将 Base64 编码的字节 [] 作为 JSON MIME 类型传递

Question

我有一个@Produces(MediaType.APPLICATION_JSON) 的 REST 服务。在 REST 服务中，我创建了一个 BufferedImage 类型的图像，然后将其作为 png 图像写入ImageIO。接下来，我将此图像编码为Base64 encoded 字符串。现在我需要以JSON 格式返回这个编码字符串，然后在客户端我需要在img 标记中使用Base64 字符串，如下所示：

<img id="captchaImage" src="data:image/png;base64,<%=Base64ImageString%>"/>

如何将 Base64 传递为 MediaType.APPLICATION_JSON

代码：

import java.awt.Color;
import java.awt.Font;
import java.awt.GradientPaint;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.security.GeneralSecurityException;
import java.util.Base64;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.inject.Named;
import javax.servlet.http.HttpServletRequest;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.Response.Status;

@RestService
@Named("CaptchaServlet")
@Path("/reCaptchaImg")
@Produces(MediaType.APPLICATION_JSON)
public class CaptchaServlet implements ICaptchaServlet{

    @Override
    public Response processRequest(HttpServletRequest request) throws GeneralSecurityException, IOException {
        try {
        System.out.println("shaan Inside processRequest");
        int width = 150;
        int height = 50;

        //Random string generation happens
        Random r = new Random();
        int length = 6;
        System.out.println("shaan Creating string parameter");
        StringBuffer captchaStringBuffer = new StringBuffer();
        for (int i = 0; i < length; i++) {
            int baseCharNumber = ((r.nextInt((500-1)+1)+1) % 62);
            int charNumber = 0;
            if (baseCharNumber < 26) {
              charNumber = 65 + baseCharNumber;
            }
            else if (baseCharNumber < 52){
              charNumber = 97 + (baseCharNumber - 26);
            }
            else {
              charNumber = 48 + (baseCharNumber - 52);
            }
            captchaStringBuffer.append((char)charNumber);
        }
        String captchaString = captchaStringBuffer.toString();
        System.out.println("The random string generated is : "+captchaString);

        char[] s3 = captchaString.toCharArray();
        System.out.println("shaan1");

        //Converting Captcha String to Image
        BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2d = bufferedImage.createGraphics();
        System.out.println("shaan2");
        Font font = new Font("Georgia", Font.BOLD, 18);
        g2d.setFont(font);
        System.out.println("shaan3");
        RenderingHints rh = new RenderingHints(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        System.out.println("shaan4");
        rh.put(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
        g2d.setRenderingHints(rh);
        System.out.println("shaan5");
        GradientPaint gp = new GradientPaint(0, 0, Color.red, 0, height / 2, Color.black, true);
        g2d.setPaint(gp);
        g2d.fillRect(0, 0, width, height);
        g2d.setColor(new Color(255, 153, 0));
        System.out.println("shaan6");
        String captcha = String.copyValueOf(s3);
        System.out.println("shaan7");
        int x = 0;
        int y = 0;
        for (int i = 0; i < s3.length; i++) {
            x += 10 + (Math.abs(r.nextInt()) % 15);
            y = 20 + Math.abs(r.nextInt()) % 20;
            g2d.drawChars(s3, i, 1, x, y);
        }
        g2d.dispose();
        System.out.println("shaan8");
        System.out.println("shaan9");

        //Sending Image in output
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write(bufferedImage, "png", baos);
        byte[] imageData = baos.toByteArray();
        System.out.println("shaan10" + captcha);
        request.getSession().setAttribute("captcha", captcha);
        System.out.println("shaan11");
        baos.flush();
        baos.close();
        System.out.println("shaan12");
        System.out.println("The imageData is :"+imageData);

        //Encoding to Base64
        byte[] encoded = Base64.getEncoder().encode(imageData);
        System.out.println("The encoded is :"+encoded);
        return Response.ok(encoded, MediaType.APPLICATION_JSON).build();
        }catch (IOException e) {
            // TODO Auto-generated catch block
            System.out.println("In Error Catch block");
            e.printStackTrace();
            return Response.status(Status.BAD_REQUEST).build();
        }
}

