Implement Spring Service to send message to different Kafka topics based on configuration

Question

I would like to use Spring Services in order to send data to different Kafka messages based on configuration:

ResponseFactory processingPeply = null;

        switch(endpointType)
        {
            case "email":
                ProducerRecord<String, Object> record = new ProducerRecord<>("tp-email.request", tf);
                RequestReplyFuture<String, Object, Object> replyFuture = processingTransactionEmailReplyKafkaTemplate.sendAndReceive(record);
                SendResult<String, Object> sendResult = replyFuture.getSendFuture().get(10, TimeUnit.SECONDS);
                ConsumerRecord<String, Object> consumerRecord = replyFuture.get(10, TimeUnit.SECONDS);

                processingPeply = (ResponseFactory) consumerRecord.value();
              break;
            case "sms":
                ProducerRecord<String, Object> record = new ProducerRecord<>("tp-sms.request", tf);
                RequestReplyFuture<String, Object, Object> replyFuture = processingTransactionSmsReplyKafkaTemplate.sendAndReceive(record);
                SendResult<String, Object> sendResult = replyFuture.getSendFuture().get(10, TimeUnit.SECONDS);
                ConsumerRecord<String, Object> consumerRecord = replyFuture.get(10, TimeUnit.SECONDS);

                processingPeply = (ResponseFactory) consumerRecord.value();
              break;
            case "network":
                ProducerRecord<String, Object> record = new ProducerRecord<>("tp-network.request", tf);
                RequestReplyFuture<String, Object, Object> replyFuture = processingTransactionNetworkReplyKafkaTemplate.sendAndReceive(record);
                SendResult<String, Object> sendResult = replyFuture.getSendFuture().get(10, TimeUnit.SECONDS);
                ConsumerRecord<String, Object> consumerRecord = replyFuture.get(10, TimeUnit.SECONDS);

                processingPeply = (ResponseFactory) consumerRecord.value();
              break;
              
            default:
                processingPeply = ResponseFactory.builder().status("error").build();
        } 

I currently get:

• Variable 'record' is already defined in the scope
• Variable 'sendResult' is already defined in the scope
• Variable 'consumerRecord' is already defined in the scope

Do you know how I can redesign the code in some better way so I can solve the issue? I would like to use DRY principle with Spring Service in order to reduce the code.

Answer 1

I think you can use interfaces to separate logic of sending data to different endpoints. Take a look to code below:

Main class that sends data and receive Response. It doesn't know anything about email, SMS, network senders.

package com.example.demo.service;

import com.example.demo.dto.Response;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class KafkaSender {

    private final List<EndpointSender> senders;

    public KafkaSender(List<EndpointSender> senders) {
        this.senders = senders;
    }

    public Response send(Object data, String endpoint) {
        return senders
            .stream()
            .filter(it -> it.supports(endpoint))
            .findAny()
            .map(it -> it.send(data))
            .orElseGet(() -> new Response("error"));
    }
}

Then we create interface like this:

package com.example.demo.service;

import com.example.demo.dto.Response;

public interface EndpointSender {
    Response send(Object obj);
    boolean supports(String endpoint);
}

And implementations:

Base class to reduce boilplate code:

package com.example.demo.service.sender;

import com.example.demo.dto.Response;
import com.example.demo.service.EndpointSender;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.producer.ProducerRecord;
import org.springframework.kafka.requestreply.ReplyingKafkaTemplate;
import org.springframework.kafka.requestreply.RequestReplyFuture;
import org.springframework.kafka.support.SendResult;

import java.util.concurrent.TimeUnit;

public abstract class BaseSender implements EndpointSender {

    public abstract ProducerRecord<String, Object> getRecord(Object obj);

    public abstract ReplyingKafkaTemplate<String, Object, Object> kafkaTemplate();

    @Override
    public Response send(Object obj) {
        try {
            RequestReplyFuture<String, Object, Object> replyFuture = kafkaTemplate().sendAndReceive(getRecord(obj));
            SendResult<String, Object> sendResult = replyFuture.getSendFuture().get(10, TimeUnit.SECONDS);
            ConsumerRecord<String, Object> consumerRecord = replyFuture.get(10, TimeUnit.SECONDS);

            return (Response) consumerRecord.value();
        } catch (Throwable t) {
            throw new RuntimeException(t);
        }
    }
}

And implementations for senders: Email sender:

package com.example.demo.service.sender;

import org.apache.kafka.clients.producer.ProducerRecord;
import org.springframework.kafka.requestreply.ReplyingKafkaTemplate;
import org.springframework.stereotype.Service;

@Service
public class EmailSender extends BaseSender {

    private final ReplyingKafkaTemplate<String, Object, Object> processingTransactionEmailReplyKafkaTemplate;

    public EmailSender(ReplyingKafkaTemplate<String, Object, Object> processingTransactionEmailReplyKafkaTemplate) {
        this.processingTransactionEmailReplyKafkaTemplate = processingTransactionEmailReplyKafkaTemplate;
    }

