Build Applications on Top of H2O

Start Developing Your Application On Top of H₂O-dev

This tutorial targets developers who are trying to build application on top of the h2o-dev repository. It will walk you through a quick introduction of H₂O droplets - projects templates which can be used to build a new application.

1. Cloning the examples repository

The h2o-droplets repository on GitHub contains some very simple starter projects for different languages. Let's get started by cloning the h2o-droplets repository, and changing to that directory.

$ git clone https://github.com/0xdata/h2o-droplets.git

Cloning into 'h2o-droplets'...
remote: Counting objects: 53, done.
remote: Compressing objects: 100% (33/33), done.
remote: Total 53 (delta 10), reused 39 (delta 0)
Unpacking objects: 100% (53/53), done.
Checking connectivity... done.

$ cd h2o-droplets

Note: if you are using H₂O training sandbox, the repository is already cloned for you in ~/devel/h2o-droplets.

2. A quick look at the repo contents

As of this writing, the repository contains a Java example and a Scala example. Each of these is an independent starter project.

$ ls -al

total 8
drwxr-xr-x   6 tomk  staff   204 Oct 28 08:40 .
drwxr-xr-x  35 tomk  staff  1190 Oct 28 08:40 ..
drwxr-xr-x  13 tomk  staff   442 Oct 28 08:40 .git
-rw-r--r--   1 tomk  staff   322 Oct 28 08:40 README.md
drwxr-xr-x  11 tomk  staff   374 Oct 28 08:40 h2o-java-droplet
drwxr-xr-x  11 tomk  staff   374 Oct 28 08:40 h2o-scala-droplet

Let's take a closer look at the Java example:

$ find h2o-java-droplet -type f

h2o-java-droplet/.gitignore
h2o-java-droplet/build.gradle
h2o-java-droplet/gradle/wrapper/gradle-wrapper.jar
h2o-java-droplet/gradle/wrapper/gradle-wrapper.properties
h2o-java-droplet/gradle.properties
h2o-java-droplet/gradlew
h2o-java-droplet/gradlew.bat
h2o-java-droplet/README.md
h2o-java-droplet/settings.gradle
h2o-java-droplet/src/main/java/water/droplets/H2OJavaDroplet.java
h2o-java-droplet/src/test/java/water/droplets/H2OJavaDropletTest.java

As you can see, the Java example contains of a build.gradle file, a Java source file, and a Java test file.

Look at the build.gradle file and you will see the following sections, which link the Java droplet sample project to a version of h2o-dev published in MavenCentral:

repositories {
    mavenCentral()
}

ext {
  h2oVersion = '0.1.8'
}

dependencies {
    // Define dependency on core of H2O
    compile "ai.h2o:h2o-core:${h2oVersion}"
    // Define dependency on H2O algorithm
    compile "ai.h2o:h2o-algos:${h2oVersion}"
    // Demands web support
    compile "ai.h2o:h2o-web:${h2oVersion}"

    // H2O uses JUnit for testing
    testCompile 'junit:junit:4.11'
}

This is all very standard Gradle stuff. In particular, note that this example depends on three different H₂O artifacts, all of which are built in the h2o-dev repository.

h2o-core contains base platform capabilities like H₂O's in-memory distributed key/value store and mapreduce frameworks (the "water" package).
h2o-algos contains math algorithms like GLM and Random Forest (the "hex" package).
h2o-web contains the browser web UI (lots of javascript).

3. Preparing the example for use in your IDE

Let's walk through an example using IntelliJ IDEA. The first step is to use Gradle to build your IntelliJ project file.

$ cd h2o-java-droplet $ ./gradlew idea

:ideaModule
Download http://repo1.maven.org/maven2/ai/h2o/h2o-core/0.1.8/h2o-core-0.1.8.pom
Download http://repo1.maven.org/maven2/ai/h2o/h2o-algos/0.1.8/h2o-algos-0.1.8.pom
Download http://repo1.maven.org/maven2/ai/h2o/h2o-web/0.1.8/h2o-web-0.1.8.pom
[... many more one-time downloads not shown ...]
:ideaProject
:ideaWorkspace
:idea

BUILD SUCCESSFUL

Total time: 51.429 secs

You will see three new files created with IDEA extensions. The .ipr file is the project file.

$ ls -al

total 168
drwxr-xr-x  15 tomk  staff    510 Oct 28 10:03 .
drwxr-xr-x   6 tomk  staff    204 Oct 28 08:40 ..
-rw-r--r--   1 tomk  staff    273 Oct 28 08:40 .gitignore
drwxr-xr-x   3 tomk  staff    102 Oct 28 10:03 .gradle
-rw-r--r--   1 tomk  staff   1292 Oct 28 08:40 README.md
-rw-r--r--   1 tomk  staff   1409 Oct 28 08:40 build.gradle
drwxr-xr-x   3 tomk  staff    102 Oct 28 08:40 gradle
-rw-r--r--   1 tomk  staff     23 Oct 28 08:40 gradle.properties
-rwxr-xr-x   1 tomk  staff   5080 Oct 28 08:40 gradlew
-rw-r--r--   1 tomk  staff   2404 Oct 28 08:40 gradlew.bat
-rw-r--r--   1 tomk  staff  33316 Oct 28 10:03 h2o-java-droplet.iml
-rw-r--r--   1 tomk  staff   3716 Oct 28 10:03 h2o-java-droplet.ipr
-rw-r--r--   1 tomk  staff   9299 Oct 28 10:03 h2o-java-droplet.iws
-rw-r--r--   1 tomk  staff     39 Oct 28 08:40 settings.gradle
drwxr-xr-x   4 tomk  staff    136 Oct 28 08:40 src