Overriding config values with command line arguments

Often you may wish to override a configuration value with a value provided on the command line. One way to do this is to add a SystemPropertiesConfigSource as the last source in Gestalt. This way it will have the highest priority and override all previous sources.

Then when running the project you provide the command line parameter -D<path.to.config=value>. This will override all other config sources with this value.

In this example we provide a config source for default and dev, but allow for the overriding those with the system properties.

with the property values

# default
http.pool.maxTotal=100
# dev
http.pool.maxTotal=1000

However, we override with a command line parameter of: -Dhttp.pool.maxTotal=200

  // for this to work you need to set the following command line Options
  // -Dhttp.pool.maxTotal=200
  GestaltBuilder builder = new GestaltBuilder();
  Gestalt gestalt = builder
      .addSource(ClassPathConfigSourceBuilder.builder().setResource("default.properties").build())
      .addSource(ClassPathConfigSourceBuilder.builder().setResource("dev.properties").build())
      .addSource(SystemPropertiesConfigSourceBuilder.builder().build())
      .build();

  // Load the configurations, this will throw exceptions if there are any errors.
  gestalt.loadConfigs();

  GestaltConfigTest.HttpPool pool = gestalt.getConfig("http.pool", GestaltConfigTest.HttpPool.class);
  
  Assertions.assertEquals(200, pool.maxTotal);

In the end we should get the value 200 based on the overridden command line parameter.