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ExecuteStreamCommand won't read foreign characters

We have Apache Nifi set to write files to local drive, then run program that processes these files and outputs response to "response" attribute. This is a JSON string that we then deliver to API to update records.
However, issue is that while we can successfully write, read and process the files, Nifi fails to understand non-English characters in the response text. This leads to names being corrupted when we send back the response. This only applies to the JSON string we receive from the program.
Nifi is running Windows 10 environment When we run the program manually using files outputted by Nifi, we get correct output. Issue only happens in Nifi.
To provide example, input json is:
{
"player" : "mörkö",
"target" : "goal",
"didhitin" : ""
}
This is stored in our programs work folder and we call program using ExecuteStreamCommand , giving our input JSON file as the parameter. JSON is processed and our program outputs following JSON, which is then stored into response attribute of the flowfile:
{
"player" : "mörkö",
"target" : "goal",
"didhitin" : "true"
}
However, issue is that when this is read by Nifi into the response attribute of the flowfile, it becomes
{
"player" : "m¤rk¤",
"target" : "goal",
"didhitin" : "true"
}
(Not the actual process, but close enough to demonstrate the issue)
Which, when we feed it into API, would either fail or corrupt the name of the original (In this case, value of player). Neither which is desirable output.
So far, we have figured out that this is most likely issue with encoding, but we have not found a way to change the encoding of Nifi to possibly fix incorrectly read characters.

Managed to fix this issue by adding following line to the start of the program:
Console.OutputEncoding = Encoding.UTF8;
This effectively enforces the program to output UTF-8 characters, which would be in-line with rest of the flow.

Sending binary files jpg from android with Json Rest Services

I can't find a way to send binary file jpg with json Rest. The last one that I tried is with Base64.encodeToString(byte[] array, Base64.DEFAULT) and I expected in the server side with Base64.getDecoder().decode(String)... yet no results. I have seen many posts, but nothing has helped. Can you suggest me any way or library.
I am using java with Eclipse. In the client side I use android.util.Base64 library, while in server side I use java.util.Base64.
The error that show me is this:
Unexpected padding character ('=') as character #4 of 4-char base64
unit: padding only legal as 3rd or 4th character; nested exception is
com.fasterxml.jackson.databind.exc.InvalidFormatException: Cannot
deserialize value of type byte[] from String

Java-MySQL-Android: bad base-64

I guess this is a stupid question with an obvious solution, but I don't see it yet. So the problem is: I get an IllegalArgumentException on Android, which says my base64 input is not valid. This input took the following way before:
Upload: PDF file -(Java Base64 encoder) > Java Base64 encoded string -(POST)-> PHP -(INSERT as mediumtext via mysqli query)-> MySQL DB
Download: MySQL record -(SELECT via mysqli query and fetch assoc afterwards)-> PHP vars -(JSON)-> Java as JSON -(Jackson library, maps JSON to object containing String)-> Java Base64 String - (Android Base64 decoder)-> Exception
Is there any failure in my workflow? Communication is done with UTF-8 via HttpUrlConnection.

I was able to solve the problem: During transfer to the server + and / got omitted. After manually replacing them, everything is working now.

WebSocket multipart/form-data emulation possible?

Is there a possibility to send a json text with binary data?
I'am calling it multipart/form-data cause in the html form we can send text with a binary file, how to do the same with the websockets, is that possible?
so here is an example:
var arrayBuffer = new ArrayBuffer();
// lets say here we fill our array buffer with binary data in the browser
// so here we got 2 ways
// 1) First we can send the json text indicating that the next request will be a binary data file
// so using this way the next request will have ready an Id for the uploaded file if we are working
// with database
var obj = {};
obj.somedata = "hello This is a name for my item";
websocket.send(JSON.stringify(obj)); //first sending the text
websocket.send(arrayBuffer); //sending the binary data file
// 2) Second, This is the way I prefer most, but I don't know if this is possible
// we send a json object
var obj = {};
obj.somedata = "hello This is a name for my item";
obj.file = arrayBuffer;
websocket.send(JSON.stringify(obj));
but the problem is that I can't put a binary data into a text json, the binary data gets corrupted this way, in the server side I'am using java... cause using 2 requests for sending a file and the input text data is not a good way I think, any hints?

If server cannot handle binary data (which is maybe problem with configuration or your program, I'm sending binary data this way without no problem), then you can encode your data in base64 or escape them into json. But the best way would be repairing server side...
If you wanna use base64 way, look at this: https://github.com/niklasvh/base64-arraybuffer, and for example this: Base64 Encoding in Java

The Process to Store & Retrieve an Image in a Database

I have never saved and retrieved an image to and from the database before. I wrote down what I guessed would be the process. I would just like to know if this is correct though:
Save image:
Select & Upload image file from jsp (Struts 2) which will save it as a .tmp file.
Convert the .tmp file to a byte[] array (Java Server-Side)
Store the byte[] array as a blob in the database (Java Server-Side)
Get image:
Get the byte[] array from the database (Java Server-Side)
Convert the byte[] array to an image file (Java Server-Side)
Create the file in a location (Java Server-Side)
Use an img tag to display the file (JSP Client-Side)
Delete the file after it's finished being used? (Java Server-Side)
I'm aware of the fact that it is highly recommended to not save & retrieve images to and from the database. I would like to know how to do it anyway.
Thanks

Almost correct.
It's expensive and not so great to create the file on the fly and then delete it.
Yes, you store it as the raw bytes in the database, but the way to retrieve it and display it to a client machine is to implement a web handler that sets the content-type of the response to the appropriate MIME type and then dumps the bytes out to the response stream.

Yes, You get it right.
Save Image :
The decision to save image is very much dependent on further usage. You have one option to save the file on the file system. The location for saved file should be saved into the metadata in the database table.
Get Image:
You do not have to right file data on any temp location. It can be easily rendered from the database only. Just send a request from client and intercept that request in a spacial designed Servlet. This Servlet will read the file metadata and corresponding file, if successful, write the file back on the response stream.