Kafka - Oracle AQ Integration

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An example of a basic Kafka - Oracle Advanced Queuing (AQ) adapter.

Kafka topics used in the example:

1. "to-be-enqueued"

A topic where JSON strings are sent to be enqueued further

3. "dequeued"

A topic where dequeued objects (converted to JSON strings) are displayed.

An order of execution:

1. JSON string is inserted into the "to-be-enqueued" Kafka topic
2. JSON string gets deserialized into a new object
3. The new object is inserted into Oracle queue
4. The object is extracted from Oracle queue
5. The extracted object is serialized into a JSON string
6. JSON string is sent to "dequeued" Kafka topic

The object type stored in Oracle queue:

CREATE TYPE c##user.extended_song AS OBJECT(
	title VARCHAR2(80),
	duration INTEGER,
	file_path VARCHAR2(80),
	description CLOB,
	added_at TIMESTAMP(2)
);

A visual representation of the execution order:

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Source code structure:

src/
├─ main/
│  ├─ java/
│  │  ├─ database/
│  │  │   ├─ QueueManager.java
│  │  │   ├─ QueueSetup.java
│  │  ├─ json/
│  │  │   ├─ ClobFieldDeserializer.java
│  │  │   ├─ ClobFieldSerializer.java
│  │  │   ├─ JsonValidator.java
│  │  ├─ kafka/
│  │  │   ├─ KafkaManager.java
│  │  ├─ main/
│  │  │   ├─ Main.java
│  │  ├─ model/
│  │      ├─ ExtendedSong.java
│  ├─ resources/
│     ├─ ExtendedSongJsonScheme.json
│     ├─ jdbc.properties 
│     ├─ kafka.properties
│     ├─ log4j.properties

• database/QueueManager
  • readJdbcProperties() - reading jdbc.properties resource file and setting JDBC variables
  • establishDatabaseConnection() - getting JDBC connection instance
  • createAqSession() - creating a new AQ Session instance
  • getConnection() - getter method for JDBC connection instance
  • getAqSession() - getter method for AQ session instance
  • setQueue() - setting Oracle queue variable
  • enqueue() - object enqueuing method
  • dequeue() - object dequeuing method
  • queueIsEmpty() - checking if queue table is empty
• database/QueueSetup
  • createQueue()
  • startQueue()
  • stopQueue()
• json/ClobFieldDeserializer - CLOB field deserialization (JSON -> POJO)
  • deserialize()
• json/ClobFieldSerializer - CLOB field serialization (POJO -> JSON)
  • serialize()
• json/JsonValidator
  • validate() - validating JSON string for the Song object
• kafka/KafkaManager
  • readKafkaProperties() - reading kafka.properties and setting Kafka variables
  • getConsumer() - returning Kafka Consumer instance
  • getProducer() - returning Kafka Producer instance
  • startStreaming() - starting Producer while() loop
  • startListening() - starting Consumer while() loop
• main/Main
  • main() - entry point of the app (invokes Enqueuer and Dequeuer threads)
• model/ExtendedSong - the class that represents Oracle object type (Song) by implementing SQLData interface

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Usage:

• Run Zookeeper
• Run Kafka Server
• Edit .properties files (JDBC and Kafka access credentials). Run the app (main.Main)
• Send a new Song as a JSON string to "to-be-enqueued" topic:

{"title":"Haruka Kanata", "duration":165, "filePath": "/etc/music/haruka_kanata.mp3", "description": "Haruka Kanata song description", "addedAt": "2021-11-01 00:33:05.777"}

• The string will be deserialized to POJO Song
• POJO Song will be enqueued and then dequeued:

• Dequeued POJO will be serialized and sent to "dequeued" topic:

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