Kafka Using Java. Part 2.
Distributed Systems Development A-Z Guide.
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In the previous two articles, we have described Apache Kafka installation into MacOS environment for development purposes.
How to install Apache Kafka on MacOS
Also, we have explained how to use Kafka with Java.
But there is another approach more related to single-time fetch. For example, you want to read the first 5 messages and that’s all. This approach is called Assign and Seek.
We can use the same project from Part 1. Let’s add a new class AssignSeekConsumer.
We will need the same variables except for Group ID.
And constructor is absolutely straightforward. We simply initialize Logger, bootstrap server and a topic.
We initialize properties in the same fashion as in Part 1.
And now the different part. We define the Run method with parameters — messages offset, fetching partition number and number of messages to fetch. Here we initialize a Consumer with props defined above and execute two methods — at first we setup consumer and then fetching messages.
We start to wait and to fetch messages from the selected topic. We do this in a very imperative way just for the sake of clarity. Don’t write such code in production, please. We define a number of messages we have already fetched and it’s 0 on the beginning. Also, we define a flag to stop reading messages when it’s enough. ConsumerRecord is an object, that polls Kafka broker and we read fetched messages in a plain the for loop. Once the number of messages reaches required, we exiting the loop. That’s all.
Let’s define the Main function in the class and read messages we have sent earlier in Part 1. Here 15L means a variable of a Long type. Partition number — is, well, a number of a partition to read. A number of messages — the number of messages we’re going to fetch.
The result should look something like this.
The source code is available in our Github repo:
To know more about Kafka and how to use Kafka with Java, click on links below
Thank you for reading!
