“tiny-router” is Kafka consumer’s message dispatcher
What is “tiny-router” ?
It’s a maven library. It helps to dispatch various types of Kafka messages in the kafka consumer to appropriate message handler.
It can be added to the Kafka producer and consumer component by defining maven dependency as follows.
<dependency>
<groupId>io.github.partha-sen</groupId>
<artifactId>tiny-router</artifactId>
<version>1.0.0</version>
</dependency>What is the need of it?
Little Background …
Sync microservice state change to monolith.
One obvious challenge of application transformation from monolith to microservice with incremental migration release is synchronizing the systems together.
If we enforce all write operations only with newly build microservice but still some read is happening from monolith then you should publish state change events to asynchronous system and further process it to update state of monolith application.
The advantage of doing it asynchronously is to optimize performance and enable loose coupling of monolith API call. When system gets mature and completely replace monolith we just stop processing events. We don’t have to remove any dead code related to Legacy API call in our microservices.
How many “topic” you should create to update legacy application?
It depends on the system design. We can group all logically related operations and then for each group define a topic. In our case we have defined very few Kafka topic - each topic handling multiple type of messages and operations.
Example: All user profile related operation are defined on only one topic and it handles operation like “update address” and “update contact” etc and payload for address and contact are different.
Challenges with multiple types of message processing in single Kafka consumer are-
- Defining message format to accommodate all types of messages and operations.
- Handle message serialization and deserialization.
- Message conversion to the java target Type.
- Delegate message to the appropriate handler to process the message.
How “tiny-router” works?
“tiny-router” first prepares routeMap by processing @RouteEntry annotation, which is defined in message Handler Class.
Code snippet of routeMap and RouteData
private final Map<String, RouteData<T>> routeMap = new HashMap<>();
public class RouteData<T> {
T instance;
Method method;
Class<?> parameterType;
}Define message format to accommodate all type of messages and operation.
a) Message format to accommodate all type of messages and operation.
“tiny-router” defines generic message structure to support multiple operation and payload as below
public class MessageEnvelop<P> {
String action;
String version;
P payload;
}Action field represent Operation.
Example: “Register Product” or “Place Order” or “Update Address” etc.
Version field represent payload version.
This Is optional filed. Example: “v1” or “v2” etc.
Payload field represent message data, It is any Java DTO object.
Example: “Address” or “Product” or “Order” etc.
b) What message Kafka consumer will receive?
Same message what we have sent - only difference is payload is encoded as json String.
public class MessageEnvelop<String> {
String action;
String version;
String payload;
}Message serialization and deserialization.
When we send MessageEnvelop<?> to Kafka topic we must use “com.tiny.router.serialization.MessageEnvelopSerializer” to serialize Kafka message to byte array.
Now when you receive message from kafka topic you should use “com.tiny.router.serialization.MessageEnvelopDeserializer” to deserialize to MessageEnvelop<String>
Message conversion to the java target Type.
As mentioned earlier RouteMap has information of method argument object Type. Using Jackson ObjectMapper “tiny-router” convert payload json string to target Object.
Message delegation to the appropriate handler to process the message.
When any routing path entry is present in the RouteData, “tiny-router” use java reflection to call target Method and hence Message is properly dispatched.