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());
    }
}

<?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>