Spring Connect Charlotte Event Driven Systems with Spring Boot, Spring Cloud Streams and Kafka Speakers: Rohini Rajaram & Mayuresh Krishna

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5. Events As
Continuous Streams
Business
Transactions
Future Of Data
Stored As Events
Reconstruct A
Shopping Cart
Shopping Cart
Time Constrained
State Store
Future Of Data

13. Publish & Subscribe To
Events
Store Events Process & Analyze Events

18. Relational Data Store
Stream Processing
Capture Transactions
Real Time Aggregations
Publish Results

23. Properties config = new Properties();
config.put(StreamsConfig.APPLICATION_ID_CONFIG, "streams-starter-app");
config.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "server-lb:9092");
config.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG,
Serdes.String().getClass());
config.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG,
Serdes.String().getClass());
KStreamBuilder builder = new KStreamBuilder();
KStream<String, String> kStream = builder.stream("input-topic-name");
// do stuff
kStream.to("word-count-output");
KafkaStreams streams = new KafkaStreams(builder, config);
streams.start();
// Do aggregation making the word as the key and count as the value
// shutdown hook to correctly close the streams application
Runtime.getRuntime().addShutdownHook(new Thread(streams::close));

24. 0 1 2 3 4 5 6 7 8 9
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
P0
P1
P2
Writes
Topic Logs

25. spring.cloud.stream.kafka.binder.brokers=<Broker LB>
spring.cloud.stream.kafka.streams.binder.configuration.default.key.serde=or
g.apache.kafka.common.serialization.Serdes$StringSerde
spring.cloud.stream.kafka.streams.binder.configuration.default.value.serde
=org.apache.kafka.common.serialization.Serdes$StringSerde
spring.cloud.stream.bindings.input.destination=input-topic-name
@StreamListener
@SendTo (Binding.OUTPUT)
public KStream<String, Integer> wordCountProcessing (
@Input (Binding.INPUT) KStream<String, String> wordStream)
{
}

26. Maven Dependency:
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-stream-binder-kafka</artifactId>
</dependency>
Code:
/**
* Constructor with bindings to the output channel for the order topic
* @param binding
*/
public OrderService(ResourceBinding binding) {
this.orderOut = binding.orderOut();
}
public String createOrder(OrderDTO orderDTO)
{
orderOut.send(MessageBuilder.withPayload(order).setHeader("kafka_message
Key", order.getOrderID()).build());

29. Topic A Partition 0
Topic A Partition 0
Producer Consumer

33. lineItemStream = orderEventStream
.filter((key, value) -> value.getState().equals(State.placed))
.flatMapValues(value -> value.getLineItems())
.selectKey((orderId, lineItem) -> lineItem.getSku().toString())
.join(inventoryStream, new KeyValueMapper<String, LineItem, String>() {
@Override
public String apply(String key, LineItem value) {
log.info("Sku Key " + key.toString());
return key;
}
}, new ValueJoiner<LineItem, Inventory, LineItem>() {
@Override
public LineItem apply(LineItem value1, Inventory value2) {
if (value2.getQuantity() > 0) {
value1.setState(LineItemState.validated);
} else {
value1.setState(LineItemState.insufficient_inventory);
}
return value1;
}
});

36. Name Account Balance
Alice $100
Bob $200
Domain Event
Alice gives Bob $50
Bob give Alice $100
Name Account Balance
Alice $150
Bob $150
Change Log Event Stream
Alice’s Acct. Balance is $50
Bob’s Acct. Balance is $250
Alice’s Acct. Balance is $150
Bob’s Acct Balance is $150
Current State

37. https://spring.io/guides/gs/spring-cloud-stream/
https://www.confluent.io/designing-event-driven-systems
https://www.youtube.com/watch?v=P0SEOL_AGro&t=493s