后台生成验证码图片，并将BufferedImage对象转成base64码响应为json数据

生成验证码工具类

package com.neusiri.util;
/**
* @author zdj
* @create 2018/12/19/019 18:18
* @desc 验证码
**/
import sun.misc.BASE64Encoder;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;

import java.io.*;
import java.util.Random;

public class ImageUtil {

    // 验证码字符集
    private static final char[] chars = { 
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 
        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
        'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 
        'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};
    // 字符数量
    private static final int SIZE = 4;
    // 干扰线数量
    private static final int LINES = 5;
    // 宽度
    private static final int WIDTH = 80;
    // 高度
    private static final int HEIGHT = 30;
    // 字体大小
    private static final int FONT_SIZE = 30;

    /**
     * 生成随机验证码及图片
     * Object[0]：验证码字符串；
     * Object[1]：验证码图片。
     */
    public static Object[] createImage() {
        StringBuffer sb = new StringBuffer();
        // 1.创建空白图片
        BufferedImage image = new BufferedImage(
            WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
        // 2.获取图片画笔
        Graphics graphic = image.getGraphics();
        // 3.设置画笔颜色
        graphic.setColor(Color.LIGHT_GRAY);
        // 4.绘制矩形背景
        graphic.fillRect(0, 0, WIDTH, HEIGHT);
        // 5.画随机字符
        Random ran = new Random();
        for (int i = 0; i <SIZE; i++) {
            // 取随机字符索引
            int n = ran.nextInt(chars.length);
            // 设置随机颜色
            graphic.setColor(getRandomColor());
            // 设置字体大小
            graphic.setFont(new Font(
                null, Font.BOLD + Font.ITALIC, FONT_SIZE));
            // 画字符
            graphic.drawString(
                chars[n] + "", i * WIDTH / SIZE, HEIGHT*2/3);
            // 记录字符
            sb.append(chars[n]);
        }
        // 6.画干扰线
        for (int i = 0; i < LINES; i++) {
            // 设置随机颜色
            graphic.setColor(getRandomColor());
            // 随机画线
            graphic.drawLine(ran.nextInt(WIDTH), ran.nextInt(HEIGHT),
                    ran.nextInt(WIDTH), ran.nextInt(HEIGHT));
        }
        // 7.返回验证码和图片
        return new Object[]{sb.toString(), image};
    }

    /**
     * 随机取色
     */
    public static Color getRandomColor() {
        Random ran = new Random();
        Color color = new Color(ran.nextInt(256), 
                ran.nextInt(256), ran.nextInt(256));
        return color;
    }
    
    public static void main(String[] args) throws IOException {
        Object[] objs = createImage();
        BufferedImage image = (BufferedImage) objs[1];
        OutputStream os = new FileOutputStream("D:/1.png");
        ImageIO.write(image, "png", os);
        os.close();

    }
}

验证码接口Controller

package com.neusiri.epcstest.login.controller;

import com.neusiri.util.ImageUtil;
import com.neusiri.util.JsonRESTResult;
import com.neusiri.util.JsonRESTResultMsg;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import sun.misc.BASE64Encoder;

import javax.imageio.ImageIO;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.util.HashMap;
import java.util.Map;


@RestController
public class ValidateCodeController {
    /**
     * @author zdj
     * @create 2018/12/19/019 18:23
     * @desc 利用验证码工具生成验证码
     **/
/*    @RequestMapping(value = "/validateCode")
    public JsonRESTResult validate(HttpSession session, HttpServletRequest request,
                                   HttpServletResponse response)throws Exception{
        JsonRESTResult jsonRESTResult = new JsonRESTResult();
        //利用图片工具生成图片
        //第一个参数是生成的验证码，第二个参数是生成的图片
        Object[] objs = ImageUtil.createImage();
        //将验证码存入Session
        session.setAttribute("imageCode",objs[0]);
        System.out.println("验证码："+session.getAttribute("imageCode"));
        //将图片输出给浏览器
        BufferedImage image = (BufferedImage) objs[1];
        response.setContentType("image/png");
        OutputStream os = response.getOutputStream();
        ImageIO.write(image, "png", os);
        jsonRESTResult.setCode(JsonRESTResultMsg.CODE_800.getCode());
        jsonRESTResult.setMsg("生成验证码成功");
        jsonRESTResult.setData(objs[0]);
        return jsonRESTResult;
    }   */
    @RequestMapping(value = "/validateCode")
    public JsonRESTResult validate(HttpSession session, HttpServletRequest request,
                                   HttpServletResponse response)throws Exception{
        JsonRESTResult jsonRESTResult = new JsonRESTResult();
        //利用图片工具生成图片
        //第一个参数是生成的验证码，第二个参数是生成的图片
        Object[] objs = ImageUtil.createImage();
        //将验证码存入Session
        session.setAttribute("imageCode",objs[0]);
//        System.out.println("验证码："+session.getAttribute("imageCode"));


        //将图片转正base64
        BufferedImage image = (BufferedImage) objs[1];
        //转base64
        BASE64Encoder encoder = new BASE64Encoder();
        ByteArrayOutputStream baos = new ByteArrayOutputStream();//io流
        ImageIO.write(image, "png", baos);//写入流中
        byte[] bytes = baos.toByteArray();//转换成字节
        String png_base64 =  encoder.encodeBuffer(bytes).trim();//转换成base64串
        //删除 \r\n
        png_base64 = png_base64.replaceAll("\n", "").replaceAll("\r", "");

        Map map = new HashMap<>();
        map.put("base64","data:image/png;base64,"+ png_base64);
        map.put("validateCode",objs[0]);

        jsonRESTResult.setCode(JsonRESTResultMsg.CODE_800.getCode());
        jsonRESTResult.setMsg("生成验证码成功");
        jsonRESTResult.setData(map);
        return jsonRESTResult;
    }
}

注：转换成base64串时，一定要删除\r和\n

线上测试工具：图片和base64串项目转换http://imgbase64.duoshitong.com/