Java EE登陆界面生成随机数防止恶意注册或者登录

package cn.com;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

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

public class ResponseDemoRandom extends HttpServlet {
	private static final long serialVersionUID = 1L;
	public static final int WIDTH=120;
	public static final int HEIGHT=25;
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		BufferedImage image=new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);
		Graphics g=image.getGraphics();
		//设置背景色
		setBackGround(g);

		//设置边框
		setBorder(g);

		//画干扰线
		drawRandomLine(g);

		//写随机数
		drawRandomNum((Graphics2D)g);

		response.setContentType("image/jpeg");
		response.setDateHeader("expries", -1);
		response.setHeader("Cache-Control", "no-control");
		response.setHeader("prama", "no-control");
		ImageIO.write(image, "jpg", response.getOutputStream());
	}

	private void drawRandomNum(Graphics2D g) {
		g.setColor(Color.PINK);
		g.setFont(new Font("宋体",Font.BOLD,20));
		int x=10;
		for(int i=0;i<4;i++)
		{
			int degree=new Random().nextInt()%30;
			int num=new Random().nextInt(9);
			String str=num+"";
			g.rotate(degree*Math.PI/180, x, 20);
			g.drawString(str, x, 20);
			g.rotate(-degree*Math.PI/180, x, 20);
			x+=30;
		}

	}

	private void drawRandomLine(Graphics g) {
		g.setColor(Color.blue);
		for(int i=0;i<5;i++)
		{
			int x1=new Random().nextInt(WIDTH-4)+2;
			int y1=new Random().nextInt(HEIGHT-4)+2;

			int x2=new Random().nextInt(WIDTH-2);
			int y2=new Random().nextInt(HEIGHT-2);

			g.drawLine(x1, y1, x2, y2);

		}

	}

	private void setBorder(Graphics g) {
		g.setColor(Color.GREEN);
		g.drawRect(1, 1, WIDTH-2, HEIGHT-2);
	}

	private void setBackGround(Graphics g) {
		g.setColor(Color.gray);
		g.fillRect(0, 0, WIDTH, HEIGHT);
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doGet(request,response);
	}

}