java原生动态生成验证码

package lhw.wanlin.checkimg;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

@WebServlet(name = "CheckServlet")
public class CheckServlet extends HttpServlet {
 //集中保存所有成语
 private List<String> words = new ArrayList<>();

 @Override
 public void init() throws ServletException {
  // 初始化阶段，读取new_words.txt
  // web工程中读取 文件，必须使用绝对磁盘路径
  String path = getServletContext().getRealPath("/WEB-INF/new_words.txt");
  try {
   BufferedReader br = new BufferedReader(new FileReader(path));
   String line;
   while ((line = br.readLine()) != null){
    words.add(line);
   }
   br.close();
  } catch (FileNotFoundException e) {
   e.printStackTrace();
  } catch (IOException e) {
   e.printStackTrace();
  }
 }

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

 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // 禁止缓存
  // response.setHeader("Cache-Control", "no-cache");
  // response.setHeader("Pragma", "no-cache");
  // response.setDateHeader("Expires", -1);
  System.out.println(words);

  int width = 120;
  int height = 30;

  // 步骤一 绘制一张内存中图片
  BufferedImage bufferedImage = new BufferedImage(width, height,
    BufferedImage.TYPE_INT_RGB);

  // 步骤二 图片绘制背景颜色 ---通过绘图对象
  Graphics graphics = bufferedImage.getGraphics();// 得到画图对象 --- 画笔
  // 绘制任何图形之前 都必须指定一个颜色
  graphics.setColor(getRandColor(200, 250));
  graphics.fillRect(0, 0, width, height);

  // 步骤三 绘制边框
  graphics.setColor(Color.WHITE);
  graphics.drawRect(0, 0, width - 1, height - 1);

  // 步骤四 四个随机数字
  Graphics2D graphics2d = (Graphics2D) graphics;
  // 设置输出字体
  graphics2d.setFont(new Font("宋体", Font.BOLD, 18));

  Random random = new Random();// 生成随机数
  int index = random.nextInt(words.size());
  String word = words.get(index);// 获得成语

  // 定义x坐标
  int x = 10;
  for (int i = 0; i < word.length(); i++) {
   // 随机颜色
   graphics2d.setColor(new Color(20 + random.nextInt(110), 20 + random
     .nextInt(110), 20 + random.nextInt(110)));
   // 旋转 -30 --- 30度
   int jiaodu = random.nextInt(60) - 30;
   // 换算弧度
   double theta = jiaodu * Math.PI / 180;

   // 获得字母数字
   char c = word.charAt(i);

   // 将c 输出到图片
   graphics2d.rotate(theta, x, 20);
   graphics2d.drawString(String.valueOf(c), x, 20);
   graphics2d.rotate(-theta, x, 20);
   x += 30;
  }

  // 将验证码内容保存session
  request.getSession().setAttribute("checkcode_session", word);

  // 步骤五 绘制干扰线
  graphics.setColor(getRandColor(160, 200));
  int x1;
  int x2;
  int y1;
  int y2;
  for (int i = 0; i < 30; i++) {
   x1 = random.nextInt(width);
   x2 = random.nextInt(12);
   y1 = random.nextInt(height);
   y2 = random.nextInt(12);
   graphics.drawLine(x1, y1, x1 + x2, x2 + y2);
  }

  // 将上面图片输出到浏览器 ImageIO
  graphics.dispose();// 释放资源

  //将图片写到response.getOutputStream()中
  ImageIO.write(bufferedImage, "jpg", response.getOutputStream());
 }

 /**
  * 取其某一范围的color
  *
  * @param fc
  *   int 范围参数1
  * @param bc
  *   int 范围参数2
  * @return Color
  */
 private Color getRandColor(int fc, int bc) {
  // 取其随机颜色
  Random random = new Random();
  if (fc > 255) {
   fc = 255;
  }
  if (bc > 255) {
   bc = 255;
  }
  int r = fc + random.nextInt(bc - fc);
  int g = fc + random.nextInt(bc - fc);
  int b = fc + random.nextInt(bc - fc);
  return new Color(r, g, b);
 }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
   version="4.0">
 <servlet>
  <servlet-name>CheckServlet</servlet-name>
  <servlet-class>lhw.wanlin.checkimg.CheckServlet</servlet-class>
 </servlet>
 <servlet-mapping>
  <servlet-name>CheckServlet</servlet-name>
  <url-pattern>/checkServlet</url-pattern>
 </servlet-mapping>
</web-app>