Spark on Heroku

spark.md

This guide will get you started using Spark on Heroku/Cedar. Spark is basically a clone of Sinatra for Java. 'Nuff said.

Create your app

Create a single Java main class in src/main/java/HelloWorld.java:

import static spark.Spark.*;
import spark.*;

public class HelloWorld {

   public static void main(String[] args) {

      setPort(Integer.parseInt(System.getenv("PORT")));
      get(new Route("/hello") {
         @Override
         public Object handle(Request request, Response response) {
            return "Hello World!";
         }
      });

   }

}

Declare dependencies

Set up your pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<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/maven-v4_0_0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>org.example</groupId>
	<version>1.0-SNAPSHOT</version>
	<artifactId>mysparkapp</artifactId>
	<repositories>
        <repository>
              <id>Spark repository</id>
              <url>http://www.sparkjava.com/nexus/content/repositories/spark/</url>
        </repository>
    </repositories>
    <dependencies>
        <dependency>
              <groupId>spark</groupId>
              <artifactId>spark</artifactId>
              <version>0.9.9.3-SNAPSHOT</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-dependency-plugin</artifactId>
                 <version>2.3</version>
                 <executions>
                     <execution>
                         <phase>package</phase>
                         <goals><goal>copy-dependencies</goal></goals>
                     </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Create a Procfile

Put the launch command in a file called Procfile:

web:    java -cp target/dependency/*:target/classes HelloWorld

Try building it locally (not strictly required for heroku, but nice to try before you commit)

$ mvn clean install

Try running the server

$ foreman start

Check into Git

Add a .gitignore to prevent generated files from being checked in:

$ echo target > .gitignore

Create a git repo and check in your code

$ git init
$ git add .
$ git commit -m init

Create a Heroku app and deploy

Create an app on the Cedar stack:

$ heroku create --stack cedar
$ git push heroku master
Counting objects: 9, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (5/5), done.
Writing objects: 100% (9/9), 1.16 KiB, done.
Total 9 (delta 0), reused 0 (delta 0)

-----> Heroku receiving push
-----> Java app detected
-----> Installing Maven 3.0.3..... done
-----> Installing settings.xml..... done
-----> executing .maven/bin/mvn -B -Duser.home=/tmp/build_brdc75hmaxsu -s .m2/settings.xml -DskipTests=true clean install
       [INFO] Scanning for projects...
       [INFO]                                                                         
       [INFO] ------------------------------------------------------------------------
       [INFO] Building hellospark 1.0-SNAPSHOT
       [INFO] ------------------------------------------------------------------------
       ...
-----> Discovering process types
       Procfile declares types -> web
-----> Compiled slug size is 14.2MB
-----> Launching... done, v3
       http://cold-moon-3783.herokuapp.com deployed to Heroku

Test that it works:

$ curl http://cold-moon-3783.herokuapp.com/hello
Hello World!