通过Servlet的response绘制页面验证码

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

public class IdentityServlet extends HttpServlet {
    //不包括0，O，1，I等难以辨认的字符
    public static final char[] CHARS={'2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','I','J','K','L','M','N','P','Q','R','S','T','U','V','W','X','Y','Z'};
    
    public static Random random=new Random();
    //获取随机码
    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();
    }
    //获取随机颜色
    public static Color getRandomColor(){
        return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255));
    }
    //获取所给颜色的相反值
    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");//设置输出类型
        String randomString=getRandomString();//获取随机数
        request.getSession(true).setAttribute("randomString", randomString);//将随机数放入session中
        int width=100;//图片宽度
        int height=30;//图片高度
        
        Color color=getRandomColor();//获取颜色，用于背景色
        Color reverse=getReverseColor(color);//发色，用于前背景
        
        BufferedImage bi=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);//创建一个彩色图片
        
        Graphics2D g=bi.createGraphics();//获取绘图对象
        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);//设置颜色
        
        //绘制遭点
        for(int i=0, n=random.nextInt(50);i){
            g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);
        }
        ServletOutputStream out=response.getOutputStream();
        JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);
        encoder.encode(bi);
        out.flush();
        
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

    }
    
}

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">
  <display-name>display-name>
  
  <servlet>
    <servlet-name>IdentityServletservlet-name>
    <servlet-class>com.servlet.IdentityServletservlet-class>
  servlet>

    <servlet-name>IdentityServletservlet-name>
    <url-pattern>/servlet/IdentityServleturl-pattern>
  servlet-mapping>    
  <welcome-file-list>
    <welcome-file>index.jspwelcome-file>
  welcome-file-list>
web-app>