关于java 图形验证码的解决方法

package cn.response;

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;

@suppresswarnings("serial")
public class validatepicture extends httpservlet {

 public void doget(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  try {
   validateimage(request, response);
  } catch (exception e) {
   e.printstacktrace();
  }
 }

 public void dopost(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  doget(request, response);
 }

 public static final int width = 120;
 public static final int height = 25;

 public void validateimage(httpservletrequest request,
   httpservletresponse response) throws exception {

  bufferedimage bi = new bufferedimage(width, height,
    bufferedimage.type_int_rgb);// 在内存中构建一幅图象
  graphics g = bi.getgraphics();

  setbackground(g);// 设置背景色
  setborder(g);// 设置边框
  drawrandomline(g);// 画干扰线
  string random = drawrandomnum((graphics2d) g);// 写随机数

  request.getsession().setattribute("random", random);
  //request.getsession(false);
  response.setcontenttype("image/jpeg");
  // 设置不要缓存
  response.setdateheader("expries", -1);
  response.setheader("cache-control", "no-cache");

  imageio.write(bi, "jpg", response.getoutputstream());
 }

 private string drawrandomnum(graphics2d g) {
  g.setcolor(color.red);
  g.setfont(new font("宋体", font.bold, 20));
  // [\u4e00-\u9fa5]中文数字区间
  string base = "\u4e00\u4f00\u5e00\u4e50\u4e89\u4f10\u4e09";

  stringbuffer sb = new stringbuffer();

  int x = 5;
  for (int i = 0; i < 4; i++) {
   int degree = new random().nextint() % 30;

   string ch = base.charat(new random().nextint(base.length())) + "";
   sb.append(ch);
   g.rotate(degree * math.pi / 180, x, 20);
   g.drawstring(ch, x, 20);
   g.rotate(-degree * math.pi / 180, x, 20);

   x = x + 30;
  }
  system.out.println(sb.tostring());
  return sb.tostring();
 }

 private void drawrandomline(graphics g) {
  g.setcolor(color.green);
  for (int i = 0; i < 3; i++) {
   int x1 = new random().nextint(width);
   int y1 = new random().nextint(height);

   int x2 = new random().nextint(width);
   int y2 = new random().nextint(height);

   g.drawline(x1, y1, x2, y2);
  }
 }

 private void setborder(graphics g) {
  g.setcolor(color.blue);
  g.drawrect(1, 1, width - 2, height - 2);
 }

 private void setbackground(graphics g) {
  g.setcolor(color.white);
  g.fillrect(0, 0, width, height);
 }
}