Sydney Java Meet-Up #12

Reactive Programming in Java!

https://www.meetup.com/sydney-java/events/290471569/

Program

6pm - Networking/Drinks/Food
6:30pm - Event Intro and Job Shouts
6:35pm - Reactive Coding in Java
Presenting reactive programming as a paradigm using Java and going through the advantages, use cases and example implementation. by Dana Dabbagh + Reynaldo Rojas, Technical Leads @ Lexicon
7:05pm - 25 minute break
7:30pm - Intro to the Reactive MongoDB Java Driver
A quick tour of what you can do with MongoDB's reactive driver. Building a microservice with JAX-RS async and reactive Mongo.
8pm Event Finish

Intro

Program

Quick acknowledgement of:

• MongoDB for hosting us!

Ethos, vibe

• openness
• inclusiveness
• learning through code, the meetup is organised by coders for coders, with a focus on practical skills and real experiences
• no experts, we're a community of peers all learning together
• supportiveness, we're here for each other

Job Shouts

“Before we get into the tech talks, are there any job shoutouts?”

Talks

Reactive Coding in Java

Over to Dana and Reynaldo!

Intro to the Reactive Java Driver for MongoDB

Why use Reactive to access a database?

Creating Hello World Java 19

IntelliJ -> New Project

• Java 19
• Maven
• Group ID and Artifact ID

Basic POM - Always Add Unit Tests!

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.mycodefu</groupId>
  <artifactId>mongo-reactive</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>mongo-reactive</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>19</maven.compiler.source>
    <maven.compiler.target>19</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.13.2</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>

Driver

https://www.mongodb.com/docs/drivers/reactive-streams/
https://github.com/mongodb/mongo-java-driver/tree/master/driver-reactive-streams

Add Mongo Driver:

<dependency>
    <groupId>org.mongodb</groupId>
    <artifactId>mongodb-driver-reactivestreams</artifactId>
    <version>4.8.0</version>
</dependency>

Note: Comes with a transitive dependency on Project Reactor - you can use the awesome APIs to abstract away the cumbersome Publisher/Subscriber interfaces. https://github.com/reactor/reactor-core

<dependency>
    <groupId>io.projectreactor</groupId>
    <artifactId>reactor-core</artifactId>
    <version>3.5.0</version>
</dependency>

e.g. read from the cursor in batches

package com.mycodefu;

import com.github.javafaker.Faker;
import com.mongodb.client.result.DeleteResult;
import com.mongodb.client.result.InsertManyResult;
import com.mongodb.reactivestreams.client.MongoClient;
import com.mongodb.reactivestreams.client.MongoClients;
import com.mongodb.reactivestreams.client.MongoCollection;
import org.bson.BsonDocument;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.util.List;
import java.util.Objects;

public class Main {
    public static void main(String[] args) {
        MongoClient mongoClient = MongoClients.create();
        MongoCollection<Person> collection = mongoClient.getDatabase("test").getCollection("people", Person.class);

        DeleteResult deleteResult = Mono.from(collection.deleteMany(new BsonDocument())).block();
        assert(Objects.requireNonNull(deleteResult).wasAcknowledged());

        List<Person> people = Flux.range(0, 101).map(i -> new Person(Faker.instance().name().fullName())).collectList().block();
        InsertManyResult result = Mono.from(collection.insertMany(people)).block();
        assert(Objects.requireNonNull(result).wasAcknowledged());

        Flux.from(collection.find()).buffer(20).doOnNext(System.out::println).blockLast();

        System.out.println("Hello Sydney Java Meetup!");
    }
}

You could also use Faker for fun for test data names:

<dependency>
    <groupId>com.github.javafaker</groupId>
    <artifactId>javafaker</artifactId>
    <version>1.0.2</version>
</dependency>

More useful example:
https://github.com/Jett59/reactive-mongo-test