Java: how to send POST request while displaying the page?

Here is my code:

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(),
开发者_StackOverflow                "/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);
        }

By the time I use showDocument, the POST request is already done, so what I'm really doing is showing a blank page (instead, I want to show the image). The source of image.php is this:

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

You are using POST on Java and GET on PHP...

Your showDocument and the applet's POST request are completely independent. The POST request is done by your applet, and the result would be only usable inside your applet (but you are not reading it at all - and I'm not sure it is even sent).

showDocument, in contrast, always does a GET request - there is no way to instruct the browser to use POST here. You might be able to fabricate a POST request for a new HTML page by using the JavaScript bridge from your applet, though.

Theoretically, it should work anyways, as you send the image data as part of the URL, too, but there might be a length limit for the URL data in the Web server, or in the link from Java-Plugin to the browser.

You could instead encode your image in a data: URL, and use this for showDocument.

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

(I did not test if Java's URL class actually accepts this. Please try and report. I suppose it is subject to the same browser URL length limits.)

An alternative would be having the server store the image (at least for some short time). Then you would use your POST from the applet to upload the data, get back (short) some unique identifier, which you then would pass to the showDocument URL.