Tomcat returns http response code 400 - http

Question

I was googling for a long time, but still can't find a solution to my case.
My Tomcat sometimes returns an exception :
Error in postRequest(): Server returned HTTP response code: 400 for URL: http://localhost:80/CITIUS2/webresources/entities.personainterna/
Sometimes it works and sometimes it returns this exception, so I really don't know what is the reason...
Connection function:
public static String excutePost(String targetURL, String urlParameters) throws UnsupportedEncodingException {
URL url;
HttpURLConnection connection = null;
String responseXML = null;
try {
//Create connection
url = new URL(targetURL);
connection = (HttpURLConnection) url.openConnection();
byte[] requestXML = urlParameters.getBytes();
connection.setRequestProperty("Content-Length", String.valueOf(requestXML.length));
connection.setRequestProperty("Content-Type", "application/xml; charset=utf-8");
connection.setRequestMethod("POST");
connection.setDoOutput(true);
connection.setDoInput(true);
// Send the String that was read into postByte.
OutputStream out = connection.getOutputStream();
out.write(requestXML);
out.close();
// Read the response and write it to standard out.
InputStreamReader isr = new InputStreamReader(connection.getInputStream());
BufferedReader br = new BufferedReader(isr);
String temp;
String tempResponse = "";
//Create a string using response from web services
while ((temp = br.readLine()) != null) {
tempResponse = tempResponse + temp;
}
responseXML = tempResponse;
br.close();
isr.close();
} catch (java.net.MalformedURLException e) {
System.out.println("Error in postRequest(): Secure Service Required");
} catch (Exception e) {
System.out.println("Error in postRequest(): " + e.getMessage());
}
return responseXML;
}
# Edit:
In general build is successful, there are no errors, only this one in the Apache Tomcat's output window.
Rest method:
#POST
#Consumes({"application/xml", "application/json"})
public Response create(Personainterna entity) {
try {
getJpaController().create(entity);
return Response.created(URI.create(entity.getPersonaId().toString())).build();
} catch (Exception ex) {
return Response.notModified(ex.getMessage()).build();
}
}