web中向瀏覽器中輸出隨機圖片

package com.yueting.util;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.http.*;
/**
 * 這個類用於產生隨機圖片
 * @author Administrator
 *
 */
class MyRandomImage
{
	//圖片的長度和寬度
	private int width = 120;
	private int height = 30;
	private String imageName;// 用戶存放在HttpSession中的隨機字符串的變量
	
	public MyRandomImage(HttpServletResponse resp, HttpServletRequest req) throws IOException
	{
		resp.setHeader("Pragma", "-1");
		resp.setHeader("Expires", "-1");
		resp.setHeader("Cache-Control", "no-cache");
		
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
		
		Graphics g = image.getGraphics();
		//設置背景顏色
		setBackground(g);
		
		//設置邊框
		setBorder(g);
		
		//設置干擾線
		MakeRadomLine(g);
		
		//產生隨機字符
		StringBuilder sb = randomChar(g);
		
		//將圖片上產生的隨機字符存放到session中
		req.getSession().setAttribute("random", sb.toString());
		
		resp.setContentType("image/jpeg");
		ImageIO.write(image, "jpg", resp.getOutputStream());
		
	}
	/**
	 * 設置背景顏色
	 * @param g
	 */
	private void setBackground(Graphics g)
	{
		g.setColor(Color.WHITE);
		g.fillRect(0, 0, width, height);
	}
	/**
	 * 設置圖片邊框顏色
	 * @param g
	 */
	private void setBorder(Graphics g)
	{
		g.setColor(Color.blue);
		g.drawRect(0, 1, width-2, height-2);
	}
	/**
	 * 在圖片上畫干擾線
	 * @param g
	 */
	private void MakeRadomLine(Graphics g)
	{
		g.setColor(Color.GREEN);
		Color[] c = {Color.red, Color.blue, Color.BLACK, Color.gray};
		for(int i = 0; i < 4; i++)
		{
			g.setColor(c[new Random().nextInt(4)] );
			g.drawLine(new Random().nextInt(30), new Random().nextInt(30),
					new Random().nextInt(150), new Random().nextInt(30));
		}
	}
	/**
	 * 在圖片上畫字符
	 * @param g
	 * @return
	 */
	private StringBuilder randomChar(Graphics g)
	{
		StringBuilder sb = new StringBuilder();
		for(int i = 0; i < 4; i++)
		{
			String str = (char)(62+new Random().nextInt(26))+"" ;
			sb.append(str);
			g.setFont(new Font(null, Font.BOLD, 20));
			Graphics2D g2 = (Graphics2D)g;
			
			g.drawString(str, 15+i*20, 25);
			
		}
		return sb;
	}
	
}