Creating and running Hello World with Maven

§Creating and running Hello World with Maven

The easiest way to get started with Lagom and Maven is to use the Maven archetype plugin and a Lagom archetype to create a new project. A Maven project includes sub-projects organized in sub-directories. The top-level and sub-project directories each include a Project Object Model (POM) that contains build configuration. When you run the generate command, Maven prompts you for POM element values. The Lagom archetype creates a project that includes two Lagom services, hello and stream.

Follow these instructions to create and run your first project:

  1. Generate a project with the Lagom archetype
  2. Browse the project structure
  3. Run Hello World

§Generate a project with the Lagom archetype

Choose a location on your file system for your Lagom projects. Maven 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 Maven 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. Invoke mvn archetype:generate from the command line:

    mvn archetype:generate -Dfilter=com.lightbend.lagom:maven-archetype-lagom-java
    

    Maven starts in interactive mode and prompts you to choose an archetype:

    Choose archetype:
    1: remote -> com.lightbend.lagom:maven-archetype-lagom-java (maven-archetype-lagom-java)
    Choose a number or apply filter (format: [groupId:]artifactId, case sensitive contains): :
    
  3. Enter the number that corresponds with com.lightbend.lagom:maven-archetype-lagom-java (at time of writing, the number 1, and the only one available).
    Maven prompts you for the version.

  4. Enter the number corresponding with the version of Lagom you want to use. We recommend using the current stable release).
    The template prompts you for POM values.
  5. Specify values for:
    • groupId - Usually a reversed domain name, such as com.example.hello.
    • artifactId - Maven also uses this value as the name for the top-level project folder. You might want to use a value such as my-first-system
    • version - Press Enter to accept the default or enter a version number for your project.
    • package - Press Enter to accept the default, which is the same as the groupId.
      Maven prompts you to confirm POM values.
  6. Enter Y to accept the values.
    When finished, Maven creates the project, and completes with a message similar to the following:
   [INFO] ------------------------------------------------------------------------
   [INFO] BUILD SUCCESS
   [INFO] ------------------------------------------------------------------------
   [INFO] Total time: 10:42 min
   [INFO] Finished at: 2017-02-24T11:58:08-06:00
   [INFO] Final Memory: 17M/252M
   [INFO] ------------------------------------------------------------------------

§Browse the project structure

The structure for a project created with the Maven archetype generate command will look similar to the following (assuming my-first-system as an artifactId):

my-first-system
 └ hello-api/             → hello world api project dir
 └ hello-impl/            → hello world implementation dir
 └ integration-tests/
 └ stream-api/            → stream api project dir
 └ stream-impl/           → stream implementation project dir
 └ pom.xml                → Project group build file

Note that the hello and stream services each have:

  • An api project that contains a service interface through which consumers can interact with the service.
  • An impl project that contains the service implementation.

§Run Hello World

Lagom provides a runAll command to start the Lagom hello and stream services and runtime components, which include: Cassandra, Akka, and Kafka. From the top-level group directory, such as my-first-system, execute lagom:runAll.

For example:

cd my-first-system
mvn lagom:runAll

It will take a bit of time for the services to start. The Services started message indicates the system is running:

...
[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 127.0.0.1:65499
[INFO] Service hello-impl listening for HTTPS on 127.0.0.1:50695
[INFO] Service stream-impl listening for HTTP on 127.0.0.1:60212
[INFO] Service stream-impl listening for HTTPS on 127.0.0.1:58440
[INFO] (Services started, press enter to stop and go back to the console...)

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

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

The request 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.