How do you send data in a Request body using HttpURLConnection?

Question

I am using HttpURLConnection to make a POST request to a local service deployed locally and created using JAVA Spark. I want to send some data in request body when I make the POST call using the HttpURLConnection but every time the request body in JAVA Spark is null. Below is the code I am using for this

Java Spark POST Service Handler

post("/", (req, res) -> {
    System.out.println("Request Body: " + req.body());
    return "Hello!!!!";
});

HTTPClass making the POST call

public class HTTPClassExample{
    public static void main(String[] args) {
        try{
            URL url = new URL("http://localhost:4567/");
            HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();
            httpCon.setDoOutput(true);
            httpCon.setRequestMethod("POST");
            httpCon.connect();
            OutputStream os = httpCon.getOutputStream();
            OutputStreamWriter osw = new OutputStreamWriter(os, "UTF-8");    
            osw.write("Just Some Text");
            System.out.println(httpCon.getResponseCode());
            System.out.println(httpCon.getResponseMessage());
            osw.flush();
            osw.close();  
        } catch(Exception ex){
            ex.printStackTrace();
        }
    }
}

Eudemonics

Answer 1

You should call httpCon.connect(); only after you write your parameters in the body and not before. Your code should look like this:

URL url = new URL("http://localhost:4567/");
HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();
httpCon.setDoOutput(true);
httpCon.setRequestMethod("POST");
OutputStream os = httpCon.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os, "UTF-8");    
osw.write("Just Some Text");
osw.flush();
osw.close();
os.close();  //don't forget to close the OutputStream
httpCon.connect();

//read the inputstream and print it
String result;
BufferedInputStream bis = new BufferedInputStream(httpCon.getInputStream());
ByteArrayOutputStream buf = new ByteArrayOutputStream();
int result2 = bis.read();
while(result2 != -1) {
    buf.write((byte) result2);
    result2 = bis.read();
}
result = buf.toString();
System.out.println(result);

Everywhere

It appears this is not true. Calling getOutputStream calls connect under the covers. If you want to explicitly connect, call connect before getOutputStream. To test yourself, disable your internet and when the connection fails, you'll see getOutputStream called connect which failed. – Agenda

Answer 2

I posted with the requested data in XML format and the code look like this. You should add the request property Accept and Content-Type also.

URL url = new URL("....");
HttpURLConnection httpConnection = (HttpURLConnection) url.openConnection();

httpConnection.setRequestMethod("POST");
httpConnection.setRequestProperty("Accept", "application/xml");
httpConnection.setRequestProperty("Content-Type", "application/xml");

httpConnection.setDoOutput(true);
OutputStream outStream = httpConnection.getOutputStream();
OutputStreamWriter outStreamWriter = new OutputStreamWriter(outStream, "UTF-8");
outStreamWriter.write(requestedXml);
outStreamWriter.flush();
outStreamWriter.close();
outStream.close();

System.out.println(httpConnection.getResponseCode());
System.out.println(httpConnection.getResponseMessage());

InputStream xml = httpConnection.getInputStream();

Knobby