1.java代码如下:

package com.ask.session;
 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;
 
 /**
 * 输出一张随机图片 看jdk api 的bufferedImage类
 */

public class Demo4 extends HttpServlet {
 public static final int WIDTH=120;
 public static final int HEIGHT=30;
 @Override
 protected void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
 //构建一张图
 BufferedImage image=new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
 //创建图形上下文
 Graphics g=image.getGraphics();
 //设置背景色
 setBackgroundColor(g);
 //设置边框
 //       setBorder(g);
 //画干扰线
 drawRandomLine(g);
 //写随机数
 drawRandomNumber((Graphics2D)g);
 //图形输出到浏览器
 res.setContentType("image/jpeg");
 ImageIO.write(image, "jpg", res.getOutputStream());
 }

private void drawRandomNumber(Graphics2D g) {
 //汉字区间：\u4100~\u9fa5
 String base="1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
 String number="";
 g.setColor(Color.BLUE);
 g.setFont(new Font("宋体", Font.BOLD,25));
 int x=10;
 for (int i = 0; i < 4; i++) {
 //定义的旋转弧度30到-30的角度
 int degree=new Random().nextInt()%30;
 number=base.charAt(new Random().nextInt(base.length()))+"";
 //让字体旋转30度
 g.rotate(degree*Math.PI/180, x, 20);
 g.drawString(number, x, 23);
 //清楚旋转度数
 g.rotate(-degree*Math.PI/180, x,20);
 x+=30;
 }
 }

private void drawRandomLine(Graphics g) {
 g.setColor(Color.gray);
 for (int i = 0; i < 8; 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 setBackgroundColor(Graphics g) {
 g.setColor(Color.white);
 g.fillRect(0, 0, WIDTH, HEIGHT);
 }
 }

2.web.xml配置文件如下：

<!--随机验证码 -->
 <servlet>
 <servlet-name>demo4</servlet-name>
 <servlet-class>com.ask.session.Demo4</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>demo4</servlet-name>
 <url-pattern>/demo4</url-pattern>
 </servlet-mapping>