textlines | simple web app to generate a DXF block

You defined the value deserializer to be that for Long, but it looks like your data is a String instead.

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You could adapt this official Confluent Example to your use case. The example is very similar to what you are asking.

To explain this further, you need to create a stream application in which you read data from the topic into a KStream. You haven't provided information about your key. In the Confluent example, records are repartitioned explicitly using map() method, creating a new KeyValue instance for each record (you could do something like using amount as key). Then events are grouped by key and counted.

Is my GenKeyIdProps interface specifying the props need to be part of an object?

Yes, you've defined GenKeyIdProps as an object. All interface definitions are objects. Your GenKeyIdProps is roughly equivalent to:

You are not locking anything, so clone on the UI thread is executed at the same time as remove/add on the other thread. The code could be run in any order. This is bad, because you could cloning an array list that is in the middle of removing an element - in an intermediate, invalid state. When you try to iterate on that incorrectly cloned object, the iterator is confused and thinks you are modifying it concurrently.

In short, ArrayList is not thread safe. It does not make any guarantees. You seem to understand that joinToString isn't thread safe. Well, clone isn't either, and neither is add or remove.

To illustrate how this can happen, let's assume you're using OpenJDK 11. The ArrayList.remove method, among other things, decrease the size field:

You use streams from template documents (templatePDDocument, fontTemplatePdf) created anew and also given free for garbage collection in each loop iteration. Thus, some of these template documents may have been finalized by garbage collection before you call outPDDocument.save, causing the errors you observe.

If you keep this base architecture, you can prevent that those template documents are finalized prematurely by adding them all to some collection and clearing that collection only after calling outPDDocument.save.

Alternatively you can switch to cloning the template pages and using the clones instead of using the original template pages.

Since your question is lacking detail it is difficult to answer. There are different possibilities to verify that your content was added:

1. Extract the text from the PDF and check whether your text is in there

You could group by the given keys and map along roles.

you should write this in your TextView :

android:gravity="start" or android:gravity="start|center"

Groupby works with windowing which is by default 1 day. So, to restream on another topic, the window needs to be closed. Therefore, closing the window is the solution or setting a low window size that would be closed in running the application.

I have solved the problem by closing the stream.