The simplest Dropwizard service

The simplest Dropwizard service you can have.

It does absolutely nothing except start when using config.yml, which defines a minimal logging configuration.

However, if you try to start with either config-empty.yml or config-only-yaml-marker.yml the service will not start. The reason is that they do not define any configuration at all.

Using config.yml

$ mvn -q package
$ java -jar target/simplest-dropwizard-service-0.1.0-SNAPSHOT.jar server config.yml
...
...lots of initialization, elided here for brevity...
...
INFO  [2023-12-17 20:54:16,630] org.eclipse.jetty.server.AbstractConnector: Started application@30d25c03{HTTP/1.1, (http/1.1)}{0.0.0.0:8080}
INFO  [2023-12-17 20:54:16,631] org.eclipse.jetty.server.AbstractConnector: Started admin@7a1f8def{HTTP/1.1, (http/1.1)}{0.0.0.0:8081}
INFO  [2023-12-17 20:54:16,631] org.eclipse.jetty.server.Server: Started Server@756b58a7{STARTING}[11.0.18,sto=30000] @642ms

Using config-empty.yml

$ mvn -q package
$ java -jar target/simplest-dropwizard-service-0.1.0-SNAPSHOT.jar server config-empty.yml
io.dropwizard.configuration.ConfigurationParsingException: config-empty.yml has an error:
  * Configuration at config-empty.yml must not be empty

	at io.dropwizard.configuration.ConfigurationParsingException$Builder.build(ConfigurationParsingException.java:278)
	at io.dropwizard.configuration.BaseConfigurationFactory.build(BaseConfigurationFactory.java:91)
	at io.dropwizard.core.cli.ConfiguredCommand.parseConfiguration(ConfiguredCommand.java:139)
	at io.dropwizard.core.cli.ConfiguredCommand.run(ConfiguredCommand.java:85)
	at io.dropwizard.core.cli.Cli.run(Cli.java:78)
	at io.dropwizard.core.Application.run(Application.java:94)
	at com.acme.simple.App.main(App.java:14)

Using config-only-yaml-marker.yml

$ mvn -q package
$ java -jar target/simplest-dropwizard-service-0.1.0-SNAPSHOT.jar server config-only-yaml-marker.yml
java.lang.IllegalArgumentException: HV000116: The object to be validated must not be null.
	at org.hibernate.validator.internal.util.Contracts.assertNotNull(Contracts.java:44)
	at org.hibernate.validator.internal.engine.ValidatorImpl.validate(ValidatorImpl.java:151)
	at io.dropwizard.configuration.BaseConfigurationFactory.validate(BaseConfigurationFactory.java:270)
	at io.dropwizard.configuration.BaseConfigurationFactory.build(BaseConfigurationFactory.java:149)
	at io.dropwizard.configuration.BaseConfigurationFactory.build(BaseConfigurationFactory.java:94)
	at io.dropwizard.core.cli.ConfiguredCommand.parseConfiguration(ConfiguredCommand.java:139)
	at io.dropwizard.core.cli.ConfiguredCommand.run(ConfiguredCommand.java:85)
	at io.dropwizard.core.cli.Cli.run(Cli.java:78)
	at io.dropwizard.core.Application.run(Application.java:94)
	at com.acme.simple.App.main(App.java:14)

Making it work

You can make it work using either config-empty.yml or config-only-yaml-marker.yml by uncommenting the greeting in those files.

Then, the service will start up and log a greeting that starts with the value from the configuration file.