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Can't set "POST" request to HttpURLConnection object

I'm going to connect satang api server with java.
In the following code con object can't set "POST" request.
I don't know the reason.
Please help me.
public String placeLimitOrder(String amount,String pair,String price,String side) throws IOException, BadResponseException
{
Long lnonce=new Date().getTime();
String nonce=lnonce.toString();
String req="amount="+amount+"&nonce="+nonce+"&pair="+pair+"&price="+price+"&side="+side+"&type=limit";
String operation="orders/?"+req;
String signature=getSignature(req);
StringBuilder result = new StringBuilder();
URL url = new URL(baseUrl+operation);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
con.setDoOutput( true );
con.setInstanceFollowRedirects( false );
con.setRequestMethod("POST");
con.setRequestProperty("Authorization", "TDAX-API "+this.key);
con.setRequestProperty("Signature",signature);
con.setRequestProperty( "Content-Type", "application/x-www-form-urlencoded");
con.setRequestProperty( "charset", "utf-8");
con.setRequestProperty("User-Agent", "java client");
con.setUseCaches( false );
int responseCode=con.getResponseCode();
if(responseCode!=HttpURLConnection.HTTP_OK){
System.out.println(con.getHeaderField("Allow"));
throw new BadResponseException(responseCode);
}
BufferedReader rd = new BufferedReader(new InputStreamReader(con.getInputStream()));
String line;
while ((line = rd.readLine()) != null) {
result.append(line);
}
rd.close();
return result.toString();
}

You are not sending any data through your connection. You have to use:
con.getOutputStream().write(...);
where you shold send your POST request payload as bytes

This is what I have found, I can't say with certainty it is the answer for everyone but hopefully it will shed some light on the problem for many others.
It seems that the internal "method" parameter of the HttpsURLConnection instance IS NOT very related to the requestMethod getter and setter on the instance. If you are like me you revert to using the debugger in android studio because logging in android is abysmal.
On the left I have the Debug inspector showing the contents of the URLConnection instance. On the right I have the results of "Evaluate Expression" on
connection.getRequestMethod() //right side of image
It is frustrating that there are not any definitive answers on this (or many other android questions) and when you try to find them you are often greeted with invitations to use someone else's library. This is not the ideal solution because in many cases using someone else's library requires security vetting.
Hopefully this helps. In my case, things were working correctly but the server was sending back a BAD_REQUEST response because of a bug over there.

I've met same problem.
I've solved this problem with following method.
First. Make your "Content-Type" to "application/json".
And parse the request params to your post body.

Adding value to path parameter in Java REST?

NOTICE UPDATE!!
The problem got solved and i added my own answer in the thread
In short, I have attempted to add the parameter "scan_id" value but since it is a POST i can't add the value directly in the url path.
using the code i already have, how would i go about modifying or adding so that the url is correct, that is, so that it accepts my POST?.
somehow i have been unable to find any examples that have helped me in figuring out how i would go about doing this..
I know how to do a POST with a payload, a GET with params. but a post with Params is very confusing to me.
Appreciate any help. (i'd like to continue using HttpUrlConnection unless an other example is provided that also tells me how to send the request and not only configuring the path.
I've tried adding it to the payload.
I've tried UriBuilder but found it confusing and in contrast with the rest of my code, so wanted to ask for help with HttpUrlConnection.
URL url = new URL("http://localhost/scans/{scan_id}/launch");
HttpURLConnection con = (HttpURLConnection) url.openConnection();
con.setRequestMethod("POST");
con.setRequestProperty("tmp_value_dont_mind_this", "432432");
con.setRequestProperty("X-Cookie", "token=" + "43432");
con.setRequestProperty("X-ApiKeys", "accessKey="+"43234;" + " secretKey="+"43234;");
con.setDoInput(true);
con.setDoOutput(true); //NOT NEEDED FOR GETS
con.setRequestMethod("POST");
con.setRequestProperty("Accept", "application/json");
con.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
//First example of writing (works when writing a payload)
OutputStreamWriter writer = new OutputStreamWriter(con.getOutputStream(), "UTF-8");
writer.write(payload);
writer.close();
//second attemp at writing, doens't work (wanted to replace {scan_id} in the url)
DataOutputStream writer = new DataOutputStream(con.getOutputStream());
writer.writeChars("scan_id=42324"); //tried writing directly
//writer.write(payload);
writer.close();
Exception:
Exception in thread "main" java.io.IOException: Server returned HTTP response code: 400 for URL: http://localhost/scans/launch
I'd like one of the three response codes because then i know the Url is correct:
200 Returned if the scan was successfully launched.
403 Returned if the scan is disabled.
404 Returned if the scan does not exist.
I've tried several urls
localhost/scans/launch,
localhost/scans//launch,
localhost/scans/?/launch,
localhost/scans/{scan_id}/launch,

