Apache Kafka从代码创建主题

Question

As we know Topic creation in Kafka should be handled on the the server initialization part. There we use the default script ./kafka-topics --zookeeper ... , but what if we need to create a topic dynamically?

Answer 1

Fortunately, Kafka 0.10.1.0 brought us this ability. I saw these fascinating feature on the Confluence Jira board but couldn't find any documentation related to the topic, irony, isn't it?

So, I went to the source code and found the way of creating topics on the fly. Hopefully it will be helpful for some of you. Of course, if you have a better solution, please, do not hesitate to share it with us.

Ok, let's start.

/** The method propagate topics **/
public List<String> propagateTopics(int partitions, short replication, int timeout) throws IOException {
    CreateTopicsRequest.TopicDetails topicDetails = new CreateTopicsRequest.TopicDetails(partitions, replication);
    Map<String, CreateTopicsRequest.TopicDetails> topicConfig = mTopics.stream()
            .collect(Collectors.toMap(k -> k, v -> topicDetails)); // 1

    CreateTopicsRequest request = new CreateTopicsRequest(topicConfig, timeout); // 2

    try {
        CreateTopicsResponse response = createTopic(request, BOOTSTRAP_SERVERS_CONFIG); // 3
        return response.errors().entrySet().stream()
                .filter(error -> error.getValue() == Errors.NONE)
                .map(Map.Entry::getKey)
                .collect(Collectors.toList()); // 4
    } catch (IOException e) {
        log.error(e);
    }

    return null;
}

1 we need an instance of TopicDetails , for simplicity, I'll share the same configs among all topics. Assume, that mTopics is your list of Strings of all topics you want to create.

2 Basically we want to send a request to our Kafka cluster, now we have the special class for that, - that accepts CreateTopicsRequest and timeout

3 Than we need to send the request and get the CreateTopicsResponse

    private static final short apiKey = ApiKeys.CREATE_TOPICS.id;
    private static final short version = 0;
    private static final short correlationId = -1;

private static CreateTopicsResponse createTopic(CreateTopicsRequest request, String client) throws IllegalArgumentException, IOException {
        String[] comp = client.split(":");
        if (comp.length != 2) {
            throw new IllegalArgumentException("Wrong client directive");
        }
        String address = comp[0];
        int port = Integer.parseInt(comp[1]);

        RequestHeader header = new RequestHeader(apiKey, version, client, correlationId);
        ByteBuffer buffer = ByteBuffer.allocate(header.sizeOf() + request.sizeOf());
        header.writeTo(buffer);
        request.writeTo(buffer);

        byte byteBuf[] = buffer.array();

        byte[] resp = requestAndReceive(byteBuf, address, port);
        ByteBuffer respBuffer = ByteBuffer.wrap(resp);
        ResponseHeader.parse(respBuffer);

        return CreateTopicsResponse.parse(respBuffer);
    }

    private static byte[] requestAndReceive(byte[] buffer, String address, int port) throws IOException {
        try(Socket socket = new Socket(address, port);
            DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
            DataInputStream dis = new DataInputStream(socket.getInputStream())
        ) {
            dos.writeInt(buffer.length);
            dos.write(buffer);
            dos.flush();

            byte resp[] = new byte[dis.readInt()];
            dis.readFully(resp);

            return resp;
        } catch (IOException e) {
            log.error(e);
        }

        return new byte[0];
    }

Here is no magic at all, just sending the request, and than parsing the byte stream to the response.

4 CreateTopicsResponse has property errors , which is just a Map<String, Errors> where key is the topic name you requested. The tricky thing, it contains all topics you requested, but those with no errors has value Errors.None , that's why I'm filtering the response and return only successfully created topics.

Answer 2

Extending Andrei Nechaev answers

With 10.2.0, the way to get an instance of CreateTopicsRequest has changed a bit. We need to use the Builder inner class to build a CreateTopicsRequest instance. Here is a code sample.

CreateTopicsRequest.Builder builder = new CreateTopicsRequest.Builder(topicConfig, timeout, false);
CreateTopicsRequest request = builder.build();