实现登录验证码

1、ValidateCode.java

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

import javax.imageio.ImageIO;
import javax.servlet.ServletException;

import org.springframework.stereotype.Service;


/**
 * 登录验证码
 *
 */
public class ValidateCode  {
    
    /**
     * 得到验证码图片
     * @param out
     * @param number 验证数字
     * @throws ServletException
     * @throws IOException
     */
    public void getImage(OutputStream out,String number)
            throws ServletException, IOException {
        //0.创建空白图片
        BufferedImage image=new BufferedImage(100,30,BufferedImage.TYPE_INT_RGB);
        //1.获取图片画笔
        Graphics g = image.getGraphics();
        Random r=new Random();
        //2.设置画笔颜色(Random类中的nextInt(n)返回一个大于等于0，小于n的随机数)
        g.setColor(new Color(r.nextInt(255),r.nextInt(255), r.nextInt(255)));
        //3.绘制矩形的背景
        g.fillRect(0, 0, 100, 30);
        //4.调用自定义的方法，获取长度为4的字母数字组合的字符串
        g.setColor(new Color(0,0,0));
        g.setFont(new Font(null,Font.BOLD,24));
        //5.设置颜色字体后，绘制字符串（x/y,最左边字符所处的位置）
        g.drawString(number, 20, 24);
        //6.绘制8条干扰线(alpha表示透明度)
        for(int i=0;i<8;i++){
            g.setColor(new Color(r.nextInt(255),r.nextInt(255), r.nextInt(255),r.nextInt(255)));
            g.drawLine(r.nextInt(100), r.nextInt(30), r.nextInt(100), r.nextInt(30));
        }
        ImageIO.write(image, "jpeg", out);
    }
    
    //自定义方法，获取长度为size的字母数字组合的字符串
    public String getNumber(int size){
        String str="ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        String number="";
        Random r = new Random();
        for(int i=0;i<size;i++){
            number+=str.charAt(r.nextInt(str.length()));
        }
        return number;
    }

}

2、Controller

    @RequestMapping(value = "/check",method={RequestMethod.GET})
    @ResponseBody
    public void check(HttpServletRequest req) {
        try {
            HttpServletResponse response = this.getResponse();
            response.setContentType("application/octet-stream");
            response.addHeader("Content-Disposition", "attachment;filename=" + "vcode.jpeg");
            String number = validateCode.getNumber(4);
            validateCode.getImage(response.getOutputStream(),number);
        } catch (Exception e) {
            
        }
    }

3、html

<img style="width:4.4rem;height:1.9rem; margin-left:0.8rem;" src="http://127.0.0.1:8080/test/check">

效果图