NiFi: Understanding Core FlowFile Attributes: Accessing fileSize and filename in NiFi

I don't know of any out of box functionality to get file size. You can use the execute script to and script up way to easily grab the file size. Or build a processor to grab content size. Here is what the code for the processor would look like. very simple.

@Override
public void onTrigger(final ProcessContext context, final ProcessSession session) throws ProcessException {
final ComponentLog log = getLogger();
final AtomicReference<String> value = new AtomicReference<>();

FlowFile flowfile = session.get();

session.read(flowfile, new InputStreamCallback() {
@Override
public void process(InputStream in) throws IOException {
try{

String outputHandler = context.getProperty(OUTPUTHANDLER).getValue();


String stringToTest = IOUtils.toString(in);

// Check length, in characters if that is what you want
System.out.println(stringToTest.length()); // prints "11"

// Or provided specific encoded sizes ie UTF-8. this can be property driven
//String result = stringToTest.getBytes("UTF-8").toString();

value.set(result);
}catch(Exception ex){
ex.printStackTrace();