隨即生成包含驗證碼的字符串

package com.file.test.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.OutputStream;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.apache.commons.lang.RandomStringUtils;
public class RandomImageServlet extends HttpServlet  {
	//隨即生成包含驗證碼的字符串   

	public static String random() {
	        //20060320 add by wyx
	        //因爲o和0,l和1很難區分,所以,去掉大小寫的o和l

	        String str = "";
	        str = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijkmnpqrstuvwxyz";//初始化種子
	        return RandomStringUtils.random(4, str);//返回6爲的字符串
	            }

	    /**
	     * 根據要求的數字生成圖片,背景爲白色,字體大小16,字體顏色黑色粗體
	     * @param num 要生成的數字
	     * @param out 輸出流
	     * @throws IOException
	     */
	    public static void render(String num, OutputStream out) throws IOException {
	        if (num.getBytes().length > 6) {
	            throw new IllegalArgumentException(
	                    "The length of param num cannot exceed 6.");
	        }
	        //設定寬度和高度
	        int width = 100; 

	        int height = 30; 
	        // 在內存中創建圖象
	        BufferedImage bi = new BufferedImage(width, height,
	                                             BufferedImage.TYPE_INT_RGB);
	        // 獲取圖形上下文
	        Graphics2D g = (Graphics2D) bi.getGraphics();
	        //畫邊框
	        java.util.Random random = new java.util.Random();
	        g.setColor(Color.white);
	        g.fillRect(0, 0, width, height);
	        //設置字體
	        Font mFont = new Font("Tahoma", Font.BOLD, 16);
	        g.setFont(mFont);
	        g.setColor(Color.BLACK);//設置字體顏色
	        //畫認證碼,每個認證碼在不同的水平位置
	        String str1[] = new String[4];
	        for (int i = 0; i < str1.length; i++) {
	            str1[i] = num.substring(i, i + 1);
	            int w = 0;
	            int x = (i + 1) % 3;

	//隨即生成驗證碼字符的水平偏移量
	            if (x == random.nextInt(3)) {
	                w = 19 - random.nextInt(7);
	            } else {
	                w = 19 + random.nextInt(7);
	            }

	//隨即生成顏色
	            Color color1 = new Color(random.nextInt(180), random.nextInt(180),
	                                     random.nextInt(180));
	            g.setColor(color1);
	            g.drawString(str1[i], 20 * i + 10, w);
	        }

	        // 隨機產生干擾點,並用不同的顏色表示，使圖象中的認證碼不易被其它程序探測到
	        for (int i = 0; i < 100; i++) {
	            int x = random.nextInt(width);
	            int y = random.nextInt(height);
	            Color color1 = new Color(random.nextInt(255), random.nextInt(255),
	                                     random.nextInt(255));
	            g.setColor(color1); //隨即畫各種顏色的點
	            g.drawOval(x, y, 0, 0);
	        }
	        //畫干擾線
	        for (int i = 0; i < 5; i++) {
	            int x = random.nextInt(width);
	            int y = random.nextInt(height);
	            int x1 = random.nextInt(width);
	            int y1 = random.nextInt(height);
	            Color color1 = new Color(random.nextInt(255), random.nextInt(255),
	                                     random.nextInt(255));

	            g.setColor(color1); //隨即畫各種顏色的線
	            g.drawLine(x, y, x1, y1);
	        }
	        //圖像生效
	        g.dispose();
	        //輸出頁面
	        ImageIO.write(bi, "jpg", out);
	    }
	
	    public final static String RANDOM_LOGIN_KEY = "RANDOM_LOGIN_KEY";

	    public void init() throws ServletException {
	     System.setProperty("java.awt.headless","true");
	    }

	       public static String getRandomLoginKey(HttpServletRequest req) {
	           return (String)req.getSession().getAttribute(RANDOM_LOGIN_KEY);
	       }

	       protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException
	       {
	           HttpSession ssn = req.getSession();
	           if(ssn!=null) {
	               String randomString = random();//生成種子
	               ssn.setAttribute(RANDOM_LOGIN_KEY,randomString);//將種子放到session裏面
	               res.setContentType("image/jpeg");//設置圖像生成格式
	            render(randomString,res.getOutputStream());//輸出到頁面
	           }
	       }
	       
}