Since the Android developers recommend to use the HttpURLConnection
class, I was wondering if anyone can provide me with a good example on how to send a bitmap "file" (actually an in-memory stream) via POST to an Apache HTTP server. I'm not interested in cookies or authentication or anything complicated, but I just want to have a reliable and logic implementation. All the examples that I've seen around here look more like "let's try this and maybe it works".
Right now, I have this code:
URL url;
HttpURLConnection urlConnection = null;
try {
url = new URL("http://example.com/server.cgi");
urlConnection = (HttpURLConnection) url.openConnection();
} catch (Exception e) {
this.showDialog(getApplicationContext(), e.getMessage());
}
finally {
if (urlConnection != null)
{
urlConnection.disconnect();
}
}
where showDialog should just display an AlertDialog
(in case of an invalid URL?).
Now, let's say that I generate a bitmap like so: Bitmap image = this.getBitmap()
inside a control derived from View
and I want to send it via POST. What would be the proper procedure to achieve such a thing? What classes do I need to use? Can I use HttpPost
like in this example? If so, how would I construct the InputStreamEntity
for my bitmap? I would find it revolting to be required to first store the bitmap in a file on the device.
I should also mention that I really need to send every unaltered pixel of the original bitmap to the server, so I can't convert it to JPEG.
I have no idea why the HttpURLConnection
class does not provide any means to send files without having to compose the file wrapper manually. Here's what I ended up doing, but if someone knows a better solution, please let me know.
Input data:
Bitmap bitmap = myView.getBitmap();
Static stuff:
String attachmentName = "bitmap";
String attachmentFileName = "bitmap.bmp";
String crlf = "\r\n";
String twoHyphens = "--";
String boundary = "*****";
Setup the request:
HttpURLConnection httpUrlConnection = null;
URL url = new URL("http://example.com/server.cgi");
httpUrlConnection = (HttpURLConnection) url.openConnection();
httpUrlConnection.setUseCaches(false);
httpUrlConnection.setDoOutput(true);
httpUrlConnection.setRequestMethod("POST");
httpUrlConnection.setRequestProperty("Connection", "Keep-Alive");
httpUrlConnection.setRequestProperty("Cache-Control", "no-cache");
httpUrlConnection.setRequestProperty(
"Content-Type", "multipart/form-data;boundary=" + this.boundary);
Start content wrapper:
DataOutputStream request = new DataOutputStream(
httpUrlConnection.getOutputStream());
request.writeBytes(this.twoHyphens + this.boundary + this.crlf);
request.writeBytes("Content-Disposition: form-data; name=\"" +
this.attachmentName + "\";filename=\"" +
this.attachmentFileName + "\"" + this.crlf);
request.writeBytes(this.crlf);
Convert Bitmap
to ByteBuffer
:
//I want to send only 8 bit black & white bitmaps
byte[] pixels = new byte[bitmap.getWidth() * bitmap.getHeight()];
for (int i = 0; i < bitmap.getWidth(); ++i) {
for (int j = 0; j < bitmap.getHeight(); ++j) {
//we're interested only in the MSB of the first byte,
//since the other 3 bytes are identical for B&W images
pixels[i + j] = (byte) ((bitmap.getPixel(i, j) & 0x80) >> 7);
}
}
request.write(pixels);
End content wrapper:
request.writeBytes(this.crlf);
request.writeBytes(this.twoHyphens + this.boundary +
this.twoHyphens + this.crlf);
Flush output buffer:
request.flush();
request.close();
Get response:
InputStream responseStream = new
BufferedInputStream(httpUrlConnection.getInputStream());
BufferedReader responseStreamReader =
new BufferedReader(new InputStreamReader(responseStream));
String line = "";
StringBuilder stringBuilder = new StringBuilder();
while ((line = responseStreamReader.readLine()) != null) {
stringBuilder.append(line).append("\n");
}
responseStreamReader.close();
String response = stringBuilder.toString();
Close response stream:
responseStream.close();
Close the connection:
httpUrlConnection.disconnect();
PS: Of course I had to wrap the request in private class AsyncUploadBitmaps extends AsyncTask<Bitmap, Void, String>
, in order to make the Android platform happy, because it doesn't like to have network requests on the main thread.