Deserialisasi dan Konversi Pesan
Konfigurasikan deserialiser untuk berbagai format pesan, seperti String, JSON, dan objek khusus, serta tangani konversi pesan di dalam listener Anda.
Deserialisasi dan Konversi Pesan adalah pelajaran Advanced Spring Boot 4: Event-Driven Architecture (Kafka) gratis di CoddyKit. Ini adalah pelajaran 3 dari 4. Kamu bisa membaca pelajaran lengkapnya di bawah secara gratis — lalu praktikkan langsung di browser dengan editor kode bawaan dan tutor AI 24/7. Ini adalah bagian dari jalur belajar Advanced Spring Boot 4: Event-Driven Architecture (Kafka), dan progresmu tersinkronisasi di web dan aplikasi CoddyKit. Kursus Advanced Spring Boot 4: Event-Driven Architecture (Kafka) mencakup 4 pelajaran total.
Bagian dari pelajaran ini belum diterjemahkan dan ditampilkan dalam bahasa Inggris.
Kafka's Raw Messages
Kafka doesn't care about the format of your data. It treats every message as a raw array of bytes. This is how messages are stored and transmitted.
When a producer sends a message, it's first converted into bytes. When a consumer receives that message, it's still just a bunch of bytes.
This flexibility allows Kafka to handle any data type, but it means consumers need a way to interpret those bytes back into a usable format.
From Bytes to Objects: Deserialization
To make sense of Kafka messages in your Java application, you need to convert these raw bytes back into meaningful Java objects. This crucial process is called deserialization.
A deserializer is a specific component that knows how to read a byte array and reconstruct a Java object from it. Think of it as the reverse of serialization.
Without proper deserialization, your consumer would only ever see byte[], which isn't very useful for application logic.
Default String Deserialization
Spring for Apache Kafka provides sensible defaults to get you started quickly. If you don't specify otherwise, it assumes your message keys and values are simple strings.
Behind the scenes, it uses org.apache.kafka.common.serialization.StringDeserializer to convert message bytes into Java String objects.
This works perfectly for plain text messages, but most real-world applications often need to handle more structured data.
Code: Simple String Consumer
Here's a basic Spring Boot application with a Kafka listener that consumes simple string messages. Notice the String type in the listener method signature.
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.stereotype.Component;
@SpringBootApplication
public class SimpleConsumerApp {
public static void main(String[] args) {
SpringApplication.run(SimpleConsumerApp.class, args);
System.out.println("String consumer app started, listening on my-string-topic...");
}
@Component
static class MyStringListener {
@KafkaListener(topics = "my-string-topic", groupId = "string-group")
public void listen(String message) {
System.out.println("Received String: " + message);
}
}
}Configuring Deserializers Explicitly
You can explicitly configure which deserializers to use in your application.properties or application.yml file. This tells Spring Kafka which classes to use for converting bytes for both the message key and value.
spring.kafka.consumer.key-deserializerspring.kafka.consumer.value-deserializer
For our default string example, these would be set to org.apache.kafka.common.serialization.StringDeserializer.
Working with JSON Data
JSON (JavaScript Object Notation) is a widely used format for exchanging structured data. It's very common for Kafka messages to carry data in JSON format.
To utilize JSON messages effectively in your Java application, you need to convert the incoming JSON string (or bytes) into a Java object, typically a Plain Old Java Object (POJO).
This mapping allows you to easily access data fields directly, like myObject.getId() or myObject.getName(), instead of parsing JSON manually.
Spring's JsonDeserializer
Spring for Apache Kafka provides a powerful org.springframework.kafka.support.serializer.JsonDeserializer to simplify handling JSON messages.
This deserializer leverages the popular Jackson library to automatically map incoming JSON bytes to your specified Java POJO class.
You just need to configure it to know which POJO type to expect, and it handles the complex conversion for you.
Code: Defining an Event POJO
First, let's define a simple Java POJO that will represent our incoming JSON data. The properties of this POJO should match the fields in your JSON messages.
package com.coddykit;
// MyEvent.java
public class MyEvent {
private String id;
private String description;
// Default constructor is crucial for deserialization
public MyEvent() {}
public MyEvent(String id, String description) {
this.id = id;
this.description = description;
}
// Getters and Setters (omitted for brevity, but needed)
public String getId() { return id; }
public void setId(String id) { this.id = id; }
public String getDescription() { return description; }
public void setDescription(String description) { this.description = description; }
@Override
public String toString() {
return "MyEvent{id='" + id + "', description='" + description + "'}";
}
}Code: Consuming JSON Messages
Now, let's update our consumer to use the JsonDeserializer and listen for MyEvent objects. Remember, you'll also need to configure the deserializer in your application.properties.
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.stereotype.Component;
import com.coddykit.MyEvent; // Import your POJO
@SpringBootApplication
public class JsonConsumerApp {
public static void main(String[] args) {
SpringApplication.run(JsonConsumerApp.class, args);
System.out.println("JSON consumer app started, listening on my-json-topic...");
}
@Component
static class MyJsonListener {
@KafkaListener(topics = "my-json-topic", groupId = "json-group")
public void listen(MyEvent event) {
System.out.println("Received JSON Event: " + event.toString());
}
}
}
// Required application.properties configuration:
// spring.kafka.consumer.key-deserializer=org.apache.kafka.common.serialization.StringDeserializer
// spring.kafka.consumer.value-deserializer=org.springframework.kafka.support.serializer.JsonDeserializer
// spring.kafka.properties.spring.json.value.default.type=com.coddykit.MyEventDeserializer Configuration Quiz
Consider a Spring Boot Kafka consumer application that needs to process messages where the value is a JSON representation of a Product object, defined in com.example.Product. Which configuration is essential in application.properties for this setup?
Deserialization Recap
Great job! In this lesson, you learned that Kafka messages are raw bytes and require deserialization to be used in Java applications.
- Spring Kafka uses
StringDeserializerby default for simple text messages. - You can configure specific deserializers for keys and values using
application.properties. - The
JsonDeserializersimplifies mapping JSON messages to Java POJOs automatically.
Understanding deserialization is fundamental to building robust Kafka consumers that can handle various data formats effectively.
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- Kursus
- 12
- Pelajaran
- 48
Pertanyaan yang Sering Diajukan
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Apa yang akan aku pelajari di “Deserialisasi dan Konversi Pesan”?
Konfigurasikan deserialiser untuk berbagai format pesan, seperti String, JSON, dan objek khusus, serta tangani konversi pesan di dalam listener Anda. Kamu berlatih Advanced Spring Boot 4: Event-Driven Architecture (Kafka) dengan kode praktik yang langsung kamu jalankan di browser, dan tutor AI 24/7 menjawab pertanyaanmu saat kamu mengerjakan pelajaran ini.
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Semua pelajaran dalam kursus ini
- Membangun Kontainer Listener Kafka
- Manajemen Grup Konsumen
- Deserialisasi dan Konversi Pesan
- Konsumsi Berkelompok dan Mode Pengakuan