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HTTP POST Request with Json body giving error code 400

I'm trying to send a Json format in body of POST request in java.
I tried a lot of codes from the internet and StackOverflow, but nothing is working.
I keep getting java.io.IOException: Server returned HTTP response code: 400 for URL: http://localhost:8080/engine-rest/message.
After trying a lot on Postman i noticed it only accepts Json format body, i tried using json libraries like Gson, yet still nothing worked.
Any ideas on how to fix my code? Again I did try to copy a lot of codes from the internet so please don't send me a similar title stackoverflow thread and call the question repetitive.
Thank you in advance.
public class PostRequest {
FileWriter myWriter;
URL url;
public void sendPost(String Url) throws IOException {
String name = "{\"messageName\": \"URLFound\", \"businessKey\": \"3\"}";
try {
myWriter = new FileWriter("C:\\Users\\test\\Desktop\\camunda test save\\Post.txt");
url = new URL ("http://localhost:8080/engine-rest" + Url);
HttpURLConnection http = (HttpURLConnection)url.openConnection();
http.setRequestMethod("POST");
http.setDoOutput(true);
http.setRequestProperty("Content-Type", "application/json");
OutputStream os = http.getOutputStream();
byte[] input = name.getBytes("utf-8");
os.write(input, 0, input.length);
BufferedReader in = new BufferedReader(new InputStreamReader(http.getInputStream()));
StringBuffer response = new StringBuffer();
while ((in.ready())) {
response.append(in.readLine());
}
in.close();
//Writing result on .txt
myWriter.append(response.toString() + "\n" +url);
}
catch(Exception e){
myWriter.append(e.toString());
}
myWriter.close();
}
}

How about using this client project?
https://github.com/camunda-community-hub/camunda-rest-client-spring-boot/
For example:
https://github.com/camunda-community-hub/camunda-rest-client-spring-boot/blob/dce6bd777e3350dd30286311c5351aa9460a34f4/examples/example/src/main/java/org/camunda/bpm/extension/rest/example/standalone/client/ProcessClient.java#L98

Java cant create an object from your json. Check if all fields are sent in the request body of the java class that is expected on the backend side.

Microsoft Graph: Requesting an Extension returns http 400 bad request

I added an open extension to an event in a calendar and am trying to read it back.
Here is the url:
https://graph.microsoft.com/v1.0/users/{userid}/calendars/{calendarId}=/events?$expand=Extensions($filter=Id eq 'c.i.m.p.server.entities.outlook.Event')
I cannot get this to work in a Java program. The following combinations do work:
It works my Java program if I remove the $expand... parameter. I can also ask for certain fields, that works too.
The request works in Postman (I just have to set the token)
The request works in Graph Explorer when I log in as the owner of the calendar
Here is the extension (inside one of the events) when I use Postman to read the event. It is the last item in the event:
"extensions#odata.context": "https://graph.microsoft.com/v1.0/$metadata#users('{userid}')/calendars('{calendarId}')/events('{eventId})/extensions",
"extensions": [
{
"#odata.type": "#microsoft.graph.openTypeExtension",
"id": "Microsoft.OutlookServices.OpenTypeExtension.c.i.m.p.server.entities.outlook.Event",
"extensionName": "c.i.m.p.server.entities.outlook.Event",
"adherentId": "12346",
"timeSlotID": "346463"
}
]
Here is the Java code (Java 8, using java.io and java.net libraries):
private static void doSomething(String _accessToken) throws IOException {
String urlString = "https://graph.microsoft.com/v1.0/users/{userId}/calendars/{calendarId}/events?$expand=Extensions($filter=Id eq 'c.i.m.p.server.entities.outlook.Event')";
URL url = new URL(urlString);
Proxy webProxy
= new Proxy(Proxy.Type.HTTP, new InetSocketAddress({proxy-address}, {port}));
HttpURLConnection connection = (HttpURLConnection) url.openConnection(webProxy);
// Set the appropriate header fields in the request header.
connection.setRequestProperty("Authorization", "Bearer " + _accessToken);
connection.setRequestProperty("Accept", "application/json");
connection.setDoOutput(true);
connection.setReadTimeout(5000);
connection.setRequestMethod(HttpMethod.GET);
try {
connection.connect();
int responseCode = connection.getResponseCode();
System.out.println("execute(), response code = " + responseCode);
String responseMessage = connection.getResponseMessage();
System.out.println("execute(), response Message = " + responseMessage);
String responseString = null;
try {
InputStream ins = connection.getInputStream();
BufferedReader br=new BufferedReader(new InputStreamReader(ins));
StringBuffer sb=new StringBuffer();
String line;
while ((line=br.readLine()) != null) {
sb.append(line);
}
responseString = sb.toString();
} catch (Exception e) {
System.out.println("Could not get input stream from response, error is " + e.toString());
}
System.out.println("execute(), httpResult = " + responseString);
} catch (IOException e) {
System.out.println(".execute(), IOException : " + e.toString());
} finally {
connection.disconnect();
}
}
How do I fix this? Thanks!

