ConfigLoggingBundle

Tue Apr 29 2025

The ConfigLoggingBundle logs the Dropwizard configuration using SLF4J. It serializes the in-memory configuration object to json and logs that json, not the contents of the original configuration file. The output contains default values set by constructors, that were not specified in the original configuration file.

To turn it on, add ConfigLoggingBundle to the list of registered bundles.

@Override
public void initialize(Bootstrap<HelloWorldConfiguration> bootstrap) {
    bootstrap.setConfigurationFactoryFactory(new JsonConfigurationFactoryFactory<>());
    bootstrap.addBundle(new EnvironmentConfigBundle());

    bootstrap.addBundle(new ObjectMapperBundle());
    bootstrap.addBundle(new ConfigLoggingBundle());

read more...

Now HelloWorldApplication will log something like this on startup:

INFO  12:53:29 [main]  {liftwizard.priority=-8, liftwizard.bundle=ConfigLoggingBundle} io.liftwizard.dropwizard.bundle.config.logging.ConfigLoggingBundle: Inferred Dropwizard configuration:

Output configuration

{
  "template": "Hello, %s!",
  "defaultName": "Stranger",
  "configLogging": {
    "enabled": true
  },
  // ...
  "metrics": {
    "frequency": "1 minute",
    "reporters": [ ]
  }
}

Original configuration

{
  "configLogging": {
    "enabled": true
  },
  "template": "Hello, %s!"
}

Note that the metrics section at the end was not specified in test-example.json5. It comes from serializing the output of io.dropwizard.Configuration.getMetricsFactory().

io.dropwizard.Configuration

@JsonProperty("metrics")
public MetricsFactory getMetricsFactory() {
    return metrics;
}

This output can be helpful for fleshing out the configuration file with default options. Including "redundant" defaults makes it easier to edit the configuration by hand. It's easier to flip a boolean flag from false to true than to first figure out where in the configuration file it belongs and the exact spelling of its key.

The ConfigLoggingBundle also logs the "default" configuration at the DEBUG level. It does this by instantiating a new copy of the configuration class using the default no-arg constructor, serializing it to json, and logging it. The default configuration output can be useful for finding redundant configuration to remove.

Adding the dependency

ConfigLoggingBundle lives in the liftwizard-bundle-logging-config module.

<dependency>
    <groupId>io.liftwizard</groupId>
    <artifactId>liftwizard-bundle-logging-config</artifactId>
</dependency>