    @Override
    public boolean supports(String endpoint) {
        return "email".equals(endpoint);
    }

    @Override
    public ProducerRecord<String, Object> getRecord(Object obj) {
        return new ProducerRecord<>("tp-email.request", obj);
    }

    @Override
    public ReplyingKafkaTemplate<String, Object, Object> kafkaTemplate() {
        return processingTransactionEmailReplyKafkaTemplate;
    }
}

Sms sender:

package com.example.demo.service.sender;

import org.apache.kafka.clients.producer.ProducerRecord;
import org.springframework.kafka.requestreply.ReplyingKafkaTemplate;
import org.springframework.stereotype.Service;

@Service
public class SmsSender extends BaseSender{

    private final ReplyingKafkaTemplate<String, Object, Object> processingTransactionSmsReplyKafkaTemplate;

    public SmsSender(ReplyingKafkaTemplate<String, Object, Object> processingTransactionSmsReplyKafkaTemplate) {
        this.processingTransactionSmsReplyKafkaTemplate = processingTransactionSmsReplyKafkaTemplate;
    }

    @Override
    public boolean supports(String endpoint) {
        return "sms".equals(endpoint);
    }

    @Override
    public ProducerRecord<String, Object> getRecord(Object obj) {
        return new ProducerRecord<>("tp-sms.request", obj);
    }

    @Override
    public ReplyingKafkaTemplate<String, Object, Object> kafkaTemplate() {
        return processingTransactionSmsReplyKafkaTemplate;
    }
}

Network sender:

package com.example.demo.service.sender;

import org.apache.kafka.clients.producer.ProducerRecord;
import org.springframework.kafka.requestreply.ReplyingKafkaTemplate;
import org.springframework.stereotype.Service;

@Service
public class NetworkSender extends BaseSender{

    private final ReplyingKafkaTemplate<String, Object, Object> processingTransactionNetworkReplyKafkaTemplate;

    public NetworkSender(ReplyingKafkaTemplate<String, Object, Object> processingTransactionNetworkReplyKafkaTemplate) {
        this.processingTransactionNetworkReplyKafkaTemplate = processingTransactionNetworkReplyKafkaTemplate;
    }

    @Override
    public boolean supports(String endpoint) {
        return "network".equals(endpoint);
    }

    @Override
    public ProducerRecord<String, Object> getRecord(Object obj) {
        return new ProducerRecord<>("tp-network.request", obj);
    }

    @Override
    public ReplyingKafkaTemplate<String, Object, Object> kafkaTemplate() {
        return processingTransactionNetworkReplyKafkaTemplate;
    }
}

Answer 2

Applying KISS but not so DRY... Put each code blocks from each case into brackets

case "email": {
...
}
break;
...

By doing this you reducing the case's scopes then you can reuse the same variable names.

Answer 3

You could autowire all the ReplyingKafkaTemplate and look up the one matching your endpoint type.

@Autowired
private List<ReplyingKafkaTemplate<String, Object, Object>> templates;

ReplyingKafkaTemplate<String, Object, Object> template = null;
for(ReplyingKafkaTemplate<String, Object, Object> replyingKafkaTemplate :  templates) {
    String defaultTopic = replyingKafkaTemplate.getDefaultTopic();
    if (defaultTopic.contains(endpointType)) {
        template = replyingKafkaTemplate;
        break;
    }
}
ProducerRecord<String, Object> record = new ProducerRecord<>(template.getDefaultTopic(), tf);
RequestReplyFuture<String, Object, Object> replyFuture = template.sendAndReceive(record);
SendResult<String, Object> sendResult = replyFuture.getSendFuture().get(10, TimeUnit.SECONDS);
ConsumerRecord<String, Object> consumerRecord = replyFuture.get(10, TimeUnit.SECONDS);
ResponseFactory processingPeply = (ResponseFactory) consumerRecord.value();

You could also set up your configuration in such a way to create a bean of look up types followed by injecting Map<String, ReplyingKafkaTemplate> for easy look up. Since I don't know your set up I can't provide the configuration set up for you.

@Autowired
private Map<String, ReplyingKafkaTemplate<String, Object, Object>>> templates;

ReplyingKafkaTemplate<String, Object, Object> template = templates.get(endpointType);
ProducerRecord<String, Object> record = new ProducerRecord<>(template.getDefaultTopic(), tf);
RequestReplyFuture<String, Object, Object> replyFuture = template.sendAndReceive(record);
SendResult<String, Object> sendResult = replyFuture.getSendFuture().get(10, TimeUnit.SECONDS);
ConsumerRecord<String, Object> consumerRecord = replyFuture.get(10, TimeUnit.SECONDS);
ResponseFactory processingPeply = (ResponseFactory) consumerRecord.value();