResponse response)
     throws ServletException, IOException {
         response.setContentType("image/jpeg");
         String randomString = getRandomString();
         request.getSession(true).setAttribute("randomString", randomString);

         int width = 100;
         int height = 30;

         Color color = getRandomColor();
         Color reverse = getReverseColor(color);
         BufferedImage bi = new BufferedImage(width, height,
                 BufferedImage.TYPE_INT_RGB);
         Graphics2D g = bi.createGraphics();
         g.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 20));
         g.setColor(color);
         g.fillRect(0, 0, width, height);
         g.setColor(reverse);
         g.drawString(randomString, 18, 20);
         for (int i = 0, n = random.nextInt(100); i < n; i++) {
             g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);
         }

         // 转成JPEG格式
         ServletOutputStream out = response.getOutputStream();
         JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
         encoder.encode(bi);
         out.flush();
     }

     public static void main(String[] args) {
         System.out.println(getRandomString());
     }
 }

IdentityServlet.java

 <?xml version="1.0" encoding="UTF-8"?>
 <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
     http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
     <servlet>
         <servlet-name>FirstServlet</servlet-name>
         <servlet-class>com.helloweenvsfei.servlet.FirstServlet</servlet-class>
         <init-param>
             <param-name>message</param-name>
             <param-value>welcome to FirstServlet</param-value>
         </init-param>
         <init-param>
             <param-name>encoding</param-name>
             <param-value>utf-8</param-value>
         </init-param>
         <load-on-startup>1</load-on-startup>
     </servlet>
     <servlet>
         <servlet-name>RequestServlet</servlet-name>
         <servlet-class>com.helloweenvsfei.servlet.RequestServlet</servlet-class>
     </servlet>
       <servlet>
     <servlet-name>IdentityServlet</servlet-name>
     <servlet-class>com.helloweenvsfei.servlet.IdentityServlet</servlet-class>
   </servlet>
     <servlet-mapping>
         <servlet-name>FirstServlet</servlet-name>
         <url-pattern>/servlet/FirstServlet</url-pattern>
         <url-pattern>/servlet/FirstServlet.asp</url-pattern>
         <url-pattern>/servlet/FirstServlet.php</url-pattern>
         <url-pattern>/servlet/FirstServlet.jsp</url-pattern>
         <url-pattern>/servlet/FirstServlet.aspx</url-pattern>
     </servlet-mapping>
         <servlet-mapping>
         <servlet-name>RequestServlet</servlet-name>
         <url-pattern>/servlet/RequestServlet</url-pattern>
     </servlet-mapping>
       <servlet-mapping>
     <servlet-name>IdentityServlet</servlet-name>
     <url-pattern>/servlet/IdentityServlet</url-pattern>
   </servlet-mapping>

 </web-app>

web.xml