HttpURLConnection中的content-length

Question

I'm trying to send a body in x-www-form-urlencoded to my local Web API. I can make GET without any problems. Here is what I do:

    String urlParameters = "user=User&label=GPU+Temp&file=src%2FDataSource0.txt&backgroundColor=rgb(255%2C255%2C255%2C0)&borderColor=rgb(255%2C255%2C255%2C0)&pointBorderColor=rgb(255%2C255%2C255%2C0)&pointHoverBackgroundColor=rgb(255%2C255%2C255%2C0)&pointHoverBorderColor=rgb(255%2C255%2C255%2C0)&min=0&max=100&stepSize=50";

    byte[] postData = urlParameters.getBytes(Charset.forName("UTF-8"));
    int postDataLength = postData.length;
    String request = "http://192.168.1.30:6262/api/values";
    URL url = new URL(request);
    con = (HttpURLConnection) url.openConnection();
    con.setDoOutput(true);
    con.setInstanceFollowRedirects(false);
    con.setRequestMethod("POST");
    con.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
    con.setRequestProperty("charset", "utf-8");
    con.setRequestProperty("Content-Length", Integer.toString(postDataLength));
    con.connect();

java.net.ProtocolException: content-length promised 598 bytes, but received 0

So it means that I'm not sending any data in my POST , how come?

Answer 1

Using con.setRequestProperty("Content-Length", Integer.toString(postDataLength)); you're just sending the lenght of your postDataLength , you're not actually setting it's body. In order to actually send your variable to the webservice you need to do this before calling the connect() :

OutputStream os = con.getOutputStream();
os.write(urlParameters.getBytes("UTF-8"));
os.close();

Answer 2

You need do this:

            body = datos.toString();
            content_bytes = body.getBytes("UTF-8");
            content_length = content_bytes.length;



            // establecer headers.
            connection.setRequestProperty( "Content-Type", "application/json; charset=utf-8" );
            connection.setRequestProperty( "Content-Length", Integer.toString( content_length  ) );

.....

            dataOutputStream = new DataOutputStream( connection.getOutputStream() );
            dataOutputStream.write(body.getBytes("UTF-8"));