ServletOutputStream 和图片的关系

Question

在前台页面有如下语句
<img onclick="this.src='/ran/random?random='+Math.random()" alt="验证码，点击图片更换" src="/ran/random?random=0.2868249340216069" width="86" height="40">

其中src 指向的地址不是一个img文件，而是一个转到SpringMVC的类中方法
src="/ran/random?random=0.2868249340216069"

方法如下：

@Controller
public class RandomCodeController {
    @RequestMapping(value={"/ran/random"})
    public void genericRandomCode(HttpServletRequest request, HttpServletResponse response) throws IOException {
    response.setHeader("Cache-Control", "private,no-cache,no-store");
    response.setContentType("image/png");
    HttpSession session = request.getSession();
    int width = 85;
    int height = 28;
    BufferedImage image = new BufferedImage(width, height, 2);
    Graphics2D g = image.createGraphics();
    g.setComposite(AlphaComposite.getInstance(3, 1.0f));
    Random random = new Random();
    g.setColor(new Color(231, 231, 231));
    g.fillRect(0, 0, width, height);
    g.setFont(new Font("Microsoft YaHei", 2, 24));
    String sRand = "";
    for (int responseOutputStream = 0; responseOutputStream < 4; ++responseOutputStream) {
        String rand = String.valueOf(random.nextInt(10));
        sRand = sRand + rand;
        g.setColor(new Color(121, 143, 96));
        g.drawString(rand, 13 * responseOutputStream + 16, 23);
    }
    session.setAttribute("COMMON_RAND_CODE", (Object)sRand);
    g.dispose();
    ServletOutputStream var12 = response.getOutputStream();
    ImageIO.write((RenderedImage)image, "png", (OutputStream)var12);
    var12.close();
    }
}

所以其实这个src相联系的是一个ServletOutputStream
这个地方我不太理解
ServletOutputStream如何和一个图片联系起来？

Answer 1

不仅仅是图片，其他文件也是以流的形式传输的。浏览器把后台给的流解析成了图片了。