400 means bad request. It could be because of url encoding. Url encode the query string.
Something like
String query = "Extensions($filter=Id eq 'c.i.m.p.server.entities.outlook.Event'";
String url = "https://graph.microsoft.com/v1.0/users/{userId}/calendars/{calendarId}/events?
$expand=" + URLEncoder.encode(query, StandardCharsets.UTF_8.name());
Alternatively you could use graph service java api based on your need which will help abstract all the interactions for you or you could use any of the rest clients available.

First of all, you should provide more info on the error - Stacktrace and error message. But 400 code indicates that was a user mistake, meaning that you are sending an invalid request. Since you say that postman request works then compare all the headers that are sent by postman and see if your code misses some hearer. As for the code, instead of coding your own Http client functionality I would suggest using 3d party Http client. Here are a few suggestions:
Apache Http client - very popular and well known 3d party Http Client
OK Http client - Open-source Http client. Here is tutorial
MgntUtils Http client - very simple 3d party HttpClient: Provided in MgntUtils Open source library (written by me). Very simple in use. Take a look at Javadoc. Library itself provided as Maven artifacts and on Git (including source code and Javadoc).

uploading files to a dataset in CKAN / datahub.io through a Java client

I am testing the uploading of files to a dataset on CKAN / datahub.io through a Java client of the API.
public String uploadFile()
throws CKANException {
String returned_json = this._connection.MultiPartPost("", "");
System.out.println("r: " + returned_json);
return returned_json;
}
and
protected String MultiPartPost(String path, String data)
throws CKANException {
URL url = null;
try {
url = new URL(this.m_host + ":" + this.m_port + path);
} catch (MalformedURLException mue) {
System.err.println(mue);
return null;
}
String body = "";
HttpClient httpclient = new DefaultHttpClient();
try {
String fileName = "D:\\test.jpg";
FileBody bin = new FileBody(new File(fileName),"image/jpeg");
StringBody comment = new StringBody("Filename: " + fileName);
MultipartEntity reqEntity = new MultipartEntity();
reqEntity.addPart("bin", bin);
reqEntity.addPart("comment", comment);
HttpPost postRequest = new HttpPost("http://datahub.io/api/storage/auth/form/2013-01-24T130158/test.jpg");
postRequest.setEntity(reqEntity);
postRequest.setHeader("X-CKAN-API-Key", this._apikey);
HttpResponse response = httpclient.execute(postRequest);
int statusCode = response.getStatusLine().getStatusCode();
System.out.println("status code: " + statusCode);
BufferedReader br = new BufferedReader(
new InputStreamReader((response.getEntity().getContent())));
String line;
while ((line = br.readLine()) != null) {
body += line;
}
System.out.println("body: " + body);
} catch (IOException ioe) {
System.out.println(ioe);
} finally {
httpclient.getConnectionManager().shutdown();
}
return body;
}
2 responses I get to my POST request:
a 413 error ("request entity too large") when the jpeg I try to upload is 2.83 Mb. This disappears when I shrink the file to a smaller size. Is there a limit to file size uploads?
a 500 error ("internal server error"). This is where I am stuck. It might have to do with the fact that my dataset on datahub.io is not "datastore enabled"? (I see a disabled "Data API" button next to my resource files in the dataset, with a tooltip saying:
"Data API is unavailable for this resource as DataStore is disabled"
=> is it a possible reason for this 500 error? If so, how could I enable it from the client side? (pointers to Python code would be useful!)
Thx!
PS: the dataset I am using for testing purposes: http://datahub.io/dataset/testapi

Only someone with access to the exception log could tell you why the 500 is occurring.
However, I'd check your request is the same as what you'd get from the python client that was written alongside the datastore: https://github.com/okfn/ckanclient/blob/master/ckanclient/init.py#L546
You're sending the "bin" image buffer and "comment" file_key in your multipart request. Note the file_key must be changed for every upload, so add in a timestamp or something. And maybe you need to add in a Content-Type: for the binary.

