#Getting Started with Java 7 on Heroku
- Basic knowledge of Java, including a configured JDK 7 and Maven.
- A Heroku account -- signup is free and instant.
Install the Heroku Toolbelt on your local workstation. This ensures that you have access to the Heroku command-line client, Foreman, and the Git revision control system.
Once installed, you can use the heroku command from your command shell. Log in using the email address and password you used when creating your Heroku account:
$ heroku login
Enter your Heroku credentials.
Email: adam@example.com
Password:
Could not find an existing public key.
Would you like to generate one? [Yn]
Generating new SSH public key.
Uploading ssh public key /Users/adam/.ssh/id_rsa.pub
Press enter at the prompt to upload your existing ssh key or create a new one, used for pushing code later on.
You can run any Java application on Heroku that uses Maven as build tool. As an example, we will write a web app using Jetty. Here is a basic servlet class that also contains a main method to start up the application:
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.*;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.*;
public class HelloWorld extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
resp.getWriter().print("Hello from Java!\n");
}
public static void main(String[] args) throws Exception{
Server server = new Server(Integer.valueOf(System.getenv("PORT")));
ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
context.setContextPath("/");
server.setHandler(context);
context.addServlet(new ServletHolder(new HelloWorld()),"/*");
server.start();
server.join();
}
}Cedar recognizes Java apps by the existence of a pom.xml file. Here's an example pom.xml for the Java/Jetty app we created above.
<?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>com.example</groupId>
<version>1.0-SNAPSHOT</version>
<artifactId>helloworld</artifactId>
<dependencies>
<dependency>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-servlet</artifactId>
<version>7.6.0.v20120127</version>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>2.5</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.4</version>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>package</phase>
<goals><goal>copy-dependencies</goal></goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>Prevent build artifacts from going into revision control by creating this file:
target
Build your app locally:
$ mvn package
As part of the build, Maven gathers dependencies and copies them into the directory target/dependency. Start you app locally by setting the PORT environment variable and running Java with all dependencies on the classpath:
On Mac & Linux:
$ export PORT=5000
$ java -cp target/classes:"target/dependency/*" HelloWorld
(double quotes needed to prevent expansion of *)
On Windows:
$ set PORT=5000
$ java -cp target\classes;"target\dependency\*" HelloWorld
You should now see something similar to:
2012-01-31 15:51:21.811:INFO:oejs.Server:jetty-7.6.0.v20120127
2012-01-31 15:51:21.931:INFO:oejsh.ContextHandler:started o.e.j.s.ServletContextHandler{/,null}
2012-01-31 15:51:21.971:INFO:oejs.AbstractConnector:Started SelectChannelConnector@0.0.0.0:5000
Open the app in your browser:
http://localhost:5000
To run your web process on Heroku, you need to declare what command to use. We'll use Procfile to declare how our web process type is run.
Here's what the Procfile looks like:
web: java -cp target/classes:target/dependency/* HelloWorld
(note: no double quotes needed in Procfile)
##Add system.properties to your app
Create a file in the base directory of your app called system.properties.
Add the property, java.runtime.version=1.7.
Note: Currently, supported versions are 1.6, 1.7, and 1.8. The default is 1.6.
We now have the three major components of our app: build configuration and dependencies in pom.xml, process types in Procfile, and our application source in src/main/java/HelloWorld.java. Let's put it into Git:
$ git init
$ git add .
$ git commit -m "init"
Create the app:
$ heroku create --buildpack https://github.com/heroku/heroku-buildpack-java.git#multijdk
Creating stark-sword-398... done, stack is cedar
http://stark-sword-398.herokuapp.com/ | git@heroku.com:stark-sword-398.git
Git remote heroku added
Deploy your code:
$ git push heroku master
Counting objects: 47, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (25/25), done.
Writing objects: 100% (47/47), 10.25 KiB, done.
Total 47 (delta 19), reused 42 (delta 17)
-----> Heroku receiving push
-----> Fetching custom buildpack... cloning with git...done
-----> Java app detected
-----> Installing OpenJDK 1.7...done
-----> Installing settings.xml... done
-----> executing /app/tmp/repo.git/.cache/.maven/bin/mvn -B -Duser.home=/tmp/build_3k0p14ghrmdzs -Dmaven.repo.local=/app/tmp/repo.git/.cache/.m2/repository -s /app/tmp/repo.git/.cache/.m2/settings.xml -DskipTests=true clean install
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building helloworld 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 10.062s
[INFO] Finished at: Tue Jan 31 23:27:20 UTC 2012
[INFO] Final Memory: 12M/490M
[INFO] ------------------------------------------------------------------------
-----> Discovering process types
Procfile declares types -> web
-----> Compiled slug size is 948K
-----> Launching... done, v3
http://empty-fire-6534.herokuapp.com deployed to Heroku
Now, let's check the state of the app's processes:
$ heroku ps
Process State Command
------- ---------- ------------------------------------
web.1 up for 10s java -cp target/classes:target/dep..
The web process is up. Review the logs for more information:
$ heroku logs
...
2012-01-31T23:27:27+00:00 heroku[web.1]: Starting process with command `java -cp target/classes:target/dependency/* HelloWorld`
2012-01-31T23:27:28+00:00 app[web.1]: 2012-01-31 23:27:28.280:INFO:oejs.Server:jetty-7.6.0.v20120127
2012-01-31T23:27:28+00:00 app[web.1]: 2012-01-31 23:27:28.334:INFO:oejsh.ContextHandler:started o.e.j.s.ServletContextHandler{/,null}
2012-01-31T23:27:28+00:00 app[web.1]: 2012-01-31 23:27:28.373:INFO:oejs.AbstractConnector:Started SelectChannelConnector@0.0.0.0:8236
2012-01-31T23:27:29+00:00 heroku[web.1]: State changed from starting to up
2012-01-31T23:27:32+00:00 heroku[router]: GET empty-fire-6534.herokuapp.com/ dyno=web.1 queue=0 wait=0ms service=27ms status=200 bytes=17
Looks good. We can now visit the app with heroku open.