转:解决在验证码中的：getOutputStream() has already been called for this response异常错误

最新推荐文章于 2020-01-07 23:54:03 发布

原创最新推荐文章于 2020-01-07 23:54:03 发布 · 722 阅读

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#random #import #image

本文介绍了一个使用JSP生成随机验证码图片的方法。通过定义颜色、设置响应头、绘制背景与线条，并生成随机数字作为验证码内容，最终将图片以JPEG格式输出。此示例适用于网站登录验证等场景。

<%@ page contentType="image/jpeg"
    import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"%>
<%!Color getRandColor(int fc, int bc) {
        Random random = new Random();
        if (fc > 255)
            fc = 255;
        if (bc > 255)
            bc = 255;
        int r = fc + random.nextInt(bc - fc);
        int g = fc + random.nextInt(bc - fc);
        int b = fc + random.nextInt(bc - fc);
        return new Color(r, g, b);
    }%>
<%
    out.clear();
    response.setHeader("Pragma", "No-cache");
    response.setHeader("Cache-Control", "no-cache");
    response.setDateHeader("Expires", 0);

    int width = 60, height = 20;
    BufferedImage image = new BufferedImage(width, height,
            BufferedImage.TYPE_INT_RGB);

    Graphics g = image.getGraphics();

    Random random = new Random();

    g.setColor(getRandColor(200, 250));
    g.fillRect(0, 0, width, height);

    g.setFont(new Font("Times New Roman", Font.PLAIN, 18));

    g.setColor(getRandColor(160, 200));
    for (int i = 0; i < 155; i++) {
        int x = random.nextInt(width);
        int y = random.nextInt(height);
        int xl = random.nextInt(12);
        int yl = random.nextInt(12);
        g.drawLine(x, y, x + xl, y + yl);
    }

    String sRand = "";
    for (int i = 0; i < 4; i++) {
        String rand = String.valueOf(random.nextInt(10));
        sRand += rand;

        g.setColor(new Color(20 + random.nextInt(110), 20 + random
        .nextInt(110), 20 + random.nextInt(110)));
        g.drawString(rand, 13 * i + 6, 16);
    }

    session.setAttribute("rand", sRand);

    g.dispose();

    ImageIO.write(image, "JPEG", response.getOutputStream());
    out.clear();
    out = pageContext.pushBody();
%>