代码中的行输出仅供参考：

System.out.println("The imageData is :"+imageData);
The imageData is :[B@238bbb96

System.out.println("The encoded is :"+encoded);
The encoded is :[B@1a477e17

Answer 1

我认为您尝试做的事情行不通，对我来说也没有意义。

Data-URI 旨在将图像的数据直接包含在 HTML 中，而不是从外部 URL 链接。

您应该只返回图像而不将其编码为 Base64 并直接链接它。

您可以将代码更改为：

import java.awt.Color;
import java.awt.Font;
import java.awt.GradientPaint;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.inject.Named;
import javax.servlet.http.HttpServletRequest;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.Response.Status;

@Named("CaptchaServlet")
@Path("/reCaptchaImg")
@Produces("image/png")
public class CaptchaServlet {

    @GET
    public Response processRequest(@Context HttpServletRequest request) {
        try {
            System.out.println("shaan Inside processRequest");
            int width = 150;
            int height = 50;

            //Random string generation happens
            Random r = new Random();
            int length = 6;
            System.out.println("shaan Creating string parameter");
            StringBuffer captchaStringBuffer = new StringBuffer();
            for (int i = 0; i < length; i++) {
                int baseCharNumber = ((r.nextInt((500 - 1) + 1) + 1) % 62);
                int charNumber = 0;
                if (baseCharNumber < 26) {
                    charNumber = 65 + baseCharNumber;
                } else if (baseCharNumber < 52) {
                    charNumber = 97 + (baseCharNumber - 26);
                } else {
                    charNumber = 48 + (baseCharNumber - 52);
                }
                captchaStringBuffer.append((char) charNumber);
            }
            String captchaString = captchaStringBuffer.toString();
            System.out.println("The random string generated is : " + captchaString);

            char[] s3 = captchaString.toCharArray();
            System.out.println("shaan1");

            //Converting Captcha String to Image
            BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
            Graphics2D g2d = bufferedImage.createGraphics();
            System.out.println("shaan2");
            Font font = new Font("Georgia", Font.BOLD, 18);
            g2d.setFont(font);
            System.out.println("shaan3");
            RenderingHints rh = new RenderingHints(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            System.out.println("shaan4");
            rh.put(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
            g2d.setRenderingHints(rh);
            System.out.println("shaan5");
            GradientPaint gp = new GradientPaint(0, 0, Color.red, 0, height / 2, Color.black, true);
            g2d.setPaint(gp);
            g2d.fillRect(0, 0, width, height);
            g2d.setColor(new Color(255, 153, 0));
            System.out.println("shaan6");
            String captcha = String.copyValueOf(s3);
            System.out.println("shaan7");
            int x = 0;
            int y = 0;
            for (int i = 0; i < s3.length; i++) {
                x += 10 + (Math.abs(r.nextInt()) % 15);
                y = 20 + Math.abs(r.nextInt()) % 20;
                g2d.drawChars(s3, i, 1, x, y);
            }
            g2d.dispose();
            System.out.println("shaan8");
            System.out.println("shaan9");

            //Sending Image in output
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ImageIO.write(bufferedImage, "png", baos);
            byte[] imageData = baos.toByteArray();
            System.out.println("shaan10" + captcha);
            request.getSession(true).setAttribute("captcha", captcha);
            System.out.println("shaan11");
            baos.flush();
            baos.close();
            System.out.println("The imageData is :" + imageData);

            return Response.ok(imageData, "image/png").build();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            System.out.println("In Error Catch block");
            e.printStackTrace();
            return Response.status(Status.BAD_REQUEST).build();
        }
    }
}

然后你可以像这样使用图像：

<!DOCTYPE html>
<html>
    <body>
        <h1>Hello World!</h1>
        <img id="captchaImage" alt="muh" src="/YOUR_REST_PATH/reCaptchaImg"/>
    </body>
</html>