java springboot 实现图片下载功能

生成验证码：
提供一个接口， 这个接口里，我们将生成的验证码存入session，然后将验证码以图片格式或者base64编码串返回给调用端。

校验验证码：
提供一个接口，这个接口里，我们收到调用端传过来的校验码，然后从session取出验证码，两个验证码都全部转小写，进行无大小写区分匹配校验，返回true/flase 。

存储验证码：
生成的验证码，在未生成图片的时候，就将4位验证码字符先存入session，以‘JCCODE’作为存取session的key。

创建工具类：

import javax.imageio.ImageIO;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.util.Base64;
import java.util.Random;
 

public class ValidateCodeUtil {
 
 
    private static Random random = new Random();
    private int width = 165; //验证码的宽
    private int height = 45; //验证码的高
    private int lineSize = 30; //验证码中夹杂的干扰线数量
    private int randomStrNum = 4; //验证码字符个数
 
    private String randomString = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWSYZ";
    private final String sessionKey = "JCCODE";
 
    //字体的设置
    private Font getFont() {
        return new Font("Times New Roman", Font.ROMAN_BASELINE, 40);
    }
 
    //颜色的设置
    private static Color getRandomColor(int fc, int bc) {
 
        fc = Math.min(fc, 255);
        bc = Math.min(bc, 255);
 
        int r = fc + random.nextInt(bc - fc - 16);
        int g = fc + random.nextInt(bc - fc - 14);
        int b = fc + random.nextInt(bc - fc - 12);
 
        return new Color(r, g, b);
    }
 
    //干扰线的绘制
    private void drawLine(Graphics g) {
        int x = random.nextInt(width);
        int y = random.nextInt(height);
        int xl = random.nextInt(20);
        int yl = random.nextInt(10);
        g.drawLine(x, y, x + xl, y + yl);
 
    }
 
    //随机字符的获取
    private  String getRandomString(int num){
        num = num > 0 ? num : randomString.length();
        return String.valueOf(randomString.charAt(random.nextInt(num)));
    }
 
    //字符串的绘制
    private String drawString(Graphics g, String randomStr, int i) {
        g.setFont(getFont());
        g.setColor(getRandomColor(108, 190));
        //System.out.println(random.nextInt(randomString.length()));
        String rand = getRandomString(random.nextInt(randomString.length()));
        randomStr += rand;
        g.translate(random.nextInt(3), random.nextInt(6));
        g.drawString(rand, 40 * i + 10, 25);
        return randomStr;
    }
 
 
    //生成随机图片
    public void getRandomCodeImage(HttpServletRequest request, HttpServletResponse response){
        HttpSession session = request.getSession();
        // BufferedImage类是具有缓冲区的Image类,Image类是用于描述图像信息的类
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
        Graphics g = image.getGraphics();
        g.fillRect(0, 0, width, height);
        g.setColor(getRandomColor(105, 189));
        g.setFont(getFont());
        // 干扰线
        for (int i = 0; i < lineSize; i++) {
            drawLine(g);
        }
        // 随机字符
        String randomStr = "";
        for (int i = 0; i < randomStrNum; i++) {
            randomStr = drawString(g, randomStr, i);
        }
        System.out.println("随机字符："+randomStr);
        g.dispose();
        //移除之前的session中的验证码信息
        session.removeAttribute(sessionKey);
        //重新将验证码放入session
        session.setAttribute(sessionKey, randomStr);
        try {
            //  将图片以png格式返回,返回的是图片
            ImageIO.write(image, "PNG", response.getOutputStream());
 
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
 
 
 
 
     //生成随机图片的base64编码字符串
 
    public String getRandomCodeBase64(HttpServletRequest request, HttpServletResponse response) {
        HttpSession session = request.getSession();
        // BufferedImage类是具有缓冲区的Image类,Image类是用于描述图像信息的类
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
        Graphics g = image.getGraphics();
        g.fillRect(0, 0, width, height);
        g.setColor(getRandomColor(105, 189));
        g.setFont(getFont());
        //干扰线
        for (int i = 0; i < lineSize; i++) {
            drawLine(g);
        }
 
