Package org.apache.juneau.config

Class ConfigPropertySourceProvider

java.lang.Object
org.apache.juneau.config.ConfigPropertySourceProvider
All Implemented Interfaces:
PropertySourceProvider
public class ConfigPropertySourceProvider extends Object implements PropertySourceProvider
Auto-registers a classpath-default juneau.cfg (and the other names returned by Config.getCandidateSystemDefaultConfigNames()) as a PropertySource for the process-wide Settings singleton.

Discovered by ServiceLoader-based wiring through a META-INF/services/org.apache.juneau.commons.settings.PropertySourceProvider entry shipped in this module.

Lookup semantics: the registered source defers calling Config.getSystemDefault() to the first get(name) invocation. This is deliberate — calling getSystemDefault() from inside create() would create a static-initialization cycle because Settings.<clinit> fires the ServiceLoader at class-load time, and Config's static initializers transitively reference Settings (through Cache / SystemUtils.env(...)) which would re-enter the Settings.<clinit> block.

Lazy resolution makes the cycle a non-issue: by the time @Value("${...}") fires its first lookup, all participating classes are fully initialized.

Silence on missing config:

If no system-default Config is discoverable (no juneau.cfg / default.cfg / application.cfg / etc. on the classpath or working directory), get(name) returns PropertyLookupResult.missing() for every key. No logging, no exception — many deployments have no classpath config and shouldn't see noise.

Ordering:

order() returns 100, which is "low" in the PropertySourceProvider scheme — provider-discovered classpath defaults register near the bottom of the source list so that programmatic Settings.get().addSource(...) calls (e.g. per-microservice config or the Spring Environment bridge) shadow the classpath default. Settings walks sources in reverse insertion order, so the most-recently-added source wins.