So with the help of a friend and everyone here i solved my problem.
The below code is all the code in an entire class explained bit by bit. at the bottom you have the full class with all its syntax etc, that takes parameters and returns a string.
in a HTTP request there are certain sections.
Such sections include in my case, Request headers, parameters in the Url and a Payload.
depending on the API certain variables required by the API need to go into their respective category.
My ORIGINAL URL looked like this: "http://host:port/scans/{scan_id}/export?{history_id}"
I CHANGED to: "https://host:port/scans/" + scan_Id + "/export?history_id=" + ID;
and the API i am calling required an argument in the payload called "format" with a value.
String payload = "{\"format\" : \"csv\"}";
So with my new URL i opened a connection and set the request headers i needed to set.
HttpsURLConnection con = (HttpsURLConnection) url.openConnection();
The setDoOutput should be commented out when making a GET request.
con.setDoInput(true);
con.setDoOutput(true);
con.setRequestMethod("POST");
con.setRequestProperty("Accept", "application/json");
con.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
con.setRequestProperty("X-Cookie", "token=" + token);
con.setRequestProperty("X-ApiKeys", "accessKey="+"23243;" +"secretKey="+"45543;");
Here i write to the payload.
//WRITING THE PAYLOAD to the http call
OutputStreamWriter writer = new OutputStreamWriter(con.getOutputStream(), "UTF-8");
writer.write(payload);
writer.close();
After i've written the payload i read whatever response i get back (this depends on the call, when i do a file download (GET Request) i don't have a response to read as i've already read the response through another piece of code).
I hope this helps anyone who might encounter this thread.
public String requestScan(int scan_Id, String token, String ID) throws MalformedInputException, ProtocolException, IOException {
try {
String endpoint = "https://host:port/scans/" + scan_Id + "/export?history_id=" ID;
URL url = new URL(endpoint);
String payload= "{\"format\" : \"csv\"}";
HttpsURLConnection con = (HttpsURLConnection) url.openConnection();
con.setDoInput(true);
con.setDoOutput(true);
con.setRequestMethod("POST");
con.setRequestProperty("Accept", "application/json");
con.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
con.setRequestProperty("X-Cookie", "token=" + token);
con.setRequestProperty("X-ApiKeys", "accessKey="+"324324;" +
"secretKey="+"43242;");
//WRITING THE PAYLOAD to the http call
OutputStreamWriter writer = new OutputStreamWriter(con.getOutputStream(), "UTF-8");
writer.write(payload);
writer.close();
//READING RESPONSE
BufferedReader br = new BufferedReader(new InputStreamReader(con.getInputStream()));
StringBuffer jsonString = new StringBuffer();
String line;
while ((line = br.readLine()) != null) {
jsonString.append(line);
}
br.close();
con.disconnect();
return jsonString.toString();
} catch (Exception e) {
throw new RuntimeException(e.getMessage());
}
}

As discussed here the solution would be to change the content type to application/x-www-form-urlencoded, but since you are already using application/json; charset=UTF-8 (which I am assuming is a requirement of your project) you have no choise to redesign the whole thing. I suggest you one of the following:
Add another GET service;
Add another POST service with content type application/x-www-form-urlencoded;
Replace this service with one of the above.
Do not specify the content type at all so the client will accept anything. (Don't know if possible in java)
If there are another solutions I'm not aware of, I don't know how much they would be compliant to HTTP protocol.
(More info)
Hope I helped!

