§Creating and running Hello World with sbt
A Lagom system is typically made up of a set of sbt builds, with each build providing multiple services. The easiest way to get started with a new Lagom system is to create a new project using the
lagom sbt Giter8 template. This creates an sbt project, with two services,
stream. The 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 increase memory.
Follow these steps to create and run Hello World:
§Create the 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:
Open a console and change into the directory you selected for your project.
Enter the following command:
sbt new lagom/lagom-scala.g8
- The template prompts for the following parameters. Press
Enterto accept the defaults or specify your own values:
name- Becomes the name of the top-level project 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 created project 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 → Your project build file
- Notice how each service is broken up into two projects: api and implementation. The
apiproject contains a service interface through which consumers may interact with the service. The
implproject contains the actual service implementation.
projectfolder contains sbt-specific files.
build.sbtfile 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. To run Hello World, change directories to the top-level directory and start sbt, when the command prompt displays, invoke
runAll. For example:
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 hello-impl listening for HTTP on 0:0:0:0:0:0:0:0:24266 [info] Service hello-stream-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...)
Verify that the services are indeed up and running by invoking one of its endpoints from any HTTP client, such as a browser:
The service returns the message,
Hello, World!. Congratulations, you’ve built your first Lagom project!