Creating and running Hello World with sbt

§Creating and running Hello World with sbt

A Lagom system is typically made up of a set of sbt builds, with each build containing multiple services. The easiest way to get started with sbt is to create a new build using the sbt Giter8 lagom template.

The lagom-java template uses the .sbtopts file to increase the memory used by the JVM when starting your project. See Increase Memory in sbt for other ways to configure memory usage.

Follow these steps to create your first Lagom build:

  1. Create a new Lagom build
  2. Browse the build
  3. Run Hello World

§Create a new Lagom build

Choose a location on your file system for your Lagom projects. The template will prompt you for a project name and will create a directory with that name that contains the build structure and Lagom example services. Note that it can take from a few seconds to a few minutes for sbt to download dependencies.

To create your project, follow these steps:

  1. Open a console and change into the directory you selected for your project.

  2. Enter the following command to invoke sbt new using the Lagom Giter8 template:
    sbt -Dsbt.version=0.13.16 new https://github.com/lagom/lagom-java.g8

  3. The sbt Lagom template prompts for the following parameters. Press Enter to accept the defaults or specify your own values:
  • name - Becomes the name of the top-level directory.
  • organization - Used as a package name.
  • version - A version number for your system.
  • lagom-version - The version number of Lagom, such as 1.3.2. Be sure to use the current stable release.

§Browse the build

The build created by the template contains the following elements:

hello                   → Project root
 └ hello-api            → hello api project
 └ hello-impl           → hello implementation project
 └ hello-stream-api     → hello-stream api project
 └ hello-stream-impl    → hello-stream implementation project
 └ project              → sbt configuration files
   └ build.properties   → Marker for sbt project
   └ plugins.sbt        → sbt plugins including the declaration for Lagom itself
 └ build.sbt            → Build configuration
  • Notice how each service is broken up into two projects: api and implementation. The api project contains a service interface through which consumers may interact with the service, while the impl project contains the actual service implementation.
  • The project folder contains sbt specific files.
  • The build.sbt file contains all information necessary to build, run, and deploy your services.

§Run Hello World

Lagom includes a development environment that let you start all your services by simply typing runAll in the sbt console. From a console change directories to the top-level directory and start sbt, when the command prompt displays, invoke runAll:

cd hello
sbt
... (booting up)
> runAll

It will take a bit of time to build the project and start the services. Among other messages, you should see the following:

[info] Starting embedded Cassandra server
..........
[info] Cassandra server running at 127.0.0.1:4000
[info] Service locator is running at http://localhost:9008
[info] Service gateway is running at http://localhost:9000
[info] Service helloworld-impl listening for HTTP on 0:0:0:0:0:0:0:0:24266
[info] Service hellostream-impl listening for HTTP on 0:0:0:0:0:0:0:0:26230
(Services started, press enter to stop and go back to the console...)

You can verify that the services are indeed up and running by invoking a service endpoint from any HTTP client, such as a browser:

http://localhost:9000/api/hello/World

The service returns the message, Hello, World!. Congratulations! You’ve created and run your first Lagom system.

Found an error in this documentation? The source code for this page can be found here. Please feel free to edit and contribute a pull request.