oheger / javamagreact

Example code for JavaMagazin article about reactive programming

JavaMagAkka

This repository contains example code for an article in the German Java Magazin about different reactive programming models.

The article explores the impact of reactive programming on a simple use case: reading a file from the file system. It shows different implementations for this task (blocking and non-blocking) using plain Java and the reactive frameworks Vert.x and Akka.

A multi-module Gradle build is provided to build the whole project. The examples are logically grouped into sub projects.

Plain Java

The plainJava module contains example code that only uses Java and has no external dependencies. Main classes are provided which can be invoked directly. The classes expect a path to a file as command line argument. They read this file and dump the content to the console. The following examples are available:

• BlockingFileReader: A simple blocking implementation to read a file.
• AsyncFileReaderMain: Reads a file asynchronously using the Java nio package.

Vert.x

The vertx module contains examples based on the Vert.x framework. Running these classes is a bit special because they are verticles that have to run under the control of Vert.x. Therefore, the project provides the VertxStartup class which starts the framework and deploys all demo verticles. In addition, it adds the Vert.x Shell, so that interaction from the outside is possible. The verticles register themselves as listeners on the event bus and react on string messages pointing to the files to be read or processed. Via the shell corresponding messages can be sent, for instance:

%bus-send react.file.read /path/to/my/file.txt

The table below lists the demo verticles and the event bus addresses they listen on:

Verticle class	Event bus address	Purpose
ReadFileVerticle	react.file.read	Demonstrates a simple asynchronous file read operation.
ProcessFileVerticleCB	react.file.process	Processes a file in multiple steps using nested callbacks. Shows the downsides of the callback approach.
ProcessFileVerticleFuture	react.file.process.future	Does the same processing as ProcessFileVerticleCB, but uses futures to combine the single steps.

Akka

The single example in this module, is written in Scala and demonstrates file processing using the streaming API offered by Akka. It is an application which can be called directly. It expects two command line arguments for the input file and the output file.