jsp/servlet生成验证码图片

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

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

public class ImageServlet extends HttpServlet {
/**
*
*/
private static final long serialVersionUID = -2792546249653301684L;

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException {
BufferedImage bi = new BufferedImage(68, 22, BufferedImage.TYPE_INT_RGB);
Graphics g = bi.getGraphics();
Color c = new Color(200, 150, 255);
g.setColor(c);
g.fillRect(0, 0, 68, 22);

char[] ch = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".toCharArray();
Random r = new Random();
int len = ch.length, index;
StringBuffer sb = new StringBuffer();
for (int i = 0; i < 4; i++) {
index = r.nextInt(len);
g.setColor(new Color(r.nextInt(88), r.nextInt(188), r.nextInt(255)));
g.drawString(ch[index] + "", (i * 15) + 3, 18);
sb.append(ch[index]);
}
request.getSession().setAttribute("piccode", sb.toString());
ImageIO.write(bi, "JPG", response.getOutputStream());
}

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

}

function changeImg(){
var imgUrl = "<%=request.getContextPath()%>/eservice/basic/auth/login/image.jsp?t="+new Date();
$("#imgId").attr('src',imgUrl);
}