I have been going through the same kind of troubles as the poster of this question. After quite a bit of trial and error, I came up with a solution to the problem. In my case, I had some control over the CKAN repository that I wanted to upload to. If you don't, your problem might be impossible to solve...
I assume you are using the 1.8 version of CKAN?
First of all, check whether the CKAN repository has been set up to allow file upload and if not, configure it to allow that. This can be done on the server using the steps posted here: http://docs.ckan.org/en/ckan-1.8/filestore.html#local-file-storage
The 413 error that you mentioned should be adressed next. This has to do with the general configuration of the server. In my case, the CKAN was hosted through nginx. I added a "client_max_body_size 100M" line to the nginx.conf file. See this post for instance: http://recursive-design.com/blog/2009/11/18/nginx-error-413-request-entity-too-large/
Then there is only the 500 error left. At the time of this writing, the api documentation of CKAN is still a little immature... It does indeed say that you have to build a request like you have made for file upload. However, this request is just to ask for permission for the file upload. If your credentials check out for file upload (not every user may be allowed to upload files), the response holds an object telling you where to send your file to... Because of the unclear api, you ended up merging these two requests.
The following scenario shows a follow up of two requests to handle the file upload. It might be that some steps in the scenario work out differently in your case, because of a repository that has been set up a little differently. If you get error messages, please be sure to check the response's body for clues!
Here is the authentication request that I used:
String body = "";
String generatedFilename=null;
HttpClient httpclient = new DefaultHttpClient();
try {
// create new identifier for every file, use time
SimpleDateFormat dateFormatGmt = new SimpleDateFormat("yyyyMMMddHHmmss");
dateFormatGmt.setTimeZone(TimeZone.getTimeZone("GMT"));
String date=dateFormatGmt.format(new Date());
generatedFilename=date +"/"+filename;
HttpGet getRequest = new HttpGet(this.CKANrepos+ "/api/storage/auth/form/"+generatedFilename);
getRequest.setHeader(CKANapiHeader, this.CKANapi);
HttpResponse response = httpclient.execute(getRequest);
int statusCode = response.getStatusLine().getStatusCode();
BufferedReader br = new BufferedReader(
new InputStreamReader((response.getEntity().getContent())));
String line;
while ((line = br.readLine()) != null) {
body += line;
}
if(statusCode!=200){
throw new IllegalStateException("File reservation failed, server responded with code: "+statusCode+
"\n\nThe message was: "+body);
}
}finally {
httpclient.getConnectionManager().shutdown();
}
Now, if all goes well, the server responds with a json object holding the parameters to use when doing the actual file upload. In my case, the object looked like:
{file_key:"some-filename-to-use-when-uploading"}
Be sure to check the json object though, as I'm given to understand that there may be custom ckan repositories that require more or different parameters.
These responses can then be used in the actual file upload:
File file = new File("/tmp/file.rdf");
String body = "";
HttpClient httpclient = new DefaultHttpClient();
try {
FileBody bin = new FileBody(file,"application/rdf+xml");
MultipartEntity reqEntity = new MultipartEntity();
reqEntity.addPart("file", bin);
reqEntity.addPart("key", new StringBody(filename));
HttpPost postRequest = new HttpPost(this.CKANrepos+"/storage/upload_handle");
postRequest.setEntity(reqEntity);
postRequest.setHeader(CKANapiHeader, this.CKANapi);
HttpResponse response = httpclient.execute(postRequest);
int statusCode = response.getStatusLine().getStatusCode();
BufferedReader br = new BufferedReader(
new InputStreamReader((response.getEntity().getContent())));
String line;
while ((line = br.readLine()) != null) {
body += line;
}
if(statusCode!=200){
getWindow().showNotification("Upload Statuscode: "+statusCode,
body,
Window.Notification.TYPE_ERROR_MESSAGE);
}
}finally {
httpclient.getConnectionManager().shutdown();
}
as you can see, the file_key property has now been transformed into the simple 'key' property. I don't know why.
This will get your file uploaded. The response to this upload request will hold a json object telling you where the file got uploaded to. edit: actually it seems that my ckan responded with a simple html page to tell me that the file got uploaded... I had to parse the page to confirm that the file was uploaded correctly :(
In my case, the file was at
this.CKANrepos +"/storage/f/"+location
where location is the filename returned in the authentication phase.
In the previous code fragments:
//the location of your ckan repository, including /api and possibly version, e.g.
this.CKANrepos = "http://datahub.io/api/3/";
this.CKANapiHeader="X-CKAN-API-Key";
this.CKANapi = "your ckan api key here";

How to upload data using POST-query?