Why you are not using like this. Since you need to do a POST with HttpURLConnection, you need to write the parameters to the connection after you have opened the connection.
String urlParameters = "scan_id=42324";
byte[] postData = urlParameters.getBytes(StandardCharsets.UTF_8);
DataOutputStream dataOutputStream = new DataOutputStream(conn.getOutputStream());
dataOutputStream.write(postData);
Or if you have launch in the end, just change the above code to the following,
String urlParameters = "42324/launch";
byte[] postData = urlParameters.getBytes(StandardCharsets.UTF_8);
DataOutputStream dataOutputStream = new DataOutputStream(conn.getOutputStream());
dataOutputStream.write(postData);

URL url = new URL("http://localhost/scans/{scan_id}/launch");
That line looks odd to me; it seems you are trying to use a URL where you are intending the behavior of a URI Template.
The exact syntax will depend on which template implementation you choose; an implementation using the Spring libraries might look like:
import org.springframework.web.util.UriTemplate;
import java.net.url;
// Warning - UNTESTED code ahead
UriTemplate template = new UriTemplate("http://localhost/scans/{scan_id}/launch");
Map<String,String> uriVariables = Collections.singletonMap("scan_id", "42324");
URI uri = template.expand(uriVariables);
URL url = uri.toURL();

Why HttpURLConnection does not send data unless I try to receive something

I cannot comprehend why doesn't the following code does not put a packet onto wire (confirmed via wireshark). It is a fairly standard method of sending an HTTP POST request, as I believe. I don't intend to read anything just POST.
private void sendRequest() throws IOException {
String params = "param=value";
URL url = new URL(otherUrl.toString());
HttpURLConnection con = (HttpURLConnection)url.openConnection();
con.setDoOutput(true);
con.setDoInput(true); //setting this to `false` does not help
con.setRequestMethod("POST");
con.setRequestProperty("Content-Type", "text/plain");
con.setRequestProperty("Content-Length", "" + Integer.toString(params.getBytes().length));
con.setRequestProperty("Accept", "text/plain");
con.setUseCaches(false);
con.connect();
DataOutputStream wr = new DataOutputStream(con.getOutputStream());
wr.writeBytes(params);
wr.flush();
wr.close();
//Logger.getLogger("log").info("URL: "+url+", response: "+con.getResponseCode());
con.disconnect();
}
What happens is... actually nothing, unless I try to read anything. For example by uncommenting the above log line which reads the response code. Trying to read a response via con.getInputStream(); also works. There is no movement of packets. When I uncomment the getResponseCode, I can see that http POST is sent, and then 200 OK is sent back. The order is proper. I.e. I don't get some wild response before sending POST. Everything else looks exactly the same (I can attach wireshark screenshots if needed.). In the debugger the code executes (i.e. does not block anywhere).
I don't understand under what circumstances this can be happening. I belive it should be possible, to send a POST request with con.setDoInput(false);. Currently it doesn't send anything or fails (when trying to execute con.getResponseCode()) with an exception because I obviously promised I won't read anything.
It might be relevant, that before sendRequest I do request some data from the same site, but I trust I close everything properly. I.e:
public static String getData(String urlAddress) throws MalformedURLException, IOException {
URL url = new URL(urlAddress);
HttpURLConnection con = (HttpURLConnection)url.openConnection();
con.setDoOutput(false);
InputStream in = con.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(in));
StringBuilder data = new StringBuilder();
String line;
while((line = reader.readLine()) != null) {
data.append(line);
}
reader.close();
in.close();
con.getResponseCode();
con.disconnect();
return data.toString();
}
The server for url in both cases is the same, port also, so I believe it is possible to use the same socket for communication. The above code works and retrieves the data properly.
I am not sure, maybe I don't clean something, and it gets cached, so with out an explicit read the POST gets delayed. There is no other traffic on the socket.

