Today Heroku announced that Java is now supported on the Heroku Cloud Application Platform! This is incredibly exciting news and I’m very lucky to be a Heroku for Java Developer Evangelist!

Joining salesforce.com and jumping into the the Java Cloud space holds some nostalgia for me. When I began using Java in 1997 I was working at an ISP in Denver. We did the regular web hosting thing, but when the first Java Servlet engines (like Java Web Server 1.0) came out, I created the “wantjava.com” hosting service. Things were really nasty at first. We could only run one instance of the JWS on a server so I came up with a really bad way to do “multi-tenancy”. I setup a cron job to rsync the customers’ .class files into the server’s webapp and then restart the server. Customers had to email me to get a servlet added to the web.xml file. Uggg… I feel like I need to go to confession for this. But it worked and as the Servlet containers improved we quickly migrated to a more sustainable model.

Now thirteen years later I am privileged to once again be part of Java on the Cloud. But this time around things are so much easier, better, and sexier! Heroku is a leading the way in a new generation of application deployment that is making things much better for us Java developers.

What is Heroku?

Shortly I will dive into how you can run Java on Heroku, but first, what is Heroku? From my perspective, Heroku is a Polyglot Cloud Application Platform. Heroku provides us a way to run Ruby, Node.js, Clojure, and Java applications on a managed, scalable, and multi-tenant system. Heroku also provides numerous add-ons that help us make the shift from monolithic middleware to Cloud Components. Another way to say it is:

Heroku = Polyglot + Platform as a Service (PaaS) + Cloud Components

It is very exciting to see these three things coming together! With Polyglot I can choose the right tool for the job. With PaaS I don’t have to think about managing operating systems, scalability, failover, etc. And with the Cloud Component Architecture I can keep my app thin and focused on what is unique to the problem it needs to solve. Heroku brings these models together as a cloud application platform.

Running Java Apps on Heroku

Heroku can run any Java app that runs in OpenJDK 6. Today Heroku uses Maven to create a “slug” for Java apps. That slug can then be loaded onto one or more “dynos“. You can tell a dyno to execute / start a Java app from the command line and you can also use a “Procfile” to provide a command that will auto-start for each instance of a specific dyno type. Web dynos are able to listen on a port and will receive HTTP traffic through a load balancer that is automatically setup for each app. With that background knowledge, lets dive into code!

For Dreamforce 2011, I (with the help of a few co-workers) put together a Heroku for Java Workbook. The Workbook provides detailed instructions on how to create web apps, connect to a database, setup worker processes, use the Redis to Go Heroku add-on, and use Spring Roo on Heroku. But if you are anxious to get started and don’t need as much hand-holding, here is a quick and very simple walk through of how to run Java on Heroku:

1. Install the heroku command line client on Linux, Mac, or Windows.
2. Install git and setup your ssh key
3. Install Maven
4. Login to Heroku from the command line:

   heroku auth:login

   
   
5. Create a new project directory and move into it:

   mkdir helloherokujava
   cd helloherokujava

6. Create a Maven build file named pom.xml containing:

   <?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>foo</groupId>
       <version>1.0-SNAPSHOT</version>
       <name>helloherokujava</name>
       <artifactId>helloherokujava</artifactId>
   </project>

7. Create a Java source directory:

   mkdir -p src/main/java

8. Create a new Java class in the src/main/java directory named Hello.java containing:

   public class Hello
   {
     public static void main(String[] args)
     {
       System.out.println("hello, world");
     }
   }

9. Compile the class:

   mvn compile

   
   
10. Run the class locally:

    java -cp target/classes Hello

11. Create a local git repo, add the pom.xml file & src dir, and commit the files:

    git init
    git add pom.xml src
    git commit -m init

12. Create a new app on Heroku using the Cedar stack:

    heroku create -s cedar

13. Upload your app to Heroku:

    git push heroku master

    Heroku will create a slug for your app.

14. Run the app on Heroku:

    heroku run "java -cp target/classes Hello"

    Heroku will start a new dyno with your slug and then run the specified command.

You just ran Java on the cloud! Obviously this is a very simple example. But I like to start new things with the simplest thing that could possibly work. Now that you have that working there is more to learn and much more power to harness!

Next Steps

• Go through the Heroku for Java Workbook
• Go through the articles on the Heroku Dev Center
• Ask questions about Heroku on StackOverflow
• Keep watching here for many more blogs about Java on Heroku

Have fun and please let me know if you have any questions about Heroku.

From http://www.jamesward.com/2011/08/25/heroku-adds-java-support