I have following problem: I'm developing the application which need to authorize on server and upload data from my mobile into it. The server side is ready and works correctly. So, for authorizing I use the following code:
URL url = new URL(VALIDATING_URL);
URLConnection connection=url.openConnection();
connection.setDoOutput(true);
PrintWriter out=new PrintWriter(connection.getOutputStream());
out.print(POST_QUERY_EMAIL+email);
out.print("&");
out.print(POST_QUERY_PASS+password);
out.print("&");
out.print(POST_QUERY_CHANNEL+channel);
out.close();
Scanner in=new Scanner(connection.getInputStream());
StringBuilder result=new StringBuilder();
while (in.hasNextLine()) {
result.append(in.nextLine());
result.append("\n");
}
in.close();
It works correctly, and the application will get needed result if I enter correctly data. So, now I need to upload data into server using POST-query, but I don't know how I can do it. Using HTML forms, video is usually uploaded using 'userfile' variable and will be got from $_FILES array in PHP scipts. How can I upload do it from Java? Can I just print data into PrintStream from InputStream?
Thank you, I hope you can help me

Try this,
public void postData() throws Exception {
HttpClient client = new DefaultHttpClient();
HttpPost httppost = new HttpPost("https://www.xyz.com");
List<NameValuePair> list = new ArrayList<NameValuePair>(1);
list.add(new BasicNameValuePair("name","ABC");
httppost.setEntity(new UrlEncodedFormEntity(list));
HttpResponse r = client.execute(httppost);
}

I would suggest reading this. It shows you how to do a POST with URLConnection and explains what's going on.

JSON URL from StackExchange API returning jibberish?

I have a feeling I'm doing something wrong here, but I'm not quite sure if I'm missing a step, or am just having an encoding problem or something. Here's my code:
URL url = new URL("http://api.stackoverflow.com/0.8/questions/2886661");
BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
// Question q = new Gson().fromJson(in, Question.class);
String line;
StringBuffer content = new StringBuffer();
while ((line = in.readLine()) != null)
{
content.append(line);
}
When I print content, I get a whole bunch of wingdings and special characters, basically jibberish. I would copy and past it here, but that isn't working. What am I doing wrong?

In this case it's not a character encoding problem, it's a content encoding problem; you're expecting text, but the server is using compression to save bandwidth. If you look at the headers when you grab that url, you can see the server you are connecting to is returning gzipped content:
GET /0.8/questions/2886661 HTTP/1.1
Host: api.stackoverflow.com
HTTP/1.1 200 OK
Server: nginx
Date: Sat, 22 May 2010 15:51:34 GMT
Content-Type: application/json; charset=utf-8
<more headers>
Content-Encoding: gzip
<more headers>
So you either need to use a smarter client like Apache's HttpClient as stevedbrown suggests (although you need a tweak to get it to speak Gzip automatically), or explicitly decompress the stream you got in your example code. Try this instead for the line where you declare your input:
BufferedReader in = new BufferedReader(new InputStreamReader(new GZIPInputStream(url.openStream())));
I've verified that this works for the url you are trying to grab.

Use the Apache Http Client instead, it's going to take care of character conversions properly. From that site's examples:
public final static void main(String[] args) throws Exception {
HttpClient httpclient = new DefaultHttpClient();
HttpGet httpget =
new HttpGet("http://api.stackoverflow.com/0.8/questions/2886661");
System.out.println("executing request " + httpget.getURI());
// Create a response handler
ResponseHandler<String> responseHandler = new BasicResponseHandler();
String responseBody = httpclient.execute(httpget, responseHandler);
System.out.println(responseBody);
System.out.println("----------------------------------------");
// When HttpClient instance is no longer needed,
// shut down the connection manager to ensure
// immediate deallocation of all system resources
httpclient.getConnectionManager().shutdown();
}
In this case, see http://svn.apache.org/repos/asf/httpcomponents/httpclient/branches/4.0.x/httpclient/src/examples/org/apache/http/examples/client/ClientGZipContentCompression.java, which shows how to deal with Gzip content.

Sometimes the API call response are compressed eg. StackExchange API. Please go through their documentation and check for the compression they are using. Some use either GZIP or DEFLATE compression.In case of GZIP compression use the following.
InputStream is = new URL(url).openStream();
BufferedReader in = new BufferedReader(new InputStreamReader(new GZIPInputStream(is)));