Launcher

The launcher is an alternative to using CoreContext directly for deployments. The Launcher can be combined with dynamically deployed services.

It adds the following functionality

• a CommandExecutor that parses the commandline and executes an operation.
• deployment of service blocks, ie a block of services configured for a specific host.

See: com.codingchili.core.Launcher and com.codingchili.core.context.

Deployment configuration

A deployment block contains a set of deployable services. When the com.codingchili.core.Launcher is set as the main class these blocks can be deployed by passing the block name for the launcher option --deploy <blockName>. Using hosts mapping we can specify the block using the hostname of the deploying machine, no block name should then be specified for the deploy command.

Example launcher configuration in YAML.

version: CORE-1.0.5-PR
application: prototype
clustered: false
warnOnDefaultsLoaded: true
blocks:
  default:
  - com.codingchili.logging.Service
  - com.codingchili.authentication.Service
  - com.codingchili.realm.Service
  - com.codingchili.router.Service
  - com.codingchili.social.controller.SocialHandler
  - com.codingchili.website.Service
  - com.codingchili.realmregistry.Service
  router:
  - com.codingchili.router.Service
  website:
  - com.codingchili.website.Service
  social:
  - com.codingchili.social.Service
  logger:
  - com.codingchili.logging.Service
  realm:
  - com.codingchili.realm.Service
  authentication:
  - com.codingchili.authentication.Service
hosts:
  laptop4: website

Breakdown

Name	description
version	The running version of the application, used for logging etc.
application	The name of the running application, used for logging etc.
clustered	Indicates if a Hazelcast cluster should be joined.
warnOnDefaultsLoaded	Warns whenever configuration is missing on disk and defaults are loaded from the java class.
blocks	a list of name:services pair to be deployed when passing the –deploy option.
hosts	a list of hosts which has a specific default block to deploy.

Example using the com.codingchili.core.Launcher with another main-class.

public static void main(String[] args) {
    Launcher.main(args);
}

Another example with programmatic configuration

public static void main(String[] args) {
    LaunchContext context = new LaunchContext(args);
    
    context.settings()
        .setApplication("sample app")
        .setVersion("1.0.0")
        .setClustered(true);
    
    Launcher.start(context);    
}

Commandline parser

The commandline parser can be used to implement command-line functionality.

This is an example that adds a single command to the default command executor. When invoked with the --print-cat option the program writes cat a few times to the console as specified by the -upper option. To write multiple cats, specify the -times option.

The command returns SHUTDOWN to indicate that the application should shut down after the command has completed.

    public static void main(String[] args) {
        LaunchContext context = new LaunchContext(args)
        CommandExecutor executor = new DefaultCommandExecutor();
        
        executor.add((future, executor) -> {
            Integer times = Integer.parseInt(executor.getProperty("times").orElse("1"));
        
            for (int i = 0; i < times; i++) {
                System.out.println(executor.hasProperty("-upper") ? "CAT" : "cat");
            }
            
            executor.complete(CommandResult.SHUTDOWN);
        }, "--print-cat", "prints the word cat n times.");
        
        Launcher.start(context);
    }

The command receives a future object to facilitate asynchronous calls as well as a reference to the current context.

A sample invocation would look like

java -jar <file.jar> --print-cat -upper -times 100

The order of the parameters

Useful interfaces

Name	Description
CommandExecutor	Parses the commandline and executes a matching command.
Command	Implementation of an executable command.
CommandResult	Indicates if the Launcher should continue with deployment or shut down.

The types that can be returned from a Command

CONTINUE	After the command is invoked the Launcher should continue with deployment.
STARTED	THe command has handled the deployment and the launcher will not.
SHUTDOWN	The application will be terminated by the Launcher.

Note that it is possible to use the CommandExecutor implementations without the use of a Launcher. In this case it is up to the caller to interpret the result of the command execution.