Java:如何在显示页面时发送POST请求

下面是我的代码:

try
        {
            ByteArrayOutputStream os = new ByteArrayOutputStream();
            ImageIO.write(image, "png", os);
            byte[] bytes = os.toByteArray();
            os.flush();
            os.close();
            String code = encode(bytes);
            URL base = applet.getCodeBase();
            URL url = new URL(base.getProtocol(),
                base.getHost(),
                base.getPort(),
                "/image.php?code=" + code);

            HttpURLConnection c = (HttpURLConnection) url.openConnection();
            c.setRequestMethod("POST");
            c.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            c.setDoOutput(true);
            DataOutputStream s = new DataOutputStream(c.getOutputStream());
            s.writeBytes("code=" + code);
            applet.getAppletContext().showDocument(url, "_blank");
        }
        catch (Exception e)
        {
            e.printStackTrace();
            JOptionPane.showMessageDialog(
                this,
                e.toString(),
                "Error",
                JOptionPane.ERROR_MESSAGE);
        }

当我使用showDocument时，POST请求已经完成，所以我真正要做的是显示一个空白页面(相反，我想显示图像)。image.php的源代码如下:

<?php
$code = base64_decode($_GET["code"]);
header('Content-Type: image/png');
echo $code;
?>

URL url = new URL("data:image/png;base64," + code);