Unless you're using fixed-length or chunked transfer mode, HttpURLConnection will buffer all your output until you call getInputStream() or getResponseCode(), so that it can send a correct Content-length header.
If you call getResponseCode() you should have a look at its value.

HttpURLConnection getInputStream() has one second delay

I am using HttpURLConnection for making POST requests. I observe always the same behaviour during tests:
first request runs very fast (miliseconds)
all following requests take one second + some miliseconds
So something is causing 1 second delay. What can it be? The delay is happening exactly in HttpURLConnection#getInputStream().
I replaced the implementation with HttpClient - then everything is OK, no second delays (so it is not the server fault). But I really don't want to use any external dependency, so I would like to fix the HttpURLConnection thing... Any ideas?
Below current implementation. I tried some tips from stackoverflow (adding headers to the request), but with no success.
URL obj = new URL(url);
HttpURLConnection con = (HttpURLConnection) obj.openConnection();
con.setRequestMethod("POST");
con.setRequestProperty("Content-Length", ""
+ (body == null ? 0 : body.length));
// Send post request
con.setDoOutput(true);
OutputStream wr = con.getOutputStream();
if (body != null) {
wr.write(body);
}
wr.flush();
wr.close();
BufferedReader rd = new BufferedReader(new InputStreamReader(
con.getInputStream()));
String line;
String result = "";
while ((line = rd.readLine()) != null) {
result += line;
}
rd.close();
con.disconnect();
return result;
PS: It is about jse, not android.

You're never closing the input stream from the connection - that may mean that the connection isn't eligible for pooling, and on the next attempt it's waiting for up to a second to see if the previous request's connection will become eligible for pooling.
At the very least, it would be a good idea to close the stream. Use a try-with-resources block if you're using Java 7 - and ditto for the writer.
As an aside, I suggest you explicitly state the encoding you expect when reading - or use a higher-level library which detects that automatically based on headers.

Java connecting to Http which method to use?

I have been looking around at different ways to connect to URLs and there seem to be a few.
My requirements are to do POST and GET queries on a URL and retrieve the result.
I have seen
URL class
DefaultHttpClient class
HttpClient - apache commons
which method is best?

My rule of thumb and recommendation: Don't introduce dependencies and 3rd party libraries if it's fairly easy to get away without.
In this case I would say, if you need efficiency such as multiple requests per established connection session handling or cookie support etc, go for HTTPClient.
If you only need to perform an HTTP get, this will suffice:
Getting Text from a URL
try {
// Create a URL for the desired page
URL url = new URL("http://hostname:80/index.html");
// Read all the text returned by the server
BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
String str;
while ((str = in.readLine()) != null) {
// str is one line of text; readLine() strips the newline character(s)
}
in.close();
} catch (MalformedURLException e) {
} catch (IOException e) {
}
Sending a POST Request Using a URL
try {
// Construct data
String data = URLEncoder.encode("key1", "UTF-8") + "=" + URLEncoder.encode("value1", "UTF-8");
data += "&" + URLEncoder.encode("key2", "UTF-8") + "=" + URLEncoder.encode("value2", "UTF-8");
// Send data
URL url = new URL("http://hostname:80/cgi");
URLConnection conn = url.openConnection();
conn.setDoOutput(true);
OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());
wr.write(data);
wr.flush();
// Get the response
BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));
String line;
while ((line = rd.readLine()) != null) {
// Process line...
}
wr.close();
rd.close();
} catch (Exception e) {
}
Both methods work great. (I've even done manual gets/posts with cookies.)

HTTPClient is the way to go if your needs go past trivial URL connection (e.g. proxy authentication such as NTLM). There are at least a comparison here between standard HTTP client functionality between libraries provided by the JRE, Apache HTTP Client and others.

If you are using JDK versions earlier to (including 1.4) and have a fairly large data in your post requests, like large file uploads, the default HTTPURLConnection that comes with the JRE is bound to go Out of memory at some point since it buffers the entire data before posting. Additionally it does not support some advanced HTTP headers like chunked encoding, etc.
So I'd recommend it only if your request are trivial and you are not posting large data as aioobe did.