Blog : Java - sending HTTP parameters via POST method easily

Java - sending HTTP parameters via POST method easily
I am successfully using this code to send HTTP requests with some parameters via GET method
function void sendRequest(String request)
{
  // i.e.: request = "http://example.com/index.php?param1=a&param2=b&param3=c";
  URL url = new URL(request);
  HttpURLConnection connection = (HttpURLConnection) url.openConnection();   
  connection.setDoOutput(true);
  connection.setInstanceFollowRedirects(false);
  connection.setRequestMethod("GET");
  connection.setRequestProperty("Content-Type", "text/plain");
  connection.setRequestProperty("charset", "utf-8");
  connection.connect();
}

How can I change the code above as little as possible to be able to send paramters either via GET or POSt?
I was hoping that changing
connection.setRequestMethod("GET");
to
connection.setRequestMethod("POST");
would have done the trick, but the parameters are still sent via GET method.
Has HttpURLConnection got any method that would help? Is there any helpful Java construct?
Any help would be very much appreciated.
In a GET request, the parameters are sent as part of the URL.
In a POST request, the parameters are sent as a body of the request, after the headers.
To do a POST with HttpURLConnection, you need to write the parameters to the connection after you have opened the connection.
This code should get you started:
String urlParameters = "param1=a&param2=b&param3=c";
String request = "http://example.com/index.php";
URL url = new URL(request);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();   
connection.setDoOutput(true);
connection.setDoInput(true);
connection.setInstanceFollowRedirects(false);
connection.setRequestMethod("POST");
connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
connection.setRequestProperty("charset", "utf-8");
connection.setRequestProperty("Content-Length", "" + Integer.toString(urlParameters.getBytes().length));
connection.setUseCaches (false);

DataOutputStream wr = new DataOutputStream(connection.getOutputStream ());
wr.writeBytes(urlParameters);
wr.flush();
wr.close();
connection.disconnect();
I couldn't get Alan's example to actually do the post, so I ended up with this:
String urlParameters = "param1=a&param2=b&param3=c";
URL url = new URL("http://example.com/index.php");
URLConnection conn = url.openConnection();

conn.setDoOutput(true);

OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());

writer.write(urlParameters);
writer.flush();

String line;
BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

while ((line = reader.readLine()) != null) {
  System.out.println(line);
}
writer.close();
reader.close();  
Here is a simple example that submits a form then dumps the result page to System.out. Change the URL and the POST params as appropriate, of course:
import java.io.*;
import java.net.*;
import java.util.*;

class Test {
  public static void main(String[] args) throws Exception {
  URL url = new URL("http://example.net/new-message.php");
  Map<String,Object> params = new LinkedHashMap<>();
  params.put("name", "Freddie the Fish");
  params.put("email", "fishie@seamail.com");
  params.put("reply_to_thread", 10394);
  params.put("message", "Shark attacks in Botany Bay have gotten out of control. We need more defensive dolphins to protect the schools here, but Mayor Porpoise is too busy stuffing his snout with lobsters. He's so shellfish.");

  StringBuilder postData = new StringBuilder();
  for (Map.Entry<String,Object> param : params.entrySet()) {
  if (postData.length() != 0) postData.append('&');
  postData.append(URLEncoder.encode(param.getKey(), "UTF-8"));
  postData.append('=');
  postData.append(URLEncoder.encode(String.valueOf(param.getValue()), "UTF-8"));
  }
  byte[] postDataBytes = postData.toString().getBytes("UTF-8");

  HttpURLConnection conn = (HttpURLConnection)url.openConnection();
  conn.setRequestMethod("POST");
  conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
  conn.setRequestProperty("Content-Length", String.valueOf(postDataBytes.length));
  conn.setDoOutput(true);
  conn.getOutputStream().write(postDataBytes);

  Reader in = new BufferedReader(new InputStreamReader(conn.getInputStream(), "UTF-8"));
  for (int c; (c = in.read()) >= 0; System.out.print((char)c));
  }
}
I find HttpURLConnection really cumbersome to use. And you have to write a lot of boilerplate, error prone code. I needed a lightweight wrapper for my Android projects and came out with a library which you can use as well: DavidWebb.
The above example could be written like this:
Webb webb = Webb.create();
webb.post("http://example.com/index.php")
  .param("param1", "a")
  .param("param2", "b")
  .param("param3", "c")
  .ensureSuccess()
  .asVoid();
You can find a list of alternative libraries on the link provided.