        //随机字符
        String randomStr = "";
        for (int i = 0; i < randomStrNum; i++) {
            randomStr = drawString(g, randomStr, i);
        }
        System.out.println("随机字符："+randomStr);
        g.dispose();
        session.removeAttribute(sessionKey);
        session.setAttribute(sessionKey, randomStr);
        String base64String = "";
        try {
            //  直接返回图片
            //  ImageIO.write(image, "PNG", response.getOutputStream());
            //返回 base64
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            ImageIO.write(image, "PNG", bos);
 
            byte[] bytes = bos.toByteArray();
            Base64.Encoder encoder = Base64.getEncoder();
            base64String = encoder.encodeToString(bytes);
 
        } catch (Exception e) {
            e.printStackTrace();
        }
 
        return base64String;
    }
 
 
 
    }

接下来写接口，创建一个ValidateCodeController.java，
先是生成验证码，返回图片的接口：

import com.example.demo.util.ValidateCodeUtil;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
 
/**
 * @Author : JCccc
 * @CreateTime : 2019/9/25
 * @Description :
 **/
 
@RestController
public class ValidateCodeController {
 
 
    //返回验证码图片
   @GetMapping("/getCaptchaImg")
   public void getCaptchaImg(HttpServletRequest request, HttpServletResponse response, HttpSession session) {
 
       try {
 
           response.setContentType("image/png");
           response.setHeader("Cache-Control", "no-cache");
           response.setHeader("Expire", "0");
           response.setHeader("Pragma", "no-cache");
           ValidateCodeUtil validateCode = new ValidateCodeUtil();
           // getRandomCodeImage方法会直接将生成的验证码图片写入response
           validateCode.getRandomCodeImage(request, response);
           // System.out.println("session里面存储的验证码为："+session.getAttribute("JCCODE"));
 
       } catch (Exception e) {
           e.printStackTrace();
       }
 
   }
 
 
}

用postman来调用下接口：

可以看到控制台的打印，这个验证码字符串已经存入了session

接下来是编写一个校验验证码接口：

//验证码校验
    @GetMapping("/checkCaptcha")
    public boolean getCheckCaptcha(@RequestParam("code") String code, HttpSession session) {
 
        try {
            //toLowerCase() 不区分大小写进行验证码校验
            String sessionCode= String.valueOf(session.getAttribute("JCCODE")).toLowerCase();
            System.out.println("session里的验证码："+sessionCode);
            String receivedCode=code.toLowerCase();
            System.out.println("用户的验证码："+receivedCode);
            return !sessionCode.equals("") && !receivedCode.equals("") && sessionCode.equals(receivedCode);
 
        } catch (Exception e) {
 
            return false;
        }
 
    }

用postman调下接口，先生成验证码模拟返回给页面了

然后调用校验验证码接口，模拟用户在页面输入验证码，

可以看到校验正确。

 

返回base64编码串的接口

// 生成验证码,返回的是 base64
    @GetMapping("/getCaptchaBase64")
    public Object getCaptchaBase64(HttpServletRequest request, HttpServletResponse response) {
 
        Map result = new HashMap();
        try {
 
            response.setContentType("image/png");
            response.setHeader("Cache-Control", "no-cache");
            response.setHeader("Expire", "0");
            response.setHeader("Pragma", "no-cache");
            ValidateCodeUtil validateCode = new ValidateCodeUtil();
            // 返回base64
            String base64String = validateCode.getRandomCodeBase64(request, response);
            result.put("url", "data:image/png;base64," + base64String);
            result.put("message", "created successfull");
           //http://tool.chinaz.com/tools/imgtobase/  base64直接转为图片网站
            System.out.println("结果：" + result.get("url"));
 
        } catch (Exception e) {
            System.out.println(e);
        }
 
        return result;
    }

用postman调用一下：

控制台打印：

将url取出来：

data:image/png;base64,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

去base64编码串转图片的网站去看看，对应的验证码图：