Java - sending HTTP parameters via POST method easily

Question

I am successfully using this code to send HTTP requests with some parameters via GET method

void sendRequest(String request)
{
            


        

Answer 1

For those having trouble receiving the request on a php page using $_POST because you expect key-value pairs:

While all the answers where very helpful, I lacked some basic understanding on which string actually to post, since in the old apache HttpClient I used

new UrlEncodedFormEntity(nameValuePairs); (Java)

and then could use $_POST in php do get the key-value pairs.

To my understanding now one has build that string manually before posting. So the string needs to look like

val data = "key1=val1&key2=val2"

but instead just adding it to the url it is posted (in the header).

The alternative would be to use a json-string instead:

val data = "{\"key1\":\"val1\",\"key2\":\"val2\"}" // {"key1":"val1","key2":"val2"}

and pull it in php without $_POST:

$json_params = file_get_contents('php://input');
// echo_p("Data: $json_params");
$data = json_decode($json_params, true);

Here you find a sample code in Kotlin:

class TaskDownloadTest : AsyncTask() {
    override fun doInBackground(vararg params: Void): Void? {
        var urlConnection: HttpURLConnection? = null

        try {

            val postData = JsonObject()
            postData.addProperty("key1", "val1")
            postData.addProperty("key2", "val2")

            // reformat json to key1=value1&key2=value2
            // keeping json because I may change the php part to interpret json requests, could be a HashMap instead
            val keys = postData.keySet()
            var request = ""
            keys.forEach { key ->
                // Log.i("data", key)
                request += "$key=${postData.get(key)}&"
            }
            request = request.replace("\"", "").removeSuffix("&")
            val requestLength = request.toByteArray().size
            // Warning in Android 9 you need to add a line in the application part of the manifest: android:usesCleartextTraffic="true"
            // https://stackoverflow.com/questions/45940861/android-8-cleartext-http-traffic-not-permitted
            val url = URL("http://10.0.2.2/getdata.php")
            urlConnection = url.openConnection() as HttpURLConnection
            // urlConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded") // apparently default
            // Not sure what these are for, I do not use them
            // urlConnection.setRequestProperty("Content-Type", "application/json")
            // urlConnection.setRequestProperty("Key","Value")
            urlConnection.readTimeout = 5000
            urlConnection.connectTimeout = 5000
            urlConnection.requestMethod = "POST"
            urlConnection.doOutput = true
            // urlConnection.doInput = true
            urlConnection.useCaches = false
            urlConnection.setFixedLengthStreamingMode(requestLength)
            // urlConnection.setChunkedStreamingMode(0) // if you do not want to handle request length which is fine for small requests

            val out = urlConnection.outputStream
            val writer = BufferedWriter(
                OutputStreamWriter(
                    out, "UTF-8"
                )
            )
            writer.write(request)
            // writer.write("{\"key1\":\"val1\",\"key2\":\"val2\"}") // {"key1":"val1","key2":"val2"} JsonFormat or just postData.toString() for $json_params=file_get_contents('php://input'); json_decode($json_params, true); in php
            // writer.write("key1=val1&key2=val2") // key=value format for $_POST in php
            writer.flush()
            writer.close()
            out.close()

            val code = urlConnection.responseCode
            if (code != 200) {
                throw IOException("Invalid response from server: $code")
            }

            val rd = BufferedReader(
                InputStreamReader(
                    urlConnection.inputStream
                )
            )
            var line = rd.readLine()
            while (line != null) {
                Log.i("data", line)
                line = rd.readLine()
            }
        } catch (e: Exception) {
            e.printStackTrace()
        } finally {
            urlConnection?.disconnect()
        }

        return null
    }
}