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Logging JSON Payload in Apache NiFi from Java Application POST request

I'm new to Apache NiFi, and I developed an application to send JSON data to a NiFi endpoint via HTTP POST request.
In Apache NiFi, I have a HandleHTTPRequest processor connected to a PutFile processor then a HandleHTTPResponse processor. I've also tried using a LogAttribute processor. The response code and HTTP message from the NiFi web service is working properly, but I'm trying to make sure my JSON payload is being sent properly. Post is enabled in the HTTPRequest handler. Yet, the only files it's generating are blank and 0kb in size. Any ideas?

Based on the comments above the conclusion is that there was no problem on the side of Nifi.
It's definitely an issue with the Java code, I used postman again after changing some local firewall configurations and it successfully logs any POST requests that are sent to it and puts it in a file
The key step towards resolving the issue was trying to connect with something like Postman as #Binary Nerd and #Brian Bende suggested.

Send additional information over HTTP header

I have written a simple HTTP server using Java and want to send some additional information (puzzle parameters and a small puzzle solver program) to the client i.e. a regular browser.
Similarly, the browser is also supposed to send information (solution) back to the server.
Is there a way to do this by just transmitting this information over the HTTP headers?
Thanks a lot

the headers are usually used to add http protocol relevant information.
You should probably use either the body of the response or cookies to add the needed information.
Adding a cookie is done using the header so it kind of fits what you are asking for.
But I wonder why you need to put it in the header? it seems like what you are asking for is url parameters (client to server) and response body (server to client).

read httppost request messages without a server

I have a third party server that is periodically sending http post request messages to an URL(can be configured). In my application I am reading data by starting a jetty server and listening for data on the configured URL.
Wondering if it is possible to listen for the data sent by the server without starting any server like the jetty?

You can always create a socket yourself and listen at port 80 (or something similar) for HTTP requests. See http://download.oracle.com/javase/6/docs/api/java/net/ServerSocket.html
But there are several problems: Theres a lot of overhead that you need to do yourself. Parse the HTTP request, extract the headers and the body and depending on the headers you need to do certain things like caching, authentication, etc. And that's a lot of stuff you need to implement. Using an existing web server is usually a better idea, since the people who wrote it (usually) know exactly what they are doing.
Another option is the Apache HttpCore library (http://hc.apache.org/httpcomponents-core-ga/index.html). You can use it to write your own Http Server... But again, there's still a lot of stuff you need to take care of ...
If you want to do it for learning purposes, go ahead and implement it yourself. When it is for production, stick with the commonly used web servers.

Send http headers from servlet to app in another environment

I need to send a request from a servlet to an application running in other environment (IIS) with certain information in custom headers.
I know redirecting doesn't send the headers and getServletContext().getRequestDispatcher(url) is to be used in the servlet's context only. Has anybody made this work in some other way? I was thinking in using HttpURLConnection, but would it finally redirect the browser to the targeted app ?
Thanks in advance

You can't redirect from your servlet to the external server and keep the headers, and you can't forward the incoming request to other context.
What you could do, is to use the HttpURLConnection (or other http client library such as HTTPClient) to make the request (with the custom headers you need) to the remote server and, once the operation is complete, redirect the user to the external site (customm headers are not set in this redirection).
This is a little tricky, if you elaborate your question (what do you really need to do) we can probably think about other alternatives.

AJAX? You can send some JavaScript code to the browser which sends a request to the ISS and handle (shows) its answer. It's possible to set http headers with XMLHttpRequest but it needs client side JavaScript coding and you have to find a way to send cross domain requests.

Debug tool for creating and sending HTTP messages (e.g. Curl)

I am developing a software which will be communicating with a server using HTTP (but it is not a web browser). Since the server part is not ready yet, I would like to debug my client software by sending HTTP messages to it. I know that I can send HTTP requests using Curl. But I am not sure if that is sufficient here.
I'm imagining an environment where I send a request from my application, check that it is correct using Wireshark and then reply to the request using some software. Using Curl, I think I would have open a listening port..?

I'd use a simple node.js server for this. You can write your own HTTP server in a few lines of code an simulate various return codes, response headers or response entities easily: http://nodejs.org/
PS: There are proxies that simply print out the HTTP messages. This might be helpful for you too, because you don't have to deal with WireShark anymore just for HTTP-level logging.

You can't do that with cURL. It is an http client, not a server.
The simplest way to do this is to actually implement a mock server application that just returns a static (i.e. hardcoded) message every time. You can do this using any server-side language you like (php, python, ruby, ...), or, you can even do it without a server side language, using just static files served by a webserver such as apache or nginx.
For example, if the server part (the API) would respond to /articles.json with something relevant (a JSON object containing some articles), you could put a file named articles.json that contains some hand-written data in your server's root. Then, your application would think it's calling an API when it's actually just downloading a static file.

You can use firebug addon of firefox browser to see content of HTTP request/response.
It does't require any server (but of course, if you dont have server which process requests from browser and send responses to browser, you 'll always see response "unable to connect").
If you still need to mock response, you can create simple server which is able to respond with mock responses, for example java servlet at tomcat server, with code like this:
public class MyMockServlet extends HttpServlet {
..
private String mockHeaders = "...";
private String mockResponse = "my response";
public void service(HttpRequest request, HttpResponse response){
setHeaderAndBodyInResponse(response